Fig 1.
Five different adult morphotypes of saccopharyngiform fishes (A–E). A, Neocyema erythrosoma (NMS.Z.2010.85.1) 157 mm TL. Photo by D. Shale (MAR-ECO). B, Monognathus jesperseni (MCZ 164702) 142 mm SL. Photo by MCZ. C, Eurypharynx pelecanoides (LACM 56986–1) 511 mm TL. Photo by D. Shale (MAR-ECO), D, Saccopharynx ampullaceus (MCZ 161545) 330 mm TL. Photo by MCZ. E, Cyema atrum (MCZ 165935) 130 mm SL. Photo by MCZ. Photos A and C reprinted from http://www.deepseaimages.co.uk and under a CC BY license, with permission from David Shale, original copyright 2009. Photos B, D and E reprinted from http://www.mcz.harvard.edu/Departments/Ichthyology and under a CC BY license, with permission from the Museum of Comparative Zoology, Harvard University, original copyright.
Fig 2.
Line-illustrations of leptocephalus larvae of meso- and bathypelagic anguilliform families (A–K). A, Cyema (Cyematidae). B, “Leptocephalus holti”. C, Monognathidae (metamorphic stage). D, Unidentified saccopharyngiform. E, Saccopharynx (Saccopharyngidae). F, Eurypharynx (Eurypharyngidae). G, Serrivomer beani (Serrivomeridae). H, Nemichthys curvirostris (Nemichthyidae). I, Avocettina infans (Nemichthyidae). J, Derichthys serpentinus (Derichthyidae). K, Nessorhamphus ingolfianus (Derichthyidae). The dotted line separates the saccopharyngiform larvae from the larvae of other meso- and bathy-pelagic eel families. Illustrations A, C, D, F–K are reproduced or modified from Böhlke [1], B is modified from Smith and Miller [24], and E is modified from Castle [84] with permission under a CC BY license, from the Sears Foundation for Marine Research original copyright 1989, illustrator Mary H. Fuges, Yale University, and the American Society of Ichthyologists and Herpetologists, Lawrence, Kansas, respectively.
Table 1.
“Saccopharyngiform” materials included in the present study corresponding to materials presented in Fig 5 that all are verified with DNA sequences.
Fig 3.
Leptocephalus larvae of saccopharyngiform fishes known until the present study (A–F). A, Eurypharynx (WH404_906) 25.3 mm. B, Saccopharynx (WH342_1580) 40.0 mm. C, Cyema (WH404_82) 26.2 mm. D, “Leptocephalus holti” Type I (KH-11-6_184) 15.4 mm. E, “Leptocephalus holti” Type II (WH342_418) 38.0 mm. F, “Leptocephalus holti” Type III (MSM41_1404) 27.1 mm. Scale bars 5 mm.
Fig 4.
A Leptocephalus larva (WH342_1248, 22.5 mm) of Neocyema erythrosoma from the Sargasso Sea that has unique orange pigment spots (A–D). A, Whole specimen, 22.5 mm TL. B, Head region. C, Esophagus, liver, stomach region. D, End of the gut region. Scale bar 5 mm.
Fig 5.
NeighborNet network (uncorrected P-distances) of larvae and adult saccopharyngiforms based on 12S rRNA MiFish DNA sequences.
The letters A–M show specimens with DNA sequences of the 12S rRNA MiFish DNA sequences used to construct the network that are matched with photos at the bottom of the figure. General illustrations are shown for adult specimens with no photos (Table 1). Scale bars 5 mm. Although we were able to associate M. jesperseni with its leptocephalus larvae (I–J), all remaining monognathid leptocephali larvae remain to be associated with adult forms.
Fig 6.
Mitogenomic phylogenetic tree of 79 taxa of the Elopomorpha based on 13 protein-coding genes in the mitochondrial genome (ML and Bayesian analyses, 11,700 base pairs).
Bootstrap replicates and Bayesian posterior probability support values for tree nodes are noted only if below 100 and 1.0, respectively. Asterisks (*) denote the only topological difference from the Bayesian analysis compared to the presented ML topology. Notacanthiform, albuliform, and elopiform fishes were used as the outgroups for the Anguilliformes in which saccopharyngiforms constitute a derived clade. Note the extraordinary long branches within saccopharyngiforms, by far the longest within elopomorph fishes. The phylogenetic relationships presented are corroborated by extensive mitochondrial gene orders. Neocyematidae is a sister taxon to the gulper eels (Saccopharyngidae and Eurypharyngidae) and erected as a new family in accordance with gene orders depicted in Fig 7 and morphology, and the families Congridae, Colocongridae and Nettastomatidae are found to be non-monophyletic sensu current classification.
Fig 7.
Mitochondrial gene orders of “saccopharyngiform” fishes.
Highly similar gene orders are present in Neocyema, Saccopharynx and Eurypharynx compared to Cyema and the highly rearranged Monognathus, and these orders all differ from the more typical gene orders of the Serrivomeridae, Nemichthyidae, and Anguillidae and other vertebrates.