Phylogenetic revision of Gymnotidae (Teleostei: Gymnotiformes), with descriptions of six subgenera

The diversity of gymnotid electric fishes has been intensely studied over the past 25 years, with 35 species named since 1994, compared to 11 species in the previous 236 years. Substantial effort has also been applied in recent years to documenting gymnotid interrelationships, with seven systematic studies published using morphological and molecular datasets. Nevertheless, until now, all gymnotids have been assigned to one of just two supraspecific taxa, the subfamily Electrophorinae with one genus Electrophorus and three valid species and the subfamily Gymnotine also with one genus Gymnotus and 43 valid species. This simple classification has obscured the substantial phenotypic and lineage diversity within the subfamily Gymnotine and hampered ecological and evolutionary studies of gymnotid biology. Here we present the most well-resolved and taxon-complete phylogeny of the Gymnotidae to date, including materials from all but one of the valid species. This phylogeny was constructed using a five-gene molecular dataset and a 115-character morphological dataset, enabling the inclusion of several species for which molecular data are still lacking. This phylogeny was time-calibrated using biogeographical priors in the absence of a fossil record. The tree topology is similar to those of previous studies, recovering all the major clades previously recognized with informal names. We propose a new gymnotid classification including two subfamilies (Electrophorinae and Gymnotinae) and six subgenera within the genus Gymnotus. Each subgenus exhibits a distinctive biogeographic distribution, within which most species have allopatric distributions and the subgenera are diverged from one another by an estimated 5–35 million years. We further provide robust taxonomic diagnoses, descriptions and identification keys to all gymnotid subgenera and all but four species. This new taxonomy more equitably partitions species diversity among supra-specific taxa, employing the previously vacant subgenus and subfamily ranks. This new taxonomy renders known gymnotid diversity more accessible to study by highlighting the deep divergences (chronological, geographical, genetic and morphological) among its several clades.


Introduction
The family Gymnotidae Rafinesque is represented by 46 valid species and seven valid subspecies [1], with at least two additional species currently known and being described elsewhere (Table 1). Despite its relative species richness, the family Gymnotidae is currently divided into only two supraspecific (higher) taxa, one of which is the subfamily Electrophorinae with a single genus (Electrophorus) and three valid species and the other the subfamily Gymnotinae also with a single genus (Gymnotus) and 43 valid species. The geographic distributions of Gymnotus species span two continents, from the Rio Motagua in Guatemala (G. cylindricus LaMonte, at 15˚N) to the Rio Salado in Argentina (G. carapo australis Craig et al.,at 35˚S) [2] (Table 2). Gymnotus species exhibit a variety of phenotypes, ranging from meter-long floodplain piscivores (e.g. G. inaequilabiatus) to small-bodied forms of 15 cm (e.g. G. coropinae) that inhabit in small forest streams and consume small benthic animals [3][4][5].
Knowledge of Gymnotus species diversity has expanded rapidly in the past 20 years [5][6][7] (Fig 1), with the descriptions of 34 species or 77% of the currently-known diversity of this clade. This expansion of knowledge at the species level has been accompanied by seven major efforts to create a systematic classification of the genus. Seven publications [5,[8][9][10][11][12][13] each introduced species-group taxonomies within Gymnotus, which although lacking some species and occasionally incongruent in their inter-group relationships, are notable for their broad similarities (Tables 3 and 4). Thus, concurrent with a rapid increase in our understanding of Gymnotus as a species-rich genus, an informal but widely-accepted taxonomy was developed for use below the genus level.
In this study we present the most well resolved and taxon-complete phylogeny of Gymnotus to date, including all valid species as of this writing and synthesizing a wealth of morphological data (115 characters, including aspects of color pattern, morphometrics and osteology) with a five-gene mitochondrial and nuclear dataset (16S, COX1, CYT-B, RAG2 & ZIC1, approximately 3,000 bp). These data were analyzed using the model-based total evidence (MBTE) framework described in [12], resulting in a well-resolved phylogeny, which was then time-calibrate using biogeographic priors in the absence of pertinent fossils. We propose a new classification of the family Gymnotidae that includes two subfamilies (Electrophorinae and Gymnotinae, following [14]), two genera (Electrophorus, Gymnotus) and six subgenera within the genus Gymnotus. This new classification more completely reflects the current understanding of gymnotid diversity and phylogeny, with subgenera that correspond to previously-recognized and readily recognizable species-groups. This new classification highlights the relatively deep phylogenetic divergences among the gymnotid clades recognized as subgenera and makes gymnotid diversity more accessible to the broader ichthyological community.

Taxon sampling
The gymnotiform species Hypopomus artedi and Sternopygus macrurus were used as outgroups in all phylogenetic analyses. Morphological data, including aspects of coloration, morphology, meristics and osteology, were collected for 790 specimens including all 43 valid described Gymnotus as of this writing, as well as two undescribed species herein designated G. n. sp. 'ARAP' and G. n. sp. 'ARIP', following methods in [9] and [1]. Type specimens were included in the analysis whenever possible; the authors personally examined type material for 93% of the Gymnotidae (excluding only G. interruptus, G. capitimaculatus and G. pantherinus). Written consent for all project activities was approved by UL Lafayette IACUC #2010-8717-064 for all activities related to this specific project and the resulting manuscript. All authors of this manuscript, where applicable, have given written informed consent (as outlined in PLOS consent form) to publish their image as well as any specific case details. Each participant's copy of The Consent Form for Publication in a PLOS Journal has been securely filed in the individual's case notes.

Retrieving orthologous DNA sequences from GenBank
The package phyLotaR [15] was used for identifying and retrieving orthologous sequence clusters of Gymnotus (NCBI:txid36670) from GenBank release 230 (February 15 2019, available here: https://www.ncbi.nlm.nih.gov/genbank/release/230/). This package is an implementation of the PhyLota Browser [16], a pipeline that implements BLAST searches [17] to both identify and download sequence clusters for listed taxonomic groups to assemble a robust collection of sequences in a reproducible way based on publicly-available gene sequences while avoiding selection bias on the part of the assembler. Importantly, PhyLota always recovers the same groups of sequences given the same starting taxon and the same GenBank release (old releases are available online). We then reviewed all sequence clusters identified for Gymnotus (S1 Supplementary Material) and chose those that had at least 25% of the taxon sampling of Gymnotus diversity (i.e. > 14 sequences) total 13 independent markers. The sequences assembled by phyLotaR as discussed above were then combined with the gymnotid sequences compiled by [12] and available in the supplemental material for that study. and Albert and [8], pages 668-670 and are not reproduced here for brevity. The resulting morphological matrix used in all analyses and a table defining the character codings, is presented in S3 Supplementary Material.

Nucleotide substitution model selection
For the molecular dataset, optimal partitioning schemes and nucleotide substitution models were estimated in PartitionFinder 2 [45]. Two independent analyses were conducted to estimate the best partitioning schemes including substitution models implemented in Garli 2.01 [46] and MrBayes 3.2 [47]. Each analysis assumed a fully partitioned dataset (by gene and by codon position in protein-coding genes) and the best-fit partitioning scheme with its respective substitution models was selected according to the Akaike Information Criterion with correction (AICc). Substitution models with a proportion of invariant sites (+I) were excluded because the rate of heterogeneity is already accounted by the gamma shape parameters (+C).
For the morphological dataset, the Mkv model was applied for discrete character evolution. In the Mkv model, M refers to Markov chain, k refers to the number of discrete character states (with k>2) and v refers to the number of variable characters [48]. The Mkv model used here is discussed in detail in [12,48]; in summary, it applies simple parsimony in a likelihood framework, creating independent partitions for molecular and morphological data which can be treated using different evolutionary models.

Maximum-likelihood phylogenetic inference
Maximum-likelihood (ML) analyses of combined morphological + molecular (hereafter supermatrix) datasets were conducted in Garli 2.01 [46]. Models of nucleotide evolution were estimated in PartitionFinder 2 [45]. The Mkv model [48] was used for the morphological dataset. The ML analyses consisted of two independent runs, each one starting from a BioNJ starting tree and using the Subtree Pruning and Regrafting (SPR) algorithm to search for tree improvement in terms of likelihood scores. All other parameters were set as default. To assess node support, 100 non-parametric bootstrap replications were performed for each independent tree search resulting in a total of 200 pseudo-replicates. A consensus tree with bootstraps was computed using the function SumTrees from DendroPy 3.7.0 [49].

