Description of Floresorchestia samroiyodensis , a new species of landhopper ( Crustacea , Amphipoda , Talitridae ) from Thailand

A new species of landhopper from Thailand is described. Its main diagnostic features are its large eyes; antenna 1 short; antenna 2 slender; maxilliped palp article 4 reduced, button-shaped; mandible right lacinia mobilis 6-dentate; gnathopod 1 subchelate with palmate lobes on the carpus and propodus; gnathopod 2 subchelate; pereopods cuspidactylate, with dactylus of pereopod 4 thickened and pinched; epimera 2-3 with stridulating organ just above ventral margins; uropod 1 outer ramus with a row of 3-4 robust setae; telson apically incised.


Introduction
Members of the talitrid amphipods are known to inhabit a wide range of habitats including forests, marshes and coastal environments (Bousfield 1982).Currently there are 59 recognised talitrid amphipod genera ranging from the palustral talitrids (marsh-hoppers), beach fleas (beach-hoppers), sand hoppers and the land hoppers (Lowry and Coleman 2012).Nevertheless, the landhoppers in Southeast Asian region particularly, is as yet poorly known.Only seven species have so far been recorded in this region.The first known Southeast Asian region landhopper (Parorchestia luzonensis) was described by Baker (1915) from the summit of Mt.Maquiling, and in the same paper he described another species (Parorchestia lagunae) from the freshwater lake of central Luzon (Bay Lake), Philippines.Still in the early 20 th century, another high altitude landhopper species Parorchestia kinabaluensis, was reported from Mt. Kinabalu, Sabah (Shoemaker 1935).Bussarawich et al. (1984) recorded two unnamed species of Microrchestia and Floresorchestia from the mangrove area of Southern Thailand.While Miyamoto and Morino (2008) reported Floresorchestia anomala (Chevreux, 1901) from Malaysia.Recently, Lowry and Coleman (2012) described a new genus Curiotalitrus from rainforests in the Philippines.In this paper, we describe a 6-dentate cuspidactylate terrestrial amphipod discovered from a swamp forest in central Thailand.

