Two new species of Floresorchestia (Crustacea, Amphipoda, Talitridae) in Thailand

Abstract The beach-hopper and land-hopper genus Floresorchestia Bousfield, 1984 is most widespread in terrestrial and marine littoral habitats and has been recorded from the South African coasts through to tropical Indo-Pacific and Caribbean Sea. In Thailand, there is only Floresorchestia samroiyodensis Azman, Wongkamhaeng & Dumrongrojwattana, 2014 reported from the swamp of Prachuab Kiri Khan, southern Thailand. In this work, two new species of Floresorchestia from Phutsa Reservoir in Nakhon Ratchasima and the man-made swamp in Burapha University are described. The new species are characterised by the mandible left lacinia mobilis 4-dentate; the posterior margin of merus, carpus and propodus covered in palmate setae; the uropod 3 peduncle with two robust setae and the telson longer than broad. The characters of the specimens are described and illustrated in this paper. All specimens are deposited in the Princess Maha Chakri Sirindhorn Natural History Museum, Prince of Songkla University, Thailand.


Introduction
The talitrid amphipod genus Floresorchestia Bousfield, 1984 is most widespread in littoral and terrestrial habitats. They have been recorded from the South African coast through to tropical Indo Pacific and Caribbean Sea. The amphipod can be recognised from the number of stridulating organs above the ventral margin (epimera 1-3, 2 or 2-3). Members of this genus occupy a variety of habitat such as beach (beach-hoppers) or land (land-hoppers) or stream (stream-hoppers) (Lowry and Springthorpe 2015). The genus Floresorchestia has established by Bousfield (1984) for a group of amphipod species with epimeral slit. After that, Serejo (2004) proposed the classification for superfamily Talitroidea and Floresorchestia is placed into the family Talitridae, the lineage of amphipods that invaded the terrestrial habitat. The Floresorchestia has recently been revised by Lowry and Springthorpe (2015). From that, four species are redescribed based on neotypes and lectotypes newly established from this work with the description of nine new species.

