Talorchestia lakshadweepensis Trivedi, Lowry & Myers, 2020

Trivedi, Jigneshkumar N., Lowry, James K., Myers, Alan A. & Keloth, Rajmohana, 2020, Two species of Talorchestia Dana 1853 (Crustacea, Amphipoda, Talitridae) including T. lakshadweepensis sp. nov. from the Lakshadweep Islands, India, Zootaxa 4732 (2), pp. 295-306 : 299-305

Talorchestia lakshadweepensis Trivedi, Lowry & Myers sp. nov.

( Figs 1B , 6–8 )

Type Material. Male holotype male, 4.9 mm, ( ZSI, WRC-C.1911), Cheriyam Island (10°04’11’N 73°39’37’’E), sandy shore, 29 November , 2017, coll. Rajmohana Keloth . Paratype, male, 4.8 mm, ( ZSI, WRC-C.1912) same data as holotype. Paratypes 3 females, 4.4 mm; 3.3 mm; 4.3 mm; ( ZSI, WRC-C1913 ), same data as holotype .

Other material. 3 males (4.4–4.8 mm) and 26 females (6 ovigerous), (3.2–6.0 mm), LFSC.ZRC-110, same data as holotype .

Category. Mascupod.

Ecological type. Beach-hoppers (mainly coastal supralittoral/intertidal leaf-litter/wrack, non-substrate modifying talitrids).

Etymology. The species is named after union territory of Lakshadweep where its type locality Cheriyam Island is located.

Diagnostic description. Based on holotype, male, 4.9 mm, ZSI, WRC-C.1911.

Head. Eye medium (1/5–1/3 head length). Antenna 1 short, not reaching midpoint of peduncular article 4 of antenna 2. Antenna 2 shorter than half body length; peduncular articles slender; article 5 longer than article 4; peduncular articles with many robust setae; Mandible left lacinia mobilis 5-cuspidate. Maxilliped palp broad: article 2 with distomedial lobe; article 4 reduced, button-shaped or fused with article 3.

Pereon. Gnathopod 1 sexually dimorphic; parachelate; carpus posterior margin with lobe covered in palmate setae; propodus posterior margin with 1 lobe covered in palmate setae; propodus ‘subtriangular’ with well-devel- oped posterodistal lobe, palm transverse. Gnathopod 2 sexually dimorphic; subchelate; basis slender with two rows of marginal robust setae; ischium with rounded anterodistal lobe; posterior margin of merus, carpus and propodus each without lobe covered in palmate setae; merus and carpus separate; carpus reduced (enclosed by merus and propodus); propodus subovate, 1.8 × as long as wide, palm acute, lined with robust setae, with weak sinus near dactylar hinge; posterodistal surface with groove; dactylus not modified distally, blunt, shorter than posterior margin of propodus; smooth, with slight posteroproximal sinus and small projection. Pereopods 3–7 bicuspidactylate; dactyli without anterodistal patch of many rows of setae. Pereopod 4 significantly shorter than pereopod 3; carpus significantly larger than carpus of pereopod 3;dactylus thickened proximally with notch midway along posterior margin. Pereopod 5 short, less than 2/3 length of pereopod 6; dactylus long, slender. Pereopod 6 not sexually dimorphic; subequal in length to pereopod 7; basis expanded. Pereopod 7 not sexually dimorphic; basis expanded; carpus unexpanded; propodus slender.

Pleon. Pleopods 1–3 all well-developed. Epimeron 1 with 3 small robust setae on the anteroventral margin; epimera 2 and 3 ventral margin without setae. Epimeron 2 subequal in length to epimeron 3; posteroventral corner a small acute tooth. Epimeron 3 posterior margin without setae; posteroventral corner with a small acute tooth. Uropod 1 peduncle with two rows of robust setae, distolateral robust seta absent; endopod shorter than exopod, with 4 marginal robust setae in one row; exopod without marginal robust setae. Uropod 2 peduncle with marginal robust setae in 1 row; endopod with 3 lateral and 2 marginal robust setae; exopod with 2 marginal setae in 1 row; rami without apical spear-shaped setae. Uropod 3 peduncle with 11 short robust setae in 2 rows; ramus linear (narrowing distally), 3.1 × as long as broad, subequal in length to peduncle, with 1 marginal setae and 4 apical setae. Telson broader than long, tapering distally, completely cleft and apically incised, with marginal and apical robust setae, with 8 robust setae per lobe.

Female (sexually dimorphic characters). Based on paratype, female, 4.4 mm ZSI, WRC-C1913. Antenna 1 short, reaching beyond midpoint of peduncular article 4 of antenna 2. Gnathopod 1 carpus posterior margin with lobe covered in palmate setae; propodus posterior margin without lobe covered in palmate setae. Gnathopod 2 mitten–shaped; basis expanded anteromedially with 1 row of marginal robust setae; carpus well developed (not enclosed by merus and propodus), posterior lobe present, projecting between merus and propodus; propodus 2 × as long as wide, palm obtuse; dactylus shorter than palm, straight, posterior margin smooth, not modified distally.

Remarks. Talorchestia lakshadweepensis sp. nov. appears to be closely related to T. affinis Maccagno, 1936 . Specimens of T. affinis reported by Lowry & Springthorpe (2019) from Kenya measured up to 14 mm in length, while T. affinis material reported here measured up to 6.7 mm. Talorchestia lakshadweepensis sp. nov. appears to be a small species, with a maximum length of only 6.0 mm. Six females collected in the present work were ovigerous, suggesting that the small size was probably not due to immaturity. Talorchestia lakshadweepensis sp. nov. differs from T. affinis in the shape of the carpus of the male gnathopod 1, in which the posterior margin behind the posterodistal palmate lobe is swollen, whereas it is flat in T. affinis . In the male gnathopod 2, the propodus is two times as long as broad with a very oblique palm in T. Lakshadweepensis sp. nov., but in T. affinis it is only one and a half times as long as broad with a less oblique palm. The male gnathopod 2 dactylus is longer and more weakly curved distally in T. Lakshadweepensis sp. nov. than in T. affinis . The ramus of uropod 3 is subequal with the peduncle in T.lakshadweepensis , but shorter than the peduncle in T. affinis .

There are several records of Talorchestia from India; Talorchestia martensii of Chilton (1921) is considered to be an undescribed species ( Lowry & Springthorpe 2019). It has a well-developed posteroventral tooth on epimeron 3 like T. martensii , but a subtriangular propodus on gnathopod 1, and a small sinus near the dactylar margin of the palm of gnathopod 2, no distolateral robust seta on the peduncle of uropod 1 and only one row of marginal setae on the endopod of uropod 2. The T. martensii of Lyla et al. (1998) is poorly illustrated and the male gnathopod 2 is not shown. It apparently has only one row of marginal setae on the endopod of uropod 2, a character it shares with T. brucei Lowry & Springthorpe (2009) from the Northern Territory, Australia and the T. martensii of Chilton (1921) from Chilka Lake, India.

Distribution. Lakshadweep Islands, south-western India.

Figures

FIGURE 1. Talorchestia affinis Maccagno, 1936, A. male, 6.7 mm, LFSC.ZRC-110, Talorchestia lakshadweepensis sp. nov., B. male paratype, 4.8 mm, ZSI, WRC-C.1912, Cheriyam Island, Union Territory of Lakshadweep