Materials and methods
This study is based upon material collected from leaf litter of Khao Sam Roi Yod National Park (Fig. 1), Inner Gulf of Thailand in July 2011.Samples were collected using hand-nets and were then carefully transferred into plastic containers and fixed in 10% buffered formalin.In the laboratory, amphipod specimens were sorted out and stored in 70% alcohol.The animals were then examined under a compound microscope and later selected for dissection.The appendages of the dissected specimens were examined and figures were produced using a Leica DMLB light microscope with a camera lucida.All illustrations were digitally 'inked' following Coleman (2003).Setal and mouthpart classifications following Watling (1989).Figure legend: A, antenna; G, gnathopod; HD, head; LL, lower lip; MD, mandible; MX, maxilla; MP, maxilliped; P, pereopod; Pl, pleopod; T, telson; U, uropod; UR, urosome; UL, upper lip; R, right; L, left; ♂, male; ♀, female.Type material is deposited at Prince of Songkla University Zoological Collection with the prefix PSUZC for museum numbers and the Universiti Kebangsaan Malaysia Muzium Zoologi with the prefix UKMMZ for museum numbers.Diagnosis: Antenna 1 having 3 short articles of flagellum, reaching ¼ of peduncular article 5 of antenna 2; antenna 2 bearing more than 12 articles of flagellum; anterior coxal lobe of pereopod 6 not well developed; Mandible (female) right lacinia mobilis 6-dentate.Maxilliped palp  article 2 distomedial lobe well developed, article 4 reduced, button-shaped.Gnathopod 1 parachelate; posterior margin of carpus and propodus each with lobe covered in palmate setae in male, posterior margin of merus, carpus and propodus each without lobe covered in palmate setae in female; palm slightly obtuse in male.Gnathopod 2 subchelate in male; mitten-shaped in female.Pereopods 2-4 coxae as wide as deep.Pereopods 3-7 cuspidate.Pereopods 6-7 longer than pereopods 3-5, with slender setae along posterior margin of dactyli.Pereopod 6 basis expanded in male.Epimera 2-3 with stridulating organ just above ventral margins (also presenting males where known).Pleopods well developed, similar in form and length; Uropod 1 peduncle distolateral robust seta present; inner ramus with marginal robust setae.Uropod 2 inner and outer rami with marginal robust setae.Uropod 3 ramus subequal in length to peduncle with 2 peduncular robust setae and 2 apical ones on ramus.Telson apically incised with marginal and apical robust setae, with 5 robust setae per lobe.
Upper lip broad, deep, apex rounded and densely pilose.
Lower lip broad, densely pilose on inner shoulder, distally in central trough and outer margin; lateral lobes long.
Maxilla 1, inner plate slender with 2 terminal setae; outer plate with 9 articulating seta, medially with a row of 8 articulating seta.
Maxilla 2 plates narrow, inner plate slightly shorter than outer; inner plate with ca.19 subapical robust setae, 1 plumose robust seta located at inner corner; outer plate with ca.27 subapical robust setae more or less in 2 rows.
Maxilliped inner plate distally rounded, with apical and subapical plumose setae and 2 large conical robust setae; outer plate apically blunt, with a group of subapical setae.
Maxilliped palp broad; article 1 with 2 marginal and submarginal setae; article 2 with well-developed medial lobe, inner margin scalloped, with a row setae; outer margin of article 3 with several long setae, article 4 visible with robust setae apically.
Uropod 1 peduncle longer than rami, peduncle bearing 1 outer marginal robust setae and 4 inner marginal robust setae; rami slender, subequal in length, outer ramus lacking marginal robust setae, inner ramus with 4 robust marginal setae, both with large apical and subapical robust setae.
Uropod 2, peduncle subequal to rami in length; peduncle bearing 1 outer marginal and 3 inner marginal robust setae; rami slender, subequal in length, outer ramus and inner ramus with 2 marginal robust setae, apical robust setae with tapering acute tips.
Telson as broad as long, and apically shallow incised; each side with several robust setae (normally with 5-6).
Remarks.The new species is characterized by having the mandibular left lacinia mobilis 6-dentate; dactylus of pereopod 4 thickened and pinched, and also shows the following features: large eyes; antenna 1 short; antenna 2 slender; maxilliped palp article 4 reduced, button-shaped; gnathopod 1 subchelate with palmate lobes on the carpus and propodus; gnathopod 2 subchelate; pereopods cuspidactylate; epimera 2-3 with stridulating organ just above ventral margins; uropod 1 outer ramus with a row of 3-4 robust setae; telson apically incised.Individuals belonging to this new species are found underneath the moist environment of the forest leaf litter.
The species of Floresorchestia are known to be tropical and widespread which is, distributed in terrestrial habitats of rain forests of the tropical Indo-Pacific (Bousfield 1984) and also in the Caribbean Sea (Lowry and Springthorpe 2009).Bousfield (1984) documented Floresorchestia for a group of described species with unique stridulating organs on the epimera.These epimeral slits are considered to be a powerful autapomorphy for Floresorchestia (Lowry & Bopiah, 2012) and they are found in various combinations: epimera 1-3; epimera 2-3 (most common); epimeron 2; epimeron 3.Recently Miyamoto and Morino (2008) and Lowry and Springthorpe (2009) have both discussed the morphology of the genus, refining characters and describing additional new species that brings a total of 16 valid species.
Floresorchestia samroiyodensis sp.n. shares several unique characters with F. ancheidos (K.H. Barnard, 1916) and F. guadalupensis (Ciavatti, 1989) in having the stridulating organs on epimera 2-3 and palmate lobes on the carpus and propodus of gnathopod 1. However the new species differs from any other members of Floresorchestia in its more developed dentitions (6-dentate) of lacinia mobilis on the female right mandible, as well as in having two rows of spine-like teeth in outer plate of maxilla 1, and the telson with 4-5 setae per lobe.

Figure 1 .
Figure 1.Map of the Inner Gulf of Thailand and the collection site (Sam Roi Yod National Park).

Type locality: Khao
Sam Roi Yod National Park, Sam Roi Yod district, Prachuap Khiri Khan Province, Thailand.