Key to known Thai Species of Floresorchestia
Ecological type. Land-hoppers (truly terrestrial). Size 5.5 mm. Sexual dimorphism present.
Pereon. Gnathopod 1 sexually dimorphic; subchelate; coxa 1 smaller than coxa 2, ventral margin with six setae; posterior margin of merus, carpus and propodus each with a lobe covered in palmate setae, palmate lobes in male only; carpus 1.4 times as long as propodus, 2.6 times as long as broad; propodus subtriangular with well-de-veloped posterodistal lobe, anterior margin with two groups of robust setae, posterior margin with four robust setae, palm with seven robust setae; dactylus cuspidactylate, subequal in length to palm.
Pleon. Pleopods all well developed. Pleopod 1 peduncle without marginal setae; biramous, inner ramus not longer than outer ramus, shorter than peduncle; inner ramus with seven articles; outer ramus with seven articles. Pleopod 2 peduncle without marginal setae; biramous, inner ramus subequal to outer, shorter than peduncle; inner ramus with eight articles; outer ramus with eight articles. Pleopod 3 peduncle without marginal setae; biramous, outer ramus shorter than peduncle; inner ramus with ten articles; outer ramus with eight articles.
Uropod 1 peduncle with four robust setae, distolateral robust seta absent; inner ramus subequal in length to outer ramus, inner ramus with marginal robust setae (one row), with four marginal robust setae; outer ramus without marginal robust setae. Uropod 2 not sexually dimorphic; peduncle with three robust setae; inner ramus subequal in length to outer ramus, with marginal robust setae; outer ramus with marginal robust setae in one row, outer ramus with two marginal robust setae. Uropod 3 peduncle with two robust setae; ramus not fused to peduncle; ramus shorter than peduncle, 1.75 times as long as broad, ramus linear with three apical setae.
Telson longer than broad, apically cleft, dorsal midline half of the telson, with marginal and apical robust setae, four setae per lobe.
Female (sexually dimorphic characters). Gnathopod 1 coxa anterior margin straight; merus lacking tumescent lobe, posterior margin with five robust setae; propo-     dus without tumescent protuberance, anterior margin with two groups of robust setae; palm slightly acute, dactylus inner lateral posterior margin with one robust seta.
Gnathopod 2 mitten-shaped; posterior margin of carpus and propodus each with lobe covered in palmate setae; carpus well developed, posterior lobe projecting between merus and propodus; nearly twice as long as wide; palm obtuse, not lined with robust setae, posterodistal corner without spine; dactylus subequal in length to palm, not modified distally, blunt.
Habitat. Terrestrial, most prefer living in Typha angustifolia root near reservoir. Distribution. North-eastern Thailand. Remarks. Floresorchestia boonyanusithii sp. n. is the second land-hopper reported in Thailand. It can be distinguished from F. samroiyodensis by the characters in the above key. Additionally, this species shows the following differences: 1) the left mandible lacinia mobilis has four cusps in both male and female (vs. male 4-dentate and female 6-dentate); 2) male gnathopod 1 carpus is 2.6 times longer than broad, 1.4 as long as propodus (vs. 2 times longer than broad, 1.8 times as long as propodus); 3) male gnathopod 2 propodus 1.4 times longer than broad, palm extending 39% along posterior margin (propodus 1.8 times longer than broad, palm extending 27% along posterior margin); 4) pereopod 7 is shallow, broadly rounded (vs. rounded, produced downwards almost to merus).
Floresorchestia boonyanusithii shared several characters with F. buraphana in having a mandible left lacinia mobilis 4-dentate; posterior margin of merus, carpus and propodus covered in palmate setae; uropod 3 peduncle with two robust setae and telson is longer than broad. F. boonyanusithii differs from F. buraphana in having uropod 3 rami without marginal setae (vs rami with one marginal seta) and telson with four robust setae per lobe (vs. five robust setae per lobe).
Ecological type. Supralittoral (325 m from the Bang San Beach). Size 6.3 mm. Sexual dimorphism present.
Description. Based on male, holotype, 6.3 mm, PSUZC-CR 0312. Head. Eye large (one third of head length). Antenna 1 short, having five articles of flagellum, extending one quarter (¼) of antenna 2 peduncle article 5. Antenna 2 peduncular articles slender; article 5 longer than article 4; flagellum of 13 articles, longer than peduncle, final article minute, without apical cluster of serrate setae. Upper lip broad, deep, apex rounded. Lower lip without inner plates. Left mandible incisor 5-dentate, lacinia mobilis 5-dentate, molar strong. Maxilla 1 inner plate slender with two terminal setae; outer plate with nine serrate robust setae and with small palp, 1-articulate. Maxilliped inner plate with apical and subapical plumose setae and three large conical robust setae; outer plate with two rows of subapical setae; palp article 2 distomedial lobe well developed; article 4 reduced, button-shaped.
Uropod 1 peduncle with nine robust setae, distolateral robust seta absent; inner ramus subequal in length to outer ramus, inner ramus with marginal robust setae (one row), with three marginal robust setae; outer ramus without marginal robust setae. Uropod 2 not sexually dimorphic; peduncle with four robust setae; inner ramus subequal in length to outer ramus, with marginal robust setae; outer ramus with marginal robust setae in one row, outer ramus with two marginal robust setae. Uropod 3 peduncle with two robust setae; ramus not fused to peduncle; ramus shorter than peduncle, 2.2 times as long as broad, ramus linear with a marginal seta and three apical setae.
Telson longer than broad, apically cleft, dorsal midline half of the telson, with marginal and apical robust setae, five setae per lobe.
Female (sexually dimorphic characters). Gnathopod 1 coxa anterior margin straight; merus lacking tumescent lobe, posterior margin with five robust setae; propodus without tumescent protuberance, anterior margin with two groups of robust setae; palm slightly acute, dactylus inner lateral posterior margin with one robust seta.
Gnathopod 2 mitten-shaped; posterior margin of carpus and propodus each with a lobe covered in palmate setae; carpus well developed, posterior lobe projecting between merus and propodus; nearly twice as long as its width; palm obtuse, not lined with robust setae, posterodistal corner without spine; dactylus subequal in length to palm, not modified distally, blunt.
Habitat. Fresh water swamps in Burapha University. Distribution. Eastern Thailand.
Remarks. The characters of Floresorchestia buraphana sp. n. that separate it from F. samroiyodensis Azman et al. 2014 and F. boonyanusithii sp. n. have been given in the above key. Additionally, this species shows the following features: 1) uropod 1 peduncle with nine robust setae; 2) uropod 3 peduncle with two robust setae and rami with three apical setae and telson longer than broad, dorsal midline at least halfway, apically incised with five robust setae per lobe.
F. buraphana sp. n. appears to be closely related to F. yehyuensis, sand-hopper from Taiwan in having; 1) a mandible left lacinia mobilis 4-dentate; 2) gnathopod 1 merus, carpus and propodus each with palmate lobe and 3) uropod 3 ramus with one marginal setae. It differs however in the pereopod 4 dactylus which is thickened proximally with a notch midway along the posterior margin (similar to pereopod 3 dactylus in F. yehyensis), uropod 3 peduncle with three robust setae (with two robust setae in F. yehyensis), epimera 2 with 25 slits (33 slits in F. yehyensis) and telson longer than broad with dorsal midline half way (telson is broader than its length without dorsal midline in F. yehyensis).