Bayesian phylogenetic inference
The Bayesian inference (BI) analysis of supermatrix datasets was conducted in MrBayes 3.2 [47]. Models of nucleotide evolution were estimated in PartitionFinder 2 [45]. Mkv model [48] was used for the morphological dataset, as discussed above. The BI analysis consisted of two runs (four chains each) of the Metropolis-Coupled Markov Chain Monte Carlo (MC 3 ). Each run was comprised of 5.0 x 10 7 generations with generation. All other parameters were set as default. To ensure model parameter values and a single tree sampled every 5 x 10 3 adequate mixing of the MCMC, effective sample size values (ESS > 200) were inspected for parameter estimates in Tracer 1.5. The two independent runs were summarized with ''sump" and ''sumt" commands in MrBayes 3.2 [47]. The initial 25% of sampled topologies were discarded as burnin procedure. The remaining topologies were used to construct a 50% majority-rule consensus tree. Posterior probabilities were visualized in FigTree 1.4.0.3 [50].
with color pattern, dentition and the number of preopercular-mandibular sensory canal pores in the dorsoposterior portion of the preopercle all shared by all species of the G. cylindricus clade. In all phylogenetic analyses where robust molecular data are included for the G. cylindricus clade, we recover their location as sister to the G. carapo clade. Notably, the G. cylindricus clade is also similar to the G. carapo clade on many osteological characters (see the full diagnoses of each presented below) further suggesting a deep homology between the two and that the morphology-only analyses fell victim to over-parameterization of the characters associated with color pattern.
Second, the morphology-only parsimony and Bayesian phylogenies recover a monophyletic group comprising the species G. pantanal, G. riberalta and G. capanema as sister to the G. anguillaris clade. We interpret this result to arise from a shared suite of characters associated with a long, cylindrical body, including a longer body cavity with more precaudal vertebrae and a slender body profile. This topology is unique to the morphology-only trees, whereas in all molecular and total-evidence analyses, the G. carapo clade is recovered as monophyletic, including the species G. pantanal, G. riberalta and G. capanema. We propose that the morphology-only analyses fail to recover a monophyletic G. carapo clade, which is well supported by a wealth of genetic data as well as aspects of color pattern, dentition and osteology. Notably in this particular case, G. pantanal, G. riberalta and G. capanema occasionally possess a single preopercular-mandibular sensory canal pore at the dorsoposterior corner of the preopercle, a condition also observed in species of the G. anguillaris clade, but which appears to be a phylogenetic reversal to the ancestral, single-pored state present other Gymnotus. These two aspects of the morphological analyses, which stand out as incongruent with the molecular and total-evidence analyses, serve to emphasize the importance of character selection and of the power of the total-evidence approach to overcome potentially misleading aspects of the morphological dataset.

Characterization of major clades
In both the Bayesian (Fig 2) and Maximum-Likelihood (Fig 3) phylogenies we recover more than 20 clades within Gymnotinae, including six main clades within Gymnotus, all with distinct morphological characteristics, geographic distributions and relatively deep phylogenetic divergences from one another. These clades correspond broadly to those recovered in previous taxonomic and phylogenetic treatments of the family [5,[8][9][10][11][12][13].
We recover the "G. carapo clade" sensu [12], which is equivalent to the subgenus Gymnotus diagnosed herein. The subgenus Gymnotus is a continentally-distributed clade with 22 valid species ranging from the Pacific slope of Colombia to northern Argentina, making it the most species-rich, phenotypically disparate and geographically widespread subgenus within the family.
We recover the "G. cylindricus clade" sensu [12], which is equivalent to the subgenus Tijax designated herein. Tijax includes three of the four gymnotid species in Central America, where all three species are endemic [5,8,57].
We recover the "G. tigre clade" sensu [12], which is equivalent to the subgenus Tigre designated herein. Tigre is the second most geographically widespread subgenus of the Gymnotinae, with its five species distributed from 8˚N in southern Panama to 34˚S in northern Argentina. Tigre also includes G. henni from Pacific draining rivers of Colombia and southern Panama.
We recover the "G. coatesi clade" sensu [12], which is equivalent to the subgenus Tigrinus designated herein. The seven species of Tigrinus are distributed through the Amazon-Orinoco-Guianas core of the Neotropics and are absent from drainages in the Trans-Andean and La Plata regions.
We recover the "G. anguillaris clade" sensu [12], which is equivalent to the subgenus Lamontianus designated herein. The six species of Lamontianus (including two new species currently in review) are distributed throughout the Eastern Amazon and rivers draining the Guiana and Brazilian Shields.
We recover the "G. pantherinus clade" sensu [12], which is equivalent to the subgenus Pantherus designated herein. The three species of Pantherus species are limited to coastal drainages of eastern and southeastern Brazil [30,58] and the Tietê river of the Paraná (La Plata) basin.

Relationships among subgenera
Our total evidence approach recovers the subgenus Pantherus as the sister to all other gymnotine subgenera. This result is consistent with the total-evidence and molecular-only results of [12], who applied a similar approach but used substantially fewer taxa and morphological characters. This result was not recovered in the multigene molecular phylogeny of [10], however that phylogeny did not reach a fully-resolved topology with respect to their G. pantherinus clade, recovering the group in a three-member polytomy consisting of the subgenus Pantherus (their G. pantherinus clade), Lamontianus (their "G2 clade") and the subgenera Gymnotus and Tijax (represented only by G. cylindricus).
We recover the subgenus Tigrinus as the sister to the other four remaining subgenera. This result is consistent with those of [10] and [12].
We recover the subgenus Lamontianus as the sister to the other three remaining subgenera. This result is consistent with that of [12] but not [10], who recover Lamontianus within a polytomy as discussed above.
We recover the subgenus Tigre as the sister to the other two remaining subgenera. This is consistent with the molecular and total-evidence phylogenies presented by [12], but not recovered in their morphological analysis, which finds Tigre nested within Gymnotus. Similarly, [10] recovered G. tigre, the only subgenus Tigre species in their analyses, nested within subgenus Gymnotus as well. We propose that an improved osteological dataset and higher taxon sampling contributed the increased phylogenetic resolution for this clade.
We recover the subgenera Gymnotus and Tijax as sister clades. This result is consistent with the total-evidence analyses of [12], but not their morphology-only analysis, which found the subgenus Tijax as the sister group to the other clades. The phylogeny of [9], which included G. carapo, G. anguillaris and G. cylindricus, also found G. cylindricus as sister clade to the other two, but relatively poor taxon sampling likely influenced this result. This present study follows a similar methodology to that of [12], but draws upon a larger sampling of species within Gymnotinae. The total-evidence dataset presented in [12] includes 67% of the subgenus Gymnotus, 67% of the subgenus Tijax, 40% of the subgenus Tigre, 71% of the subgenus Tigrinus, 75% of the subgenus Lamontianus (not including undescribed species reported here) and 33% of the subgenus Pantherus, whereas the present study includes all but one valid species of Gymnotidae. The topology recovered here is broadly similar to that of [12], with the major exception being the monophyly of a clade comprised of the subgenera Lamontianus and Tigrinus. This relationship had previously been hypothesized by [22] based on morphology exclusively, but never previously recovered in genetic or total evidence studies.

