Talorchestia seringat, Azman, B. A. R., 2017

Azman, B. A. R., 2017, The talitrid amphipod genus Talorchestia from the South China Sea to the Indonesian Archipelago (Crustacea, Senticaudata), Zootaxa 4319 (3), pp. 401-434 : 418-422

Talorchestia seringat sp. nov.

( Figs 13–15 )

Type material. Holotype, male, ~ 8.8 mm, ZRC 2016.0099 (SEM pin and 4 stubs), supralittoral, man-made lagoon Lazarus Island , Singapore (1°13.580'N 103°51.152'E), living under light cover of sticks and plastic on white fine sand beach, D. Fautin, 24 May 2013 . Paratypes: female, ZRC 2016.0100 (wet specimen and SEM stub); 15 males and 28 females, ZRC 2016.0101 , same data as holotype.

Additional material examined. Many specimens, man-made lagoon, Lazarus Island, Singapore (1°13.580'N 103°51.152'E), living under light cover of sticks and plastic on white fine sand beach, J.K. Lowry, 21 May 2013, SS-0128 (SW-11) . 28 specimens, south-east corner of Lazarus Island , Singapore (1°12.870'N 103°51.045'E), living under light cover of sticks and plastic on coarse sand beach backing on to forests, J.K. Lowry, 21 May 2013, SS- 0 136 (SW-9) . 28 specimens, beach with seawall immediately behind small mangrove patch, south-west corner of man-made lagoon just north of the military facility, St Johns Island , Singapore (1°13.033'N 103°51.068'E), S. Ahyong, 22 May 2013, SS-1671(SW-21).

Type locality. Sand beach in man-made lagoon, Lazarus Island, Singapore (1°13.508'N 103°51.152'E).

Habitat. Living under light cover of sticks and plastic on white fine sand beach.

Etymology. Named for the original small island subsumed by the northern end of Lazarus Island.

Description. Based on Holotype, male, ~ 8.8 mm, ZRC 2016.0099.

Head. Antenna 2 length more than half but not exceeding body length (about 60%); peduncular articles with marginal row of robust setae, with many small robust setae, article 5 much longer than article 4; flagellar articles final article large, cone-shaped forming a virgula divina, with apical cluster of 'imbricated' setae. Labrum upper lip with apical setal patch; epistome without robust setae, without many pores. Mandible left lacinia mobilis with 5 cusps. Labium distolateral setal tuft absent; without inner plates. Maxilla 1 with small palp, 2-articulate. Maxilliped palp article 2 distomedial lobe well developed; article 4 fused with article 3.

Pereon. Gnathopod 1 coxa smaller than coxa 2; carpus 1.8 × as long as propodus, 2.5 × as long as broad; propodus slightly tapering distally, anterior margin with 6 groups of robust setae (about 21 robust setae), about 3 × as long as broad; dactylus longer than palm, with anterodistal denticular patch. Gnathopod 2 sexually dimorphic; basis anterior margin smooth, basis slender; ischium with subquadrate anterodistal lobe, with distally rounded anterodistal lobe on medial surface; carpus triangular, reduced (enclosed by merus and propodus), posterior lobe absent, not projecting between merus and propodus; propodus 1.6 × as long as wide, palm reaching about 50% along posterior margin, smooth, without protuberance near dactylar hinge, lined with robust setae, posteromedial surface of propodus with groove; dactylus subequal in length to palm, curved, without anteroproximal bump, posterior margin sparsely lined with small robust setae, with shallow posteroproximal sinus. Pereopods 2–4 coxae deeper than wide. Pereopods 3–7 dactyli without anterodistal patch of many rows of tiny setae. Pereopod 4 significantly shorter than pereopod 3; carpus significantly shorter than carpus of pereopod 3. Pereopod 5 propodus distinctly longer than carpus. Pereopod 6 coxa posterior lobe medial view posteroventral corner rounded, posterior margin oblique to ventral margin, posterior lobe with ridge, posterior lobe with 5 or more marginal setae. Pereopod 7 basis lateral sulcus present, slightly pronounced, posterior margin with numerous small robust setae, small posterodistal lobe present, shallow, narrowly rounded; distal articles (merus and carpus) slender; merus posterior margin straight.

Pleon. Epimeron 1 with 2 robust setae along ventral margin. Epimeron 3 posterior margin minutely serrate, with setae (tiny), posteroventral corner with small subacute tooth. Uropod 1 peduncle with 14–15 robust setae, distolateral robust seta small (less than 1/4 length of outer ramus); inner ramus subequal in length to outer ramus, with 5 lateral, and 5 medial marginal robust setae; outer ramus without marginal robust setae. Uropod 2 peduncle with 10 robust setae; inner ramus subequal in length to outer ramus, 4 lateral and 3 medial marginal robust setae. Uropod 3 peduncle with 5–6 robust setae; ramus not fused to peduncle, ramus 2.9 × as long as broad, ramus linear (narrowing). Telson longer than broad, dorsal midline complete, with 8 setae per lobe.

Female (sexually dimorphic characters). Based on paratype, female, ZRC 2016.0100. Gnathopod 1 coxa subequal in size to coxa 2; carpus 1.5 × as long as propodus, 3.1 × as long as broad; propodus subrectangular, anterior margin with 5 groups of robust setae. Gnathopod 2 basis strongly expanded; ischium without lobe on anterior margin, without anterodistal lobe on medial surface; carpus well developed (not enclosed by merus and propodus), posterior lobe present, projecting between merus and propodus; propodus twice as long as wide, palm nearly straight, with cuticular surface, without cuticular patch at corner of palm; dactylus slightly curved, posterior margin smooth. Uropod 3 ramus with 2–3 marginal robust setae.

Remarks. Talorchestia seringat and T. sipadan are very similar species. They differ in a number of small ways: T. seringat has 5 cusps on the lacinia mobilis (6 in T. sipadan ); the gnathopod 1 propodus is longer and more slender (3 × as long as broad), broader and shorter (2.2 × as long as broad) in T. sipadan ; the palm of the propodus on gnathopod 2 extends farther down the posterior margin (up to 56¾ in T. seringat and about 52¾ in T. sipadan ); telson longer than broad (as long as broad in T. sipadan ).

It is possible that the two species might be synonymous but until there are more collections for study, particularly from the west coast of Kalimantan, this is a moot point. Talorchestia seringat is only known from Singapore at the tip of the Malaysian Peninsula in the south-western South China Sea and T. sipadan is known only from Sipadan Island off the north-western coast of Sabah in the Celebes Sea.

Distribution. Singapore. Lazarus Island (this study)

Figures

FIGURE 13. Talorchestia seringat, male, holotype, ~ 8.8 mm, ZRC 2016.0099, Lazarus Island, Singapore. Scale lines for MD, MP represent 0.1 mm, T, U 3 represents 0.2 mm, remainder represent 0.5 mm.

FIGURE 14. Talorchestia seringat, male, holotype, ~ 8.8 mm, ZRC 2016.0099, paratype, female, ZRC 2016.0100, Lazarus Island, Singapore. Scale lines represent 0.5 mm.

FIGURE 15. Talorchestia seringat, male, holotype, ~ 8.8 mm, ZRC 2016.0099, Lazarus Island, Singapore. Scale lines represent 0.5 mm.