Maeropsis paphavasitae and Rotomelita longipropoda, two new species (Crustacea, Amphipoda) from Lower Gulf of Thailand

Abstract Two new species of maerid and melitid Amphipoda, Maeropsis paphavasitae and Rotomelita longipropoda, respectively, collected from a seagrassbed of the Lower Gulf of Thailand, are described. Maeropsis paphavasitae is characterized by it seven teeth on the palm of gnathopod 2 and Rotomelita longipropoda can be recognized by its long gnathopod 1 propodus. Their characters are described and illustrated. All specimens are deposited at Princess Maha Chakri Sirindhorn Natural History Museum, Prince of Songkla University, Thailand and the Museum für Naturkunde, Berlin.


introduction
The Gulf of Thailand contains many seagrass beds on the coast both the mainland and the islands along the gulf. There are 12 species of seagrass reported from this area. The seagrass habitats in Thailand have been investigated since 1902, covering various topics from both fauna and flora (Prathep et al. 2010). However, only one contribution deals with gammaridean amphipods, Cheiriphotis trifurcata was report (Wongkamhaeng et al. 2012). In this study, we describe the two new gammaridean species Maeropsis paphavasita sp. n. and Rotomelita longipropoda sp. n. , both of which were found in the seagrass. The discovery of them represents the first record of these two genera in South China Sea. Figures and descriptions of both species are provided.

Material and methods
Amphipods were collected using a 20×20cm 2 Ekman's grab in the mix of species seagrass beds of Talet Bay and Phangan Island ( Figure 1).The sites were visited at low tide and the specimens were collected from the subtidal zone (2-5 m). The sediment was sieved with a 0.5 mm sieve. Amphipod specimens were sorted out and preserved in 70% ethanol. In the laboratory, the animals were examined using a compound microscope and later selected for dissection. The appendages were examined and figures were drawn using an Olympus CH30 light microscope with a camera lucida. The following abbreviations are used : A, antenna; G, gnathopod; HD, head; LL, lowerlip; MD, mandible; MX, maxilla; MP, maxilliped; P, pereopod; Pl, pleopod; T, telson; U, uropod; UR, urosome;UL, upperlip; r, right;l, left; ♂, male; ♀, female. The type material of the new species is deposited at Prince of Songkla University Zoological Collection (PSUZC) and the Museum für Naturkunde, Berlin (ZMB).
Female. (sexually dimorphic characters). No sexual difference.   Etymology. The species is named in honor of Associate Professor Nittharatana Paphavasit of Chulalongkorn University, Thailand who contributed to the knowledge on seagrass habitats in Thailand.
Remarks. Maeropsis paphavasitae sp. n. is very similar to Maeropsis serratipalma (Nagata, 1965) in the palm of gnathopod 2, which is transverse with 6 blunt teeth and a large defining tooth in both species. But the new species can be distinguished from M. serratipalma by the following characters: gnathopod 1 palm without clear defining palmar corner; gnathopod 2, merus not produced into a posterodistal tooth (vs. produced); propodus of gnathopod 2 subtriangular (vs. subrectangular), palm inner surface with 1 subposterodistal robust seta (vs. without); dactyli of pereopods 3-7 curved and smooth (vs. bearing two minute teeth); uropod 3 inner ramus with only 1 proximal seta (vs. armed with several marginal robust setae) and telson longer than broad (vs. broader than long).
Etymology. The specific name "longipropoda" is from latin 'longi = long' and 'propoda = propodus', referring to the relatively long propodus of male gnathopod 2 compared to congeners.
However, the new species can be easily distinguished from its congeners by having eyes (vs. lacking eyes in R. lokoa and R. ana); antenna 1 peduncle without robust setae (vs. with 2 robust setae on ventroproximal margin in R. lokoa and R. ana); male gnathopod 2 with relatively long propodus (2.7 times as long as carpusvs, 1.6 times in the two other species) and the uropod 3 rami are shorter (2.2 times as long as peduncle) compared to the other two species (3.3 times as long as peduncle).
In terms of ecology Rotomelita, Nainalao and Tegano are recorded from fresh to brackish water (Barnard 1977;Bousfield 1971 andLowry andSpringthorpe, 2009) while R. longipropoda was collected from seagrass beds in a salinity range of 28-32 ppt. However, there is a small creek located 1 km northern of seagrass patch. The amphipods also can be considered as a brackish species. It is the first record of this genus from West Pacific.