Historical biogeography
Our total-evidence phylogeny, relying on biogeographical markers for time-calibration, recovers the age of the crown-group Gymnotidae between 61 and 50 Ma, with the clade Gymnotinae arising between 50 and 35 Ma,Pantherus between 36 and 2.5 Ma,Lamontianus between 21 and 11 Ma,Tigrinus between 21 and 12 Ma,Tigre between 21 and 11 Ma, Tijax between 14 and 6.0 Ma and Gymnotus between 17 and 10 Ma.
Historical biogeographic analysis suggests the clade composed of Gymnotus, Tigre and Tijax originated in the Western Amazon about 20 Ma and subsequently colonized trans-Andean, Central American and Southern (La Plata) drainages on multiple separate occasions. Pantherus is unique among gymnotines in being estimated to have originated on the Southeastern Atlantic coast, with one dispersal to the upper Tietê (upper Parana) presumably by river capture [59]. Tigrinus is estimated to have originated in the Amazon-Orinoco-Guianas region. Lamontianus is estimated to have arisen on the Amazon Craton prior to the origin of the modern trans-continental Amazon river c. 10 Ma [60,61]. The Amazon Craton consists of the Guianas shield and the northern portion of the Brazilian shield, largely corresponding to the "Eastern Highlands" of Eigenmann [62].
We recover a polyphyletic assemblage of trans-Andean and Central American gymnotines, composed of seven species representing three distinct clades, each representing a different subgenus. First, crown group Tigre appeared between 25 and 15 Ma. Gymnotus esmeraldas and G. henni, both found only in trans-Andean drainages, arose about 10.0 +/-3.0 Ma (this date, however, was used for the time calibration and is therefore not a result of this analysis). Second, crown-group Tijax appeared between 25 and 2.5 Ma, suggesting that Tijax dispersed to Central America during the Miocene or Pliocene, perhaps in the Early to Middle Miocene, before rise of the Panamanian isthmus [63]. Third, the trans-Andean species of Gymnotus, (i.e. G. ardilai and G. choco), are most closely related to one another and together most closely related to the cis-Andean species G. carapo septentrionalis from the Orinoco basin [64].
We also recover a polyphyletic fauna of the eastern and southeastern basins of Brazil and the La Plata basin. This fauna is composed of 11 species representing seven distinct clades in three subgenera: Pantherus with three species in one clade, Tigre with two species in one clade and Gymnotus with seven species in five clades. These clades of Gymnotus include: 1) G. pantanal that arose between 3.5 and 3.0 Ma and is most closely related to G. riberalta from the upper Madeira basin; 2), G. bahianus and G. interruptus that arose 1.5 to 0.5 Ma and are most closely related to G. carapo occidentalis from the Western Amazon; 3) a clade including a population of G. carapo australis, G. chimarrao, G. diamantinensis, G. omarorum and G. sylvius from the upper Parana that arose 12.0 to 2.0 Ma that is most closely related to a clade composed of G. mamiraua from the central Amazon and G. eyra from the upper Madeira basin; 4) a clade comprised of another population of G. (G.) carapo australis plus G. cuia that arose 1.5 to 0.5 Ma and is most closely related to the clade listed above (comprising some G. carapo australis, G. chimarrao, G. diamantinensis, G. omarorum and G. cf. sylvius from the upper Paraná basin; 5) a comprised of yet other population of G. carapo australis, G. cf. carapo from the Sao Francisco basin and G. sylvius from Ribeiro de Iguapé basin that arose 1.0 to 0.1 Ma and is most closely related to G. carapo occidentalis from the Western Amazon. Taken together, these data suggest the southern humid Neotropics was colonized by the Gymnotinae on at least five  (45 Gymnotinae,one Electrophorinae, two outgroup) species. Colors of clades as follows: red = Gymnotus, orange = Tijax, Yellow = Tigre, green = Tigrinus, blue = Lamontianus, purple = Pantherus, grey = Electrophorus, black = outgroups. Node colors indicate bootstrap support values of nodes, from 100% (green) to 0% (red).
https://doi.org /10.1371/journal.pone.0224599.g003 Revision of Gymnotidae with descriptions of six subgenera different occasions between 5.5 and 0.1 Ma, with four of these clades originating in the Western Amazon and dispersing through the upper Madeira and Paraguay-Paraná basins of the Sub-Andean foreland basin [65].

Utility of newly designated subgenera
In this study we constructed the most taxon-complete and character-rich morphological dataset to date for the family Gymnotidae and paired it with a robust multigene dataset (Fig 4). The results of this study improve our phylogenetic understanding of the group, incorporating for the first time all but one of the currently valid species. We recover six major clades of the Gymnotinae, largely similar with results of previously published studies (Fig 5).
The newly proposed classification formalizes an already well-established informal taxonomy of the group [13]. The benefits of applying the subgenus rank to these clades case are threefold. Dividing the 43 valid species of Gymnotidae into six subgenera increases the utility of these named groups for researchers less knowledgeable in the fields of gymnotiform systematics or Neotropical Ichthyology. While introducing new names does create more complexity it also highlights phenotypically and ecologically distinct taxa. For example, it would benefit an ecologist to know that Gymnotus (Tigre) species are typically large-bodied (up to 500 mm) floodplain predators, whereas Gymnotus (Tigrinus) species rarely exceed one eighth that size and mostly inhabit small upland rainforest streams [4,28,66,67]. Similarly, a biogeographer may be interested to know that Gymnotus (Tijax) is an exclusively Central American taxon, while Gymnotus (Pantherus) is largely endemic to the southeastern coastal drainages of Brazil. In all these cases, the added work of learning new names rewards researchers with a wealth of information that is phylogenetically structured, information that would otherwise remain buried in "variation" within a single genus. Finally, we offer these new subgeneric names as a more effective taxonomy to summarize the evolutionary relationships of the subfamily. Each of the subgenera in the new classification possesses a distinct suite of morphological and ecological phenotypes and each exhibits a distinctive biogeographical range. Sublimating all the diversity exhibited by these clades within a one undifferentiated genus has made these differences almost invisible to all but the most dedicated researchers. With these ideas in mind, we propose the first major revision to the Linnaean genus Gymnotus in its 260-year history.

Historical biogeography
Our time-calibrated phylogeny reveals a history of multiple colonizations of major biogeographic regions, resulting in the well-documented pattern of polyphyly of local species assemblages [62,68]. The Central American and trans-Andean drainages were colonized at least twice each and the Southern Neotropics was colonized by at least five gymnotine clades in our analysis. In the latter case, these dispersal events appear to have originated in the Western Amazon and proceeded through the upper Madeira basin along the Sub-Andean foreland as described by [69]. While our data support a Western Amazon origin for several clades, Gymnotus (Lamontianus) appears to have originated in Eigenmann's "Eastern Highlands" region on the Amazon Craton, prior to the origin of the modern trans-continental Amazon river c. 10 Ma.

Summary
This study reviews the known diversity and phylogenetic interrelationships of electric fishes of the family Gymnotidae (Gymnotiformes), a species-rich clade distributed throughout most of the humid Neotropics. The family is currently known from 46 species, representing an increase of >400% from the 11 species listed in the seminal review of gymnotiform fishes by  [34]. Species of the subfamily Gymnotinae are members of one genus Gymnotus, itself divided into six subgenera. Each subgenus is a clade with a readily recognized and distinctive phenotype, a unique biogeographic distribution, multiple species that have largely or entirely allopatric distributions and are diverged from one other by 10-30 million years. These six clades have been previously recognized with informal names and are here described as subgenera within the subfamily Gymnotinae. The taxonomy proposed more equitably partitions species diversity among supraspecific taxa, employs the previously vacant subgenus taxonomic rank and renders the known diversity of the family Gymnotidae more accessible to comparative study.
Description. Sexually dimorphic, with males larger at maturity. Adult size >2 m TL in males, >1 m TL in females. Adult body shape subcylindrical with a mean ratio of body width to depth of 80.8% HL. Body profile slender, body depth .5% head length. Preanal distance long, 72.5-100% head length. Anal-fin long, 70.5-81.8% total length. Scales absent over entire body.
Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla triangular with a curved ventral margin, length equal to >10 dentary teeth. Dentary with one row of >16 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process absent. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch absent, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin concave, posterior margin with ridges or spines.
Cleithrum very narrow with straight ventral margin, anterior limb short, less than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity extremely long; 145-200 precaudal vertebrae in examined specimens, with this number increasing through the lifespan of the fish. Rib 5 robust along its entire extent, less than three times width of rib 6. Pectoral fin extremely broad, with 30 rays. Anal fin long, with >400 rays in adult specimens. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body.

Gymnotinae ellis
Diagnosis. Readily distinguishable from Electrophorinae by the following characters: adult body size <1 m, lacking male-biased sexual size dimorphism in all species except G. (Tigrinus) coatesi and G. (Tigrinus) javari (vs. females >1 TL, males >2m in Electrophorinae), no addition of new vertebrae (vs. continuous addition throughout lifetime in Electrophorinae), cycloid scales over entire body (vs. scales absent in Electrophorinae), one hypaxial electric organ (vs. three anatomically-separate hypaxial electric organs in Electrophorinae), hemal spines present and body cavity short (vs. hemal spines absent with body cavity extending to tip of tail in Electrophorinae), anal-fin rays ending before tip of tail (vs. extending to tip of tail in Electrophorinae), anal fin with 390 or fewer rays (vs. >400 in Electrophorinae), narrow parasphenoid enveloping orbitosphenoid and Pterosphenoid (vs. broad in Electrophorinae).
Description. Sexually monomorphic (Except G. (T.) javari). Size up to 998 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 59.7%. Body profile slender, body depth 55.7-133.3% total length. Head length variable, 7.2-15.0% total length. Snout length moderate, .2% head length. Anal-fin long, 62.0-92.3% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line variable, in 4-13 rows. Scales over anal-fin pterygiophores variable, with 4-16 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with 5-15 teeth disposed in two rows along outer margin, median margin straight or curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a shorter than to almost-as-long-as ventral margin, length equal to 4-9 dentary teeth. Dentary with one row of 5-16 teeth, 0-10+ arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large or small, depth greater or less than posterior process. Dentary anteroventral margin with or without a hook. Anguloarticular process absent to large, extending to or beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight or curved, tip simple or complex. Interopercle dorsal margin ascending process present or absent. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves separate or combined. Preopercle anteroventral notch present or absent, posterodorsal laterosensory ramus with 1-2 superficial pores, margin of medial shelf smooth, median shelf small to large, less to greater than half width of symplectic. Opercle dorsal margin convex to concave, posterior margin smooth.
Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight or rounded, postorbital process narrow to broad, less to greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust or reduced, extends beyond or to lateral process. Parasphenoid posterior processes gracile or robust. Prootic foramen Vp combined with or separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar. Cleithrum narrow with straight ventral margin, anterior limb long to short, greater to less than 1.8 times ascending limb, with or without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity variable, with 31-58 precaudal vertebrae. Rib 5 robust to broad along its entire extent, less to greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin variable, with 9-22 rays. Anal fin long, with 130-390 rays. Lateral-line complete, with 2-55 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3-10 rows of electroplates near caudal insertion of anal fin.
Gymnotus (Gymnotus) subgen nov. (Table 5).   Diagnosis. Species of the subgenus Gymnotus are readily distinguishable from those of other subgenera of Gymnotinae by the following characters: anteriormost 2-7 dentary teeth anteroposteriorly compressed, resembling arrowheads (vs. conical or needle-shaped teeth in other subgenera), transparent patch in posterior 10-20% of anal fin membrane (vs. evenly pigmented or striped in other subgenera). Gymnotus (Gymnotus) is morphologically most similar to Gymnotus (Tijax), from which is it readily distinguishable by the following characters, a color pattern consisting of 14-29 dark, unevenly spaced, obliquely-oriented, dark pigment bands or band-pairs with wavy, low-contrast margins (except in G. (G.) diamantinensis and G. (G.) bahianus that lack pigment bands) vs. a color pattern lacking dark pigment bands, or with small, irregular dark pigment blotches (except in G. (Tijax) panamensis, which possesses dark pigment bands only on the posterior 33% of the body); 2, one row of premaxillary teeth vs. two. Gymnotus (Gymnotus) is readily distinguishable from morphologically similar Gymnotus (Tigre) by the following characters, color pattern lacking white blotches on head vs. color pattern with white blotches on head, ovoid-shaped scales over the whole body surface (vs. axiallyelongate scales posteriorly), relatively few, long, curved ventral latera-line rami  vs. many, short, straight ventral lateral-line rami , body cavity of intermediate length   Scales above lateral line of intermediate size, in 4-10 rows. Scales over anal-fin pterygiophores large, arranged in 4-13 rows. Gape large, extending to or posterior to posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid (or tear-drop shaped in lateral view in G. (G.) carapo occidentalis and G. (G.) arapaima). Premaxilla with 8-14 teeth disposed in one row along outer margin, medial margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally (except in G. (G.)  Endopterygoid superior and inferior portions approximately equal in size, endopterygoid ascending process robust, long, its base shorter than length (except in G. (G.) cuia and G. (G.) omarorum), endopterygoid ascending process straight or slightly curved, with a simple tip (except in G. (G.) eyra and G. mamiraua where it is divided into several smaller processes). Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected (except in G. (G.) capanema, G. (G.) pantanal and G. (G.) riberalta). Preopercle anteroventral notch present (except in G. (G.) curupira), posterodorsal laterosensory ramus with two superficial pores, margin of medial shelf entirely smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight or convex, posterior margin entirely smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal broad or narrow, anterior margin straight, postorbital process broad or narrow. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterosphenoid anteroventral portion robust, extending ventrally to lateral margin of parasphenoid (except in G. (G.)  Diagnoses and descriptions of each species of subgenus Gymnotus ( Tables 6-12) Gymnotus ( (Gymnotus) arapaima can be differentiated from all other members of the subgenus except G. (G.) carapo, G. (G.) sylvius and G. (G.) ucamara on the basis of the following characters: long head   diamantinensis, 8.9-12.3% in G. (G.) eyra, 9.6-11.9% in G. (G.) mamiraua, 9.9-11.3% in G. (G.) obscurus, 10.6-12.4% in G. (G.) omarorum, 7.2-11.7% in G. (G.) pantanal, 7.3-10.3% in G. (G.) riberalta, 9.1-10.3% in G. (G.) varzea). Gymnotus (Gymnotus)   fin long, 76.6-81.5% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage. Scales above lateral line intermediate, in 5-10 rows. Scales over anal-fin pterygiophores large, with 9-13 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation position near tip of endopterygoid. Maxilla rod-or paddleshaped, broad distally with a curved ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, >8 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin without a hook. Mandible long.

Diagnosis. Gymnotus
Anguloarticular process long, extending over ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, long, base>length, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight or convex, posterior margin entirely smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process large, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends ventrally to lateral process. Parasphenoid posterior processes gracile, elongate. Prootic foramen Vp separate V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar. Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, small facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 34-37 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 15-17 rays. Anal fin long, with 220-275 rays. Lateral-line complete, with 14-18 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3-4 rows of electroplates near caudal insertion of anal fin.
Diagnosis. Gymnotus (Gymnotus) ardilai can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern with dark band pairs present over entire body in juveniles and subadults (TL <250 mm), but absent anteriorly in large adults (TL >350 mm) (vs. always banded or spotted in all other Gymnotus).
Description Scales above lateral line intermediate, in [8][9] rows. Scales over anal-fin pterygiophores large, with 9-10 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla vertical, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin without a hook. Mandible long. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple.
Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf entirely smooth, median shelf large, greater than half width of symplectic. Opercle dorsal
Description. Sexually monomorphic. Size up to 273 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 64.1%. Body profile slender, body depth 82.9-113.7% total length. Head length short, 10.3-12.6% total length. Snout length moderate, 33.5-36.4% head length. Mouth Scales over anal-fin pterygiophores large, with 7-8 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of 12-15 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Mandible short. Anguloarticular process long, extending over ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, long, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends ventral to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp divided V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb short, less than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 32-35 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin intermediate, with 16-16 rays Diagnosis. Gymnotus (Gymnotus) capanema can be differentiated from all other members of the subgenus except G. (G.) pantanal and G. (G.) riberalta on the basis of the following characters: color pattern with wide (>5X width of interbands) dark bands, where pale interbands restricted to the ventral part of the lateral surface such that the dark interbands fuse into a uniform dark coloration over anterior 60% of body (vs. banded or spotted in all other Gymnotus). Gymnotus (Gymnotus) capanema can be differentiated from G. (G.) pantanal and G. (G.) riberalta on the basis of the following characters: pectoral fin possessing an intermediate number of rays (P1R 12-15 in G. (G.) capanema vs. 14-18 in G. (G.) pantanal, 10-13 in G. (G.)

riberalta).
Description. Sexually monomorphic. Size up to 166 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 63.0%. Head length short, 8.5-9.3% total length. Snout length moderate, 36.4-39.8% head length. Mouth width narrow, 40.6-58.0% head length. Preanal distance long, 77.6-125%head length. Anal-fin long, 80.6-82.7% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 6-8 rows. Scales over anal-fin pterygiophores large, with 5-8 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla vertical, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of 12 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf broad, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes short, stout. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity intermediate, with 36-37 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin small, with 12-15 rays. Anal fin long, with 180-205 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3-4 rows of electroplates near caudal insertion of anal fin.
Scales above lateral line intermediate, in 5-8 rows. Scales over anal-fin pterygiophores large, with 6-12 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla vertical, rod-or paddle-shaped distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending over ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends ventral to lateral process. Parasphenoid posterior processes gracile. Prootic foramen Vp separate from V2-3 +VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum board with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 32-43 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin variable, with 13-17 rays. Anal fin long, with 173-290 rays. Lateral-line complete, with 18-21 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3-4 rows of electroplates near caudal insertion of anal fin.

Description
Sexually monomorphic. Size up to 275 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 77.6%. Body profile slender, body depth 69.6-109.7% total length. Head length short, 8.8-13.6% total length. Snout length moderate, 32.3-39.8% head length. Mouth width narrow, 35.5-52.8% head length. Preanal distance long, 61.3-99.4%head length. Anal-fin long, 80.2-86.2% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 5-9 rows. Scales over anal-fin pterygiophores large, with 12-13 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla vertical, rod-or paddle-shaped distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of <12 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth longer than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Description
Sexually monomorphic. Size up to 243 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 39.2%. Body profile slender, body depth 68.3-99.7% total length. Head length short, 9.7-11.3% total length. Snout length moderate, 31.7-41.6% head length. Mouth width narrow, 33.8-46.9% head length. Preanal distance long, 68.5-87.1%head length. Anal-fin long, 76.6-83.8% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 6-8 rows. Scales over anal-fin pterygiophores large, with 9-13 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of 12-15 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin absent a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple. Interopercle dorsal margin ascending process absent. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to ventral lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 14-17 rays. Anal fin long, with 191-250 rays. Lateral-line complete, with 13-24 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.  Gymnotus (Gymnotus) choco can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern with intermediate (2-5X width of interbands) dark bands, irregular, wavy band margins, pale interbands restricted to the ventral part of the lateral surface anteriorly and 1-3 dark bands divided ventrally to form inverted-"Y" shapes (vs. spotted, with dark bands <2X or >5X width of pale interbands in all other Gymnotus).

Description
Sexually monomorphic. Size up to 260 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 76.9%. Body profile slender, body depth 68.9-93.3% total length. Head length short, 11.1-13.3% total length. Snout length moderate, 31.9-35.9% head length. Mouth width narrow, 31.3-37.2% head length. Preanal distance long, 76.7-90.7%head length. Anal-fin long, 75.8-83.8% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 6 rows. Scales over anal-fin pterygiophores large, with 8-9 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes gracile. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Description
Sexually monomorphic. Size up to 305 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 46.8%. Body profile slender, body depth 94.5-130.5% total length. Head length short, 9.8-12.2% total length. Snout length moderate, 29.9-38.3% head length. Mouth width narrow, 37.5-52.7% head length. Preanal distance long, 51.2-95.7%head length. Anal-fin long, 76.3-92.3% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 5-7 rows. Scales over anal-fin pterygiophores large, with 6-10 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-shaped, narrow distally with a curved ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin narrow, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Diagnosis
Gymnotus (Gymnotus) curupira can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern with majority of dark bands divided ventrally to form inverted-"Y" shapes (vs. no bands forming inverted-"Y" shapes in all other Gymnotus except G. (G.) choco, with 1-3 inverted-"Y" shapes). Scales over anal-fin pterygiophores large, with 7-8 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of 12-15 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch absent, posterodorsal laterosensory ramus with one superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Description
Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 34-36 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 16-17 rays. Anal fin long, with 230-322 rays. Lateral-line complete. Lateralline dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin. Scales over anal-fin pterygiophores large, with 9 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curbed. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes narrow. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Description
Sexually monomorphic. Size up to 254 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 55.4%. Body profile slender, body depth 85.4-114.5% total length. Head length short, 8.9-12.3% total length. Snout length moderate, 32.0-39.9% head length. Mouth width narrow, 30.9-43.9% head length. Preanal distance long, 61.3-84.5%head length. Anal-fin long, 78.5-84.9% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 4-6 rows. Scales over anal-fin pterygiophores large, with 6-8 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a curved ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of 12-15 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip complex. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin convex, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with straight ventral margin, anterior limb short, less than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity intermediate, with 32-34 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin narrow, with 10-13 rays. Anal fin long, with 155-227 rays. Lateral-line complete, with 10-15 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.

Description
Sexually monomorphic. Size up to 121 mm TL with adult body proportions attained at about 150 mm TL. Head length long, 12.8-14.3% total length. Anal-fin long, 80.8-82.0% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 9 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth.
Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of 12-15 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Diagnosis
Gymnotus (Gymnotus)   Scales over anal-fin pterygiophores large, with 6-8 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of 12-15 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip complex. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb short, less than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity intermediate, with 32-34 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin narrow, with 11-13 rays. Anal fin long, with 155-227 rays. Lateral-line complete, with 10-15 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.  Gymnotus (Gymnotus)  Scales above lateral line intermediate, in 4-7 rows. Scales over anal-fin pterygiophores large, with 6-7 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a curved ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of 12-15 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf long, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Diagnosis
Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 35-37 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 20-22 rays. Anal fin long, with 208-250 rays. Lateral-line complete. Lateralline dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3-4 rows of electroplates near caudal insertion of anal fin.  Scales above lateral line intermediate, in 5-7 rows. Scales over anal-fin pterygiophores large, with 5-6 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Diagnosis
Gymnotus (  Scales over anal-fin pterygiophores large, with 7-8 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-shaped, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of <12 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 1-2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar. Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 37-38 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 14-18 rays. Anal fin long, with 131-280 rays. Lateral-line complete, with 13-19 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.  Gymnotus (Gymnotus) riberalta can be differentiated from all other members of the subgenus except G. (G.) capanema and G. (G.) pantanal on the basis of the following characters: color pattern with wide (>5X width of interbands) dark bands, where pale interbands restricted to the ventral part of the lateral surface such that the dark interbands fuse into a uniform dark coloration over anterior 60% of body (vs. banded or spotted in all other Gymnotus). Gymnotus (Gymnotus)

Description
Sexually monomorphic. Size up to 302 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 65.0%. Body profile slender, body depth 81.1-102.1% total length. Head length short, 7.3-10.3% total length. Snout length moderate, 31.0-37.3% head length. Mouth width narrow, 32.7-45.7% head length. Preanal distance long, 71.9-97.9%head length. Anal-fin long, 79.7-97.4% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 6-8 rows. Scales over anal-fin pterygiophores large, with 6-8 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of <12 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 36 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin narrow, with 10-13 rays. Anal fin long, with 169-240 rays. Lateral-line complete, with 10-16 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.

Description
Sexually monomorphic. Size up to 291 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 47.5%. Body profile slender, body depth 33.6-70.2% total length. Head length long, 10.7-14.1% total length. Snout length moderate, 30.2-36.1% head length. Mouth width narrow, 30.2-42.7% head length. Preanal distance long, 60.3-68.1%head length. Anal-fin long, 76.0-85.7% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 7 rows. Scales over anal-fin pterygiophores large, with 6-9 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple. Interopercle dorsal margin ascending process absent. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Description
Sexually monomorphic. Size up to 188 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 66.0%. Body profile slender, body depth 78.0-90.0% total length. Head length intermediate, 11.7-12.7% total length. Snout length moderate, 34.1-38.6% head length. Mouth width narrow, 37.0-46.4% head length. Preanal distance long, 60.0-70.5%head length. Anal-fin long, 81.4-82.4% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 7 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rodor paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, 4-7 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process.
Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity short, with 33 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin intermediate, with 15 rays. Anal fin long, with 215 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.  Gymnotus (Gymnotus)  Scales above lateral line intermediate, in 5-9 rows. Scales over anal-fin pterygiophores large, with 4-6 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of <12 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Diagnosis
Cleithrum broad with curved ventral margin, anterior limb broad, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity variable, with 35-40 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 16-19 rays. Anal fin long, with 230-310 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3-4 rows of electroplates near caudal insertion of anal fin.

Description
Sexually monomorphic. Size up to 337 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 62.3%. Body profile slender, body depth 59.0-106.8% total length. Head length moderate, 9.7-31.9% total length. Snout length moderate, 26.2-39.7% head length. Mouth width narrow,  length. Anal-fin long, 65.9-85.0% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 5-13 rows. Scales over anal-fin pterygiophores large, with 5-10 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with 11 or more teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of needle-shaped teeth. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook present in lateral view. Mandible long and extended. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, long, straight (except in G. (L.) tiquie), tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf smooth (except in G. (L.) pedanopterus), median shelf large, greater than half width of symplectic (except in G. (L.) pedanopterus). Opercle dorsal margin straight or convex, posterior margin entirely smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal broad, anterior margin straight (except in G. (L.) tiquie), postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterosphenoid anteroventral portion reduced, extends dorsally to lateral margin of parasphenoid. Parasphenoid posterior processes robust, with shallow, convex posterior margin. Prootic foramen Vp combined with V2-3+VII. M. adductor mandibula intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, lacking large facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 31-58 precaudal vertebrae. Rib 5 with broad medial triangular shelf, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin intermediate, with 9-18 rays. Anal fin of moderate length, with 210-312 rays. Lateral-line reduced, with 2-18 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.

Etymology
Subgenus name to honor Francesca Raymond LaMonte , Assistant Curator of Ichthyology at the American Museum of Natural History, for contributions to gymnotiform taxonomy and ichthyology as a whole. Among her 86 articles and several books [73], LaMonte (1935) described two gymnotid species, Gymnotus (Tijax) cylindricus and Gymnotus (Tigrinus) coatesi, each representing the types species of their respective subgenus.
Diagnoses and descriptions of each species of Lamontianus (Table 13) Scales over anal-fin pterygiophores large, with 9 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of >16 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin Revision of Gymnotidae with descriptions of six subgenera squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar. Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 37-38 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 15-18 rays. Anal fin long, with 210-270 rays. Lateral-line complete, with 16 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body.  Gymnotus (Lamontianus) cataniapo can be differentiated from all other members of the subgenus on the basis of the following combination of characters: color pattern with many dark band pairs  anguillaris, 18-27 in G. (L.) pedanopterus, 19-24 in G. (L.) tiquie), especially long body cavity  anguillaris, 31-32 in G. (L.)

