Holotype, female, 10.6 mm, PSUZC-CR-0275, leaf litter of Khao Sam Roi Yod National Park, 12°14’36.93” N, 99°55’57.55” E, hand net, Pongrat Damrongrojwattana, 1 July 2011. Paratypes: 2 males, 13 females, 3 juveniles UKMMZ-1476, same station data.

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

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.

(Based on holotype female, 10.6 mm, PSU-CR-0275)

Body compressed laterally, dorsal surface smooth. Head, height subequal to length. Eyes large, (greater than 1/3 head length). Antenna 1 short, ca. 1/3 of antenna 2; flagellum with 4 articles, shorter than peduncle; peduncular articles subequal in length. Antenna 2 peduncular articles narrow; article 5 longer than article 4; flagellum of 15 articles, longer than peduncle.

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.

Left mandible incisor 5-toothed; molar process strong, with 15 striate (Sexually dimorphic in males; left lacinia mobilis with 4 teeth and right with 3 teeth). Right mandible incisor 6-toothed; molar process strong, with 16-17 striate.

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.

Coxae 3-4 of medium depth, subquadrate, spinose lower margin slightly curvy or almost flat, posterior process small and acute; coxa 5 deep, subequal to depth of coxa 4, anterior lobe large, posterior and ventral margins spinose, posterior lobe small; coxa 6 depth subequal to length, anterior lobe small, margin rounded distally; coxa 7 not deeper than coxa 6, gently curving below, weakly spinose.

Gnathopod 1, coxa anterior margin straight, ventral margin with 5 setae; basis straight almost parallel-sided; merus lacking tumescent lobe, posterior margin with 5 robust setae; carpus without tumescent protuberance; propodus without tumescent protuberance, anterior margin with a row of 7–8 robust setae, posterior margin with 6 robust setae; dactylus, 4 simple setae on anterodistal corner, inner lateral posterior margin with 1 robust seta, slightly acute.

Gnathopod 2 coxa as wide as deep with posterior process, convex ventral margin with 6 fine setae; basis expanded anteroproximally, posterior margin slightly straight; ischium subequal to merus in length; carpus elongate; propodus with posterodistal tumescent protuberance elongated distally, scabrous region from posteroproximal end to posterodistal end, outer lateral surface with several serrate setae, palm margin short, anterodistal corner with 3–4 simple setae; dactylus curved.

Sexual dimorphism present in gnathopods.

Gnathopod 1 of male short; basis strong, anterior margin with 4 setae and posterior margin with 2 setae; merus without posterior tumescent lobe; carpus deep, with posterior tumescence lobe; propodus slightly curved, shorter than carpus, posterodistal tumescent lobe large; subchelation strong, dactylus not exceeding palm and slightly obtuse.

Gnathopod 2 of male strongly subchelate, larger than 1; basis, anterior margin smooth, widened distally; ischium lobed anteriorly; merus subequal in length with ischium; propodus long ovate, bearing a row of small robust setae near dactylar hinge; palm oblique; dactylus curved, attenuated distally with smooth inner margin.

Pereopods 3–7 cuspidactylate. Pereopod 3 coxa subquadrate with posterior process, ventral margin slightly convex; basis longest; ischium shortest, anteroproximal margin notched; merus longer than carpus, anterior margin slightly convex, posterior margin straight; carpus anterior and posterior margins parallel; propodus slender, longer than carpus; dactylus subequal to ischium in length.

Pereopod 4 similar to pereopod 3, shorter, coxa wider than long, with posterior process, ventral margin straight; basis longest, convex; ischium shortest, anteroproximal margin notched; merus longer than carpus, anterior margin convex, posterior margin straight; carpus short; propodus slender, subequal to merus; dactylus posterior nail base with 1 simple seta.

Pereopod 5 coxa bilobed, anterior lobe larger than posterior lobe; basis oval; ischium shortest, posteroproximal margin notched; merus shorter to carpus in length, anterior margin straight, posterior margin slightly convex; carpus both margins parallel; propodus slender; dactylus short.

Pereopod 6 coxa bilobed, anterior lobe much smaller than posterior lobe; basis oval, anterior margin with short robust setae; ischium shortest, posteroproximal margin notched; merus slightly shorter than carpus in length, anterior margin straight, posterior margin slightly convex; carpus both margins parallel; propodus slender, longest; dactylus short.

Pereopod 7 coxa small, subquadrate; basis oval, posterodistal lobe broader than pereopod 5–6; ischium shortest; merus slightly shorter in length to carpus, anterior margin straight, posterior margin slightly convex; carpus anterior and posterior margins parallel; propodus slender, longest; dactylus narrow.

Epimeral plates, plate 1 smoothly rounded anterodistally and distally, posterodistal corner slightly protruded, hind margin slightly sigmoid; plate 2 slightly longer than plate 3, anterodistally rounded with a row of slits (16-21 slits) along ventral margin, posterodistal corner produced; plate 3 also with a row of slits (13-15 slits) along ventral margin and posterodistal corner produced.

Pleopods well developed, subsimilar in form and length. Peduncles sublinear; all pleopods biramous. Rami shorter than peduncles, with distinct segmentation.

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.

Uropod 3, peduncle expanded proximally, narrowing distally, longer than deep, 2 robust setae set submarginally; ramus slightly shorter than peduncle, tapering distally, bearing 2robust setae apically and another 2 along the margin.

Telson as broad as long, and apically shallow incised; each side with several robust setae (normally with 5–6).

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.