Discovery of a new genus and species of dogielinotid amphipod (Crustacea: Amphipoda: Dogielinotidae) from the Nipa palm in Thailand, with an updated key to the genera

During a scientific survey, a new genus of the dogielinotid amphipoda was found in the Nipa palm (Nypa fruticans) in Bang Krachao Urban Oasis, Samut Prakan Province, Thailand. We placed this new genus, Allorchestoides gen. nov., within the family Dogielinotidae. The new taxa can be easily distinguished from the remaining genera by differences in the incisor of the left and right mandibles, apical robust setae of the maxilla 1, and the large coxa and strong obtuse palm in the female gnathopod 1. The type species of Allorchestoides gen. nov., Allorchestoides rosea n. sp., is described here in, with an updated key to the genera of the family Dogielinotidae.

The family Dogielinotidae is distributed in the temperate zones in the Pacific Ocean and tropical zones in the Indian Ocean in shallow water beaches (Derjavin [7]; Kamihira [8]; Barnard & Karaman [3]; Lazo-Wasem & Gable [9]; Odelvig [10]; Serejo [5]; and Bousfield [11] The family was established by Gurjanova [12] in 1953, together with the monotypic genus Dogielinotus, based on the species Dogielinotus moskvitini (Derzhavin, 1930). In 2004, Serejo [5] divided the family Dogielinotidae into three subfamilies: Dogielinotinae, Hyalellinae, and Najaninae. Recently, a revision by Lowry and Myers in 2013 [6] raised these subfamilies to the family level. Until now, 37 species belonging to 10 genera have been reported in the family Dogielinotidae [13]. During a scientific survey, however, a new member of the family Dogielinotidae was discovered in the Nipa palm (Nypa fruticans) in Bang Krachao Urban Oasis, Samut Prakan Province, Thailand, and it is not assignable to any previously known genera of Dogielinotidae. In the present study, we describe and illustrate a new genus and a new species.

Material and methods
Amphipods were collected from Nipa palm leaves in the Bang Krachao Estuary, near the mouth of the Chao Phraya River mouth (13˚41'47.4"N 100˚33'52.4"E) (Fig 1). The leaves were torn, and the amphipod specimens inside were sorted out and fixed in formalin for one week; then, they were stored in 70% ethanol. In the laboratory, the specimens were transferred from ethanol into glycerol for morphological study. Drawings were made using a drawing tube attached to an Olympus CH30 light microscope. The pencil drawings were scanned and digitally inked using a WACOM bamboo CTH-970 graphics board via Adobe Illustrator CC 2017, following the method described in Coleman [14]. The setae description was following the work of Garm [15]. The specimens were deposited in the Prince of Songkla University Zoological Collection (PSUZC).

Ethics statement
This study was carried out in strict accordance with the recommendations in Animal Care & Use Guidelines of Institutional Animal Care and Use Committee of Burapha University (IACUC BUU). Amphipods were prior anesthetized with ice, then fixed in 10% formalin and finally preserved in 70% ethanol. The study area is a public area which no specific permissions were required for this location. All efforts were made to minimize suffering and habitat destruction. This work did not involve endangered or protected species.

Nomenclatural acts
The electronic edition of this article conforms to the requirements of the amended International Code of Zoological Nomen clature, and hence the new names contained herein are available under that Code from the electronic edition of this article. This published work and the nomenclatural acts it contains have been registered in ZooBank, the online registration system for the ICZN. The ZooBank LSIDs (Life Science Identifiers) can be resolved and the associated information viewed through any standard web browser by appending the LSID to the prefix "http://zoobank.org/". The LSID for this publication is: urn:lsid:zoobank.org: pub:6313CE72-9F23-47C6-9724-879AF0E570B0. The electronic edition of this work was published in a journal with an ISSN, and has been archived and is available from the following digital repositories: PubMed Central, LOCKSS. Diagnosis: Male. Mouthparts, mandible, right incisor process four dentate; left incisor process six dentate; accessory setal row present; molar triturative. Maxilla 1 outer plate with six distal setal-teeth. Maxilla 2, inner plate with an enlarged proximal seta; outer plate subequal to inner plate in length. Maxilliped, outer plate shorter than article 2 of maxilliped palp; palp welldeveloped, dactyl unguiform. Coxal plates 1-4 deep, subrectangular; coxal plate 1-3 posterior marginal cusp absent. Gnathopods sexually dimorphic. Male gnathopod 1 weakly chelate; carpal lobe well-developed; palm slightly protruding at palmar corner, dactylus fitting palm. Gnathopod 2 propodal palm smoothly concave, interior margin lined with pappose setae. Epimeral side plates ordinary, plate 2 deepest. Pleopods peduncle with 2 small retinacula;
Type species: Allorchestoides rosea, new species, here designated. Etymology: The specific name, Allorchestoides, alludes to fact that the new genus is allied to Allorchestes Dana, 1849. The gender is feminine as the gender adopted by its original authors.
Remarks: The new genus is similar to Allorchestes Dana, 1849, from the north and south Pacific [14], because it has a dactylus of maxilliped unguiform; carpus of male gnathopod 2 lobate, projecting between the merus and propodus; uropod 3 uniramus; and telson cleft that is halflength. However, the 1-articulate maxilla 1 palp in Allorchestes is reduced and tiny, not reaching the base of the setal-teeth of the outer lobe, while that of Allorchestoides gen. n. is absent ( Table 1).
The Allorchestoides gen. n. shares some characteristics with Exhyalella Stebbing, 1917, from the Indian Ocean, because it has a vestigial maxilla 1 palp and uropod 3 uniramus. However, the current genus differs from Exhyalella because the carpus of the male gnathopod 2 is well-developed, the posterior carpal lobe is present (vs. carpus reduced, posterior carpal lobe absent), and the telson cleft is half-length (vs. entire) ( Table 1).
The new genus can be easily distinguished from the remaining genera: 1) its right and left mandible has a 4-toothed and 6-toothed incisor, respectively; 2) the outer plate of the maxilla 1 contains 6 apical robust setal-teeth, whereas other talitroideans contain 9 apical robust setalteeth; and 3) the peduncle and ramus of the uropod 3 are lined with robust setae and pappose setae. Moreover, the female of this new genus is characterized by having a large coxa 1 strongly produced posterodistally, and a gnathopod 1 propodus palm strongly obtuse with long oostegites and an apex sharply rounded with sparse setae.
The amphipod species is categorized into Dogielinotidae Gurjanova, 1953, as 1) antenna 1 is longer than the peduncle of antenna 2, 2) it has a mandibular molar palp vestigial and molar trituative, 3) article 4 of the maxilliped palp is well-developed, and 4) the male gnathopod 2 exhibits sexually dimorphic and a telson clef that is half of the length.
The new genus could be identified using the following updated key to include Allorchestoides gen. n.
Key to the genera of Dogielinotidae Etymology: This species is named after the distinct reddish color while the amphipod alive (Fig 2).

Discussion
All of the species of the family Dogielinotidae have been known to be marine members, and they are free-living in shallow water and shallow water and sand bottom [16]. The   Allorchestoides gen. n. is the only genus in this group that lives in brackish water and is associated inside a submerged Nipa palm trunk.
Some modifications of their morphological characters would have them fit with the habitat of Pseudamphithoides incurvaria (Just, 1977), a species of house-building ampithoids amphipods that freely moves among hydroids and algae with their house by using prehensile pereopods 5-7 [17]. The prehensile dactyl of Allorchestoides rosea n. sp. might be used for grasping and moving among the fiber of the Nipa palm (S1 Video). Moreover, the pappose setae existing on the antennae, gnathopods, mandible, maxillae, maxilliped, and pereopods seem to be used for grooming food particles. Garm [15] described the pappose setae as the setae that contain long, well-developed setules scattered randomly along the total length of the shaft of the setae. The setae are always found laterally on the mouthparts, exopods, and endopods of the maxillae and maxilliped. That work focused on the setae that existed on the mouthparts and concluded that the pappose setae on the mouthparts of seven species of decapod function by acting as setal barriers, detecting current direction, and filtering. The setae were also present on the mandibular palp of the shrimp, Penaeus monodon Fabricius, 1798 where the roof of the feeding area was formed. In talitroidean amphipods, there is a variety of accessory grooming structures, i.e., setae, scale, and spine found on both gnathopods 1 and 2. In the aquatic group, the accessory grooming structure exist only on the gnathopod 1, and the gnathopod 2 is used for carrying [15,18].
According to observations conducted in the laboratory, the amphipod feeds mainly on the palm tissue, which the food item present in stomach. The feeding procedure starts from the creation of the feeding current along the ventral part by pleopods, followed by grasping of the food items by the gnathopod 2 and grooming by the gnathopod 1 and antenna 2. The pappose setae occurring on antennae 1 and 2 and gnathopods 1 and 2 may be necessary for grooming to live among fiber of Nipa palm. Further investigations about the feeding behavior and feeding ecology of this group are needed to obtain a deeper understanding.