Description
Sexually monomorphic. Size up to 316 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 73.4%. Body profile slender, body depth 71.4-106.8% total length. Head length short, 8.8-11.1% total length. Snout length moderate, 36.2-37.4% head length. Mouth width narrow, 38.0-44.4% head length. Preanal distance long, 102.5-188.2%head length. Anal-fin long, 81.5-84.7% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 8-10 rows. Scales over anal-fin pterygiophores large, with 6 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-shaped, narrow distally, length equal to 7-9 dentary teeth. Dentary with one row of >16 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process absent. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp connected to V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Description
Sexually monomorphic. Size up to 337 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 64.0%. Body profile slender, body depth 38.7-56.1% total length. Head length variable, 8.0-14.2% total length. Snout length moderate, 31.0-26.0% head length. Mouth width narrow, 31.5-37.3% head length. Preanal distance long, 50.7-143.9% head length. Anal-fin long, 75.1-85.0% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 7-13 rows. Scales over anal-fin pterygiophores large, with 8 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of >16 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf serrate, median shelf small, less than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity intermediate, with 31-32 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin narrow, with 12-14 rays. Anal fin long, with 222-312 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body.

Description
Sexually monomorphic. Size up to 240 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 53.1%. Body profile slender, body depth 85.9-95.8% total length. Head length short, 8.7-9.5% total length. Snout length moderate, 35.4-39.7% head length. Mouth width narrow, 48.5-58.3% head length. Preanal distance long, 90.8-108.3% head length. Anal-fin long, 81.0-82.0% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage. Scales above lateral line intermediate, in 7-8 rows. Scales over anal-fin pterygiophores large, with 8-9 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, broad distally, length equal to >10 dentary teeth. Dentary with one row of >16 teeth, >5 needle-shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process long, curved, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin rounded, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 45 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 15-17 rays. Anal fin long, with 210-265 rays. Lateral-line complete. Lateralline dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body.

Other included species
G. (P.) capitimaculatus, G. (P.) refugio. Gymnotus (Pantherus) is readily distinguishable from all other subgenera of the Gymnotinae by the following characters: a color pattern consisting of irregular dark color blotches about 3-4 scales in diameter, with blurry, low-contrast margins covering entire body vs. band pairs in all other subgenera except Gymnotus (Tijax), which possesses small, irregular dark pigment spots 2-3 scales in diameter.

Description
Sexually monomorphic. Size up to 234 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 47.6%. Body profile slender, body depth 69.9-99.6% total length. Head length moderate, 8.6-13.1% total length. Snout length moderate, 24.4-37.6% head length. Mouth width narrow, 31.5-51.2% head length. Preanal distance long, 80.7-123.5% head length. Anal-fin long, 64.8-81.7% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage. Scales above lateral line intermediate, in 5-9 rows. Scales over analfin pterygiophores large, with 4-11 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with more than 11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rodor paddle-shaped, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of 12-15 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin hook present in lateral view. Mandible long and extended. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, long, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf entirely smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight or convex, posterior margin entirely smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal broad, anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterosphenoid anteroventral portion reduced, extends dorsally to lateral margin of parasphenoid. Parasphenoid posterior processes robust with a shallow posterior margin. Prootic foramen Vp combined with V2-3+VII. M. adductor mandibula intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, lacking large facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity log, with 48 precaudal vertebrae. Rib 5 with broad medial triangular shelf, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin large, with 14-19 rays. Anal fin of intermediate length, with 173-232 rays. Lateralline complete, with 5-29 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.
Diagnoses and descriptions of each species of Pantherus (Table 14)

Diagnosis
Gymnotus (Pantherus) capitimaculatus can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern with irregular dark color blotches with blurry, low contrast margins and a pair of white blotches on ventral portion of the head, anterior to or directly below eye (vs. irregular dark color blotches with blurry, low contrast margins with evenly pigmented head, lacking any blotches).

Description
Sexually monomorphic. Size up to 158 mm TL with adult body proportions attained at about 150 mm TL. Head length short, 8.8-9.9% total length. Snout length moderate, 17.7-20.7% head length. Anal-fin long, 75.2-78.5% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage. Scales above lateral line intermediate, in 9 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla paddle-shaped, broad distally with a straight ventral margin, length equal to >10 dentary teeth. Dentary with one row of 12-15 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified.
Gill rakers not contacting gill bar. Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 45 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent.

Description
Sexually monomorphic. Size up to 189 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 48.5%. Body profile slender, body depth 68.5-87.7% total length. Head length short, 7.9-11.1% total length. Snout length moderate, 27.9-35.3% head length. Mouth width narrow, 30.1-48.6% head length. Preanal distance long, 72.4-126.7% head length. Anal-fin long, 63.6-78.5% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage. Scales above lateral line intermediate, in 6-9 rows. Scales over anal-fin pterygiophores large, with 6-11 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid.
Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to >10 dentary teeth. Dentary with one row of 12-15 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 15-17 rays. Anal fin long, with 158-237 rays. Lateral-line complete, with 14-31 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.  Scales over anal-fin pterygiophores large, with 4-9 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla paddle-shaped, broad distally with a straight ventral margin, length equal to >10 dentary teeth. Dentary with one row of 12-15 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Materials examined in morphological analyses
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 48 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin variable, with 14-19 rays. Anal fin long, with 173-232 rays. Lateral-line complete, with 5-29 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.

Diagnosis
Tigre is readily distinguishable from all other subgenera of the Gymnotinae by the following characters: large adult size (except G. (T.) paraguensis) with G. (T.) inaequilabiatus to 998 mm TL and G. (T.) tigre to 533 mm TL representing the two largest species in the subfamily (vs. G. (G.) carapo to 419 mm TL representing the third largest species), color pattern including large white blotches up to 3 times eye diameter (except in G. (T.) inaequilabiatus) covering the head (vs. absent in all other subgenera), dark pigment stripes at caudal end of anal-fin membrane (vs. clear patch or evenly pigmented in all other subgenera), more than 16 dentary teeth, all conical, some decurved with tips oriented outward in large specimens (vs. all straight and conical or needle-shapedneedle-shaped in the subgenera Lamontianus, Pantherus, Tigrinus and Tijax, or anteriormost 2-9 arrowhead-shaped in the subgenus Gymnotus), four to six rows of electrocytes caudally (vs. two to four rows in other subgenera), axially-elongate scales covering posterior 20% of body and caudal appendage (vs. ovoid scales over entire body in other subgenera). Gymnotus (Tigre) is morphologically most similar to Gymnotus (Gymnotus), from which is it readily distinguishable by the following characters: many, short, straight ventral lateral-line rami (VLR  vs. relatively few, long, curved ventral lateral-line rami , long body cavity  vs. body cavity of intermediate length .

Description
Sexually monomorphic. Size up to 998 mm TL in G. (T.) 45.6-112.3%head length. Anal-fin long, 73.0-87.8% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line small, in 6-13 rows. Scales over anal-fin pterygiophores small, with 9-16 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with fewer than ten teeth disposed in two rows along outer margin, median margin straight. Maxilla-palatine articulation near tip of endopterygoid. Maxilla vertical, rod-or paddle-shaped distally, length equal to width of 7-9 dentary teeth. Dentary with one row of comical teeth, occasionally decurved (points facing outward from body) in large adult specimens, all others conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process (except in G. (T.) paraguensis). Dentary anteroventral margin lacking a hook. Mandible long and extended. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, long, straight (except in G. (T.) inaequilabiatus and G. (T.) tigre), tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with two superficial pores, margin of medial shelf entirely smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin concave, posterior margin entirely smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal broad, anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterosphenoid anteroventral portion robust, extends ventrally to lateral margin of parasphenoid. Parasphenoid posterior processes robust, with shallow, convex posterior margin. Prootic foramen Vp separate from V2-3+VII. M. adductor mandibula intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, lacking large facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 32-48 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin large to very large, with 13-21 rays. Anal fin long, with 190-390 rays. Lateral-line complete, with 23-55 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3-6 rows of electroplates near caudal insertion of anal fin.

Etymology
Subgenus name derived from the local aquarium trade name of the type species, referring to the color pattern of alternating dark and light bands.
Diagnoses and descriptions of each species of Tigre (Table 15)  [8][9]. rows Scales over anal-fin pterygiophores large, with 11-13 rows. Gape large, extending to or beyond posterior nares. Mouth position Table 15. Summary of morphometric and meristic data for five species of Tigre. Data for 46 specimens. superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin straight. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of 12-15 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf long, greater than half width of symplectic. Opercle dorsal margin concave, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar. Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 41-46 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 17-19 rays. Anal fin long, with 226-260 rays. Lateral-line complete. Lateralline dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 4-5 rows of electroplates near caudal insertion of anal fin.  Gymnotus (Tigre) henni can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern with few dark band pairs  inaequilabiatus, 23-26 in G. (T.) paraguensis, 17-23 in G. (T.) tigre). Gymnotus (Tigre) henni is most morphologically similar to G. (T.) tigre, from which it differs on the basis of a relatively wide mouth  tigre), relatively short head  tigre).

Description
Sexually monomorphic. Size up to 312 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 79.9%. Body profile slender, body depth 77.0-86.9% total length. Head length intermediate, .5% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 10-13 rows. Scales over anal-fin pterygiophores large, with 10-13 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin straight. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, with a straight ventral margin. Dentary with one row of 12-15 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process absent. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Parasphenoid posterior processes robust. Prootic foramen Vp separate V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity intermediate, with 43-44 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 17-19 rays. Anal fin long, with 223-275 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3-6 rows of electroplates near caudal insertion of anal fin.

Description
Sexually monomorphic. Size up to 998 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 70.8%. Body profile slender, body depth 81.1-100.5% total length. Head length variable, .6% head length. Anal-fin long, 73.2-87.8% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 6-13 rows. Scales over anal-fin pterygiophores large, with 9-14 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin straight. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped with a straight ventral margin. Dentary with one row of 12-15 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes broad. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity intermediate, with 45 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin variable, with 13-21 rays. Anal fin long, with 214-390 rays. Lateral-line complete, with 23-38 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 4 rows of electroplates near caudal insertion of anal fin.

Materials examined in morphological analyses
straight median margin (vs. curved in all other Tigre), dentary ventral margin lamella large (>posterior process vs. <posterior process in all other Tigre).

Description.
Sexually monomorphic. Size up to 240 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 69.4%. Body profile slender, body depth 84.3-96.2% total length. Head length short, .0% head length. Anal-fin long, 79.7-81.7% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 7-12 rows. Scales over anal-fin pterygiophores large, with 14-14 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin. Dentary with one row of 12-15 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella short, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, long, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle dorsal margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity short, with 32-35 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 17-21 rays. Anal fin long, with 210-260 rays. Lateral-line complete, with 49-55 ventral rami. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 4-4 rows of electroplates near caudal insertion of anal fin.  Gymnotus (Tigre) tigre can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern with large (5 or more scales across) irregular pale blotches on ventral and posterior portions of head and over opercle (vs. head evenly-pigmented in all other Tigre). Gymnotus (Tigre) tigre is most morphologically similar to G. (T.) henni, from which it differs on the basis of a relatively narrow mouth

Description
Sexually monomorphic. Size up to 411 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 75.6%. Body profile slender, body depth 72.8-100.6% total length. Head length long, 11.0-13.3% total length. Snout length moderate, .8% head length. Preanal distance long, 69.7-81.9% head length. Anal-fin long, 73.0-80.1% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 11-12 rows. Scales over anal-fin pterygiophores large, with 13-16 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin straight. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin. Dentary with one row of 12-15 teeth, 2-4 arrowhead shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, curved, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves divided. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 2 superficial pores, margin of medial shelf smooth, median shelf large, greater than half width of symplectic. Opercle posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp separate from V2-3 +VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 41-48 precaudal vertebrae. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 17-19 rays. Anal fin long, with 190-240 rays. Lateral-line complete. Lateralline dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3-6 rows of electroplates near caudal insertion of anal fin.
Gymnotus (Tigrinus), subgen. nov. (Table 5 Diagnosis Gymnotus (Tigrinus) is readily distinguishable from all other subgenera of the Gymnotinae by the following characters: a color pattern consisting of evenly spaced, often unpaired, straight dark pigment bands with high-contrast (sharp) margins (except G. (T.) onca with large dark blotches, equal in width to 10+ scales) vs. wavy dark pigment band pairs in the subgenera Gymnotus, Lamontianus and Tigre and dark spots or blotches in the subgenera Pantherus and Tijax, dentary with five or more narrow, needle-shaped teeth vs. all conical in the subgenera Lamontianus (except G. (L.) tiquie), Pantherus, Tigre and Tijax and some arrowhead-shaped in the subgenus Gymnotus, very narrow cleithrum with a straight ventral margin vs. narrow with a straight ventral margin in the subgenera Lamontianus and Pantherus and broad with a curved ventral margin in the subgenera Gymnotus, Tigre and Tijax, more than 18 unbranched anal-fin rays vs.10-17 in other subgenera. Gymnotus (Tigrinus) is morphologically most similar to Gymnotus (Lamontianus), from which is it distinguishable by the following characters: fewer anal-fin rays (AFR 135-245) vs. more (AFR 210-312), few, large anal-fin pterygiophore (APS) scales (5-7) vs. many small APS scales (9)(10), end of maxilla paddle shaped (broad distally) vs. rod-shaped (narrow distally). Scales above lateral line of intermediate size, in 6-9 rows. Scales over anal-fin pterygiophores large, with 5-7 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with few to more than 11 teeth (except in G. (T.)  . Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, long, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf entirely smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin straight or convex, posterior margin entirely smooth. Subopercle dorsal margin concave. Cranial fontanels closed in juveniles and adults. Frontal broad, anterior margin rounded (except in G. (T.) coatesi and G. (T.) javari), postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterosphenoid anteroventral portion robust or reduced, extends to lateral margin of parasphenoid. Parasphenoid posterior processes robust or gracile. Prootic foramen Vp combined with V2-3+VII. M. adductor mandibula intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Description
Cleithrum very narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, lacking large facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity of intermediate length, with 35-44 precaudal vertebrae. Rib 5 broad with triangular medial shelf, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin variable, with 12-20 rays. Anal fin of intermediate length, with 135-245 rays. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.

Etymology
Subgenus name derived from the Northern Tiger Cat, Leopardus tigrinus (Schreber 1775), a relatively smaller and distinctly-colored species of Felidae. Introducing this name, in combination with the subgenera Tigre and Pantherus, continues the convention of naming gymnotids for felids, which are often similarly nocturnal, predatory and banded or spotted. (Table 16)

Materials examined in morphological analyses
Diagnosis Gymnotus (Tigrinus) coatesi can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern with 15-17 unpaired dark bands, pale interbands wider dorsally on anterior 50% of body, up to 50% width of dark band pairs, or 25% in ventral portion of same band (vs.

Description
Sexually monomorphic. Size up to 180 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 82.5%. Body profile slender, body depth 56.8-71.2% total length. Head length intermediate, 10.0-11.7% total length. Snout length moderate, 30.9-37.2% head length. Mouth width narrow, 27.8-35.1% head length. Preanal distance long, 80.9-83.7% head length. Anal-fin long, 77.8-81.0% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 6-8 rows. Scales over anal-fin pterygiophores large, with 6-7 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of >16 teeth, >5 needle-shaped anteriorly, all others conical posteriorly. Posterodorsal and  Revision of Gymnotidae with descriptions of six subgenera posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity variable, with 36-43 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin intermediate, with 15 rays. Anal fin long, with 214-223 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.

Materials examined in morphological analyses
palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of >16 teeth, >5 needle-shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin rounded, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum very narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, with facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 39-43 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin narrow, with 12-14 rays. Anal fin long, with 183-245 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.

Description
Sexually dimorphic, with adult males longer than females [74]. Size up to 220 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 70.2%. Body profile slender, body depth 55.7-89.1% total length. Head length short, 7.8-11.1% total length. Snout length moderate, 30.2-36.9% head length. Mouth width narrow, 31.1-43.2% head length. Preanal distance long, 70.6-120.9% head length. Anal-fin long, 70.8-81.1% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 7-9 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, broad distally, length equal to 7-9 dentary teeth. Dentary with one row of >16 teeth, >5 needle-shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes robust. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum very narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity long, with 40-44 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin variable, with 13-20 rays. Anal fin long, with 180-240 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin. Scales over anal-fin pterygiophores large, with 5 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin straight. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of <12 teeth, >5 needle-shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella large, depth greater than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process short, extending to ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process absent. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch smooth, posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin rounded, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process reduced, extends to lateral process. Parasphenoid posterior processes gracile. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Materials examined in morphological analyses
Cleithrum narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity intermediate, with 36-39 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Anal fin long, with 135-165 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin. Gymnotus (Tigrinus) onca can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern with dark band pairs replaced by large (>10 scales across), irregular dark brown blotches over entire body (vs. dark bands or band pairs in all other Tigrinus).

Description
Sexually monomorphic. Size up to 116 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 65.2%. Body profile slender, body depth 87.3% total length. Head length short, 8.8% total length. Snout length moderate, 30.4% head length. Mouth width narrow, 41.2% head length. Preanal distance long, 63.7% head length. Anal fin long, 72.4% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 8 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin. Dentary with one row of <12 teeth. Body cavity intermediate, with 35 precaudal vertebrae. Pectoral fin narrow, with 13 rays. Anal fin long, with 180 rays. Lateral-line complete. Lateralline dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body. Scales above lateral line intermediate, in [8][9] rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with >11 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rod-or paddle-shaped, narrow distally with a straight ventral margin, length equal to 7-9 dentary teeth. Dentary with one row of >16 teeth, >5 needle-shaped anteriorly, all others conical posteriorly. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella short, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip simple. Interopercle dorsal margin ascending process present. Preopercle anteroventral notch present, posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin round, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.

Materials examined in morphological analyses
Cleithrum very narrow with straight ventral margin, anterior limb long, greater than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity intermediate, with 41-43 precaudal vertebrae. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin narrow, with 12-14 rays. Anal fin long, with 190-245 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin. Gymnotus (Tijax), subgen. nov. (Table 5 Gymnotus (Tijax) is readily distinguishable from all other subgenera of the Gymnotinae by the following characters: a color pattern lacking dark pigment bands entirely, with small, irregular dark pigment spots 2-3 scales in diameter (except in G. (T.) panamensis, which possesses dark pigment bands only on the posterior 33% of the body), a sickle-shaped maxilla with a curved dorsal margin (shared only with G. (L.) tiquie), a short ascending process of the endopterygoid (shared only with G. (G.) cuia and G. (G.) omarorum), range of all species restricted to Central America (shared only with G. (T.) henni). Tijax is morphologically most similar to Gymnotus, from which is it readily distinguishable by the following characters: two rows of premaxillary teeth vs. one, small preopercular marginal shelf, less than half of the width of the symplectic vs. greater, prootic foramenae Vp combined with V2 & VII vs. separate from V2 & VII.

Description
Sexually monomorphic. Size up to 236 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 66.4%. Body profile moderate, body depth 71.9-114.3% total length. Head length short, 9.1-11.6% total length. Snout length moderate, 34.0-41.5% head length. Mouth width narrow, 36.1-50.1% head length. Preanal distance long, 84.2-109.6% head length. Anal-fin long, 78.4-84.2% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 7-11 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla sickle-shaped, broad distally with a concave ventral margin, length equal to width of 4-6 dentary teeth. Dentary with one row of conical teeth. Posterodorsal and posteroventral dentary processes over ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin lacking a hook. Mandible short and compressed. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, short, tip complex (except in G. (T.) panamensis). Interopercle dorsal margin ascending process present (except in G. (T.) panamensis). Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch absent, posterodorsal laterosensory ramus with one superficial pore, margin of medial shelf entirely smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin straight or convex, posterior margin entirely smooth. Subopercle dorsal margin concave (except in G. (T.) panamensis). Cranial fontanels closed in juveniles and adults. Frontal broad, anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal (except in G. (T.) panamensis). Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterosphenoid anteroventral portion robust, extends ventrally to lateral margin of parasphenoid. Parasphenoid posterior processes gracile, elongate, posterior margin convex, deep. Prootic foramen Vp combined with V2-3+VII. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb short, less than 1.8 times ascending limb, lacking large facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Body cavity of intermediate length, with 32-36 precaudal vertebrae. Rib 5 robust along its entire extent, greater than three times width of rib 6 (except in G. (T.) panamensis, which has a broad medial triangular shelf). Displaced hemal spines absent. Pectoral fin large, with 15-16 rays. Anal fin of moderate length, with 170-270 rays. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.

Etymology
Subgenus name derived from the Mayan word (and astrological sign) Tijax, meaning "knife", often made of obsidian. The Mayan civilization occupied Central America, to which the Gymnotine subgenus is endemic, for almost four thousand years and made numerous cultural and technological advancements, including the only pre-Columbian writing system developed in the Americas.

Diagnosis
Gymnotus (Tijax) cylindricus can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern lacking dark pigment bands, with dark Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla sickleshaped, narrow distally with a curved ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin without a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip complex. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch absent, posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes gracile. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum board with curved ventral margin, anterior limb short, less than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Anal fin long, with 190-200 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body. UMMZ 197103 (10), 79-231 mm, Costa Rica, Santa Rosa, near Taxisco.

Diagnosis
Gymnotus (Tijax) maculosus can be differentiated from all other members of the subgenus on the basis of the following characters: color pattern lacking dark pigment bands entirely, with small, irregular dark pigment blotches over entire body (vs. dark pigment blotches absent except in some Costa Rican localities in G. (T.) cylindricus, band pairs clearly visible on the posterior 33% of the body in G. (T.) panamensis); endocoracoid proximal portion thin (vs. broad in all other Tijax); endocoracoid distal portion not ossified (vs. ossified in all other Tijax).

Description
Sexually monomorphic. Size up to 231 mm TL with adult body proportions attained at about 150 mm TL. Adult body shape subcylindrical with a mean ratio of body width to depth of 74.9%. Body profile slender, body depth 84.0-112.2% total length. Head length short, 9.1-10.6% total length. Snout length moderate, 34.2-40.7% head length. Mouth width narrow, 36.1-40.8% head length. Preanal distance long, 94.8-109.6% head length. Anal-fin long, 78.6-81.4% total length. Cycloid or ovoid scales present on entire post-cranial portion of body from nape to caudal appendage.
Scales above lateral line intermediate, in 7 rows. Gape large, extending to or beyond posterior nares. Mouth position superior, lower jaw longer than upper, rictus decurved. Chin round in lateral, dorsal profiles, fleshy and bulbous with mental electroreceptive organ overlying lower jaw. Anterior narial pore partially or entirely included within gape, in small narial fold. Anterior nares small, its diameter less than that of eye. Eye below horizontal with mouth. Circumorbital series ovoid. Premaxilla with <10 teeth disposed in two rows along outer margin, median margin curved. Maxilla-palatine articulation near tip of endopterygoid. Maxilla rodor paddle-shaped, narrow distally with a broad ventral margin, length equal to 4-6 dentary teeth. Dentary with one row of >16 teeth, all conical. Posterodorsal and posteroventral dentary processes abuts ventral. Dentary posteroventral process shorter than or almost as long as posterodorsal, narrow distally. Dentary ventral margin lamella small, depth less than posterior process. Dentary anteroventral margin with a hook. Anguloarticular process long, extending beyond ventral margin of dentary. Retroarticular with an arched lamella posteriorly forming a small canal, posterior margin squared. Endopterygoid superior and inferior portions approximately equal in size, ascending process robust, straight, tip complex. Interopercle dorsal margin ascending process present. Dorsal region of hyomandibula with four lateral foramenae, supraorbital and infraorbital nerves connected. Preopercle anteroventral notch absent, posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin convex, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process broad, greater than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes gracile. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb short, less than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Rib 5 robust along its entire extent, less than three times width of rib 6. Displaced hemal spines absent. Anal fin long, with 170-200 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body. posterodorsal laterosensory ramus with 1 superficial pore, margin of medial shelf smooth, median shelf small, less than half width of symplectic. Opercle dorsal margin straight, posterior margin smooth. Cranial fontanels closed in juveniles and adults. Frontal anterior margin straight, postorbital process narrow, less than two times width of supraorbital canal. Lateral ethmoid unossified. Parietal rectangular, length equal to width. Pterophenoid anteroventral process robust, extends to lateral process. Parasphenoid posterior processes gracile. Prootic foramen Vp combined with V2-3+VII. Adductor mandibula insertion undivided, intermusculars absent. All basibranchials unossified. Gill rakers not contacting gill bar.
Cleithrum broad with curved ventral margin, anterior limb short, less than 1.8 times ascending limb, without facet for insertion of muscle from supracleithrum. Postcleithrum thin, discoid or sickle shaped. Rib 5 broad along its entire extent, greater than three times width of rib 6. Displaced hemal spines absent. Pectoral fin broad, with 15-16 rays. Anal fin long, with 269-270 rays. Lateral-line complete. Lateral-line dorsal rami absent in adults. Single hypaxial electric organ, extending along entire ventral margin of body with 3 rows of electroplates near caudal insertion of anal fin.

Keys to all subgenera and species of Gymnotinae
Here we present a dichotomous taxonomic key to the six new subgenera of the Gymnotinae, plus a further six keys to the species of those genera. These keys are meant to facilitate identification of these fishes by observers with some background knowledge on Neotropical fishes but who are not necessarily experts on the Gymnotiformes, such as other working ichthyologists or experienced collectors and curators. Therefore, the keys focus on readily-observable aspects of color pattern, external morphology and meristics rather than osteology, which is treated in depth in the diagnoses and descriptions above. We also include geographic ranges in rare cases where readily-observable external characters are unavailable, but the species possess well-documented, circumscribed ranges.
Key to the subgenera of Gymnotinae 1A: color pattern lacking obliquely-oriented dark pigment bands or band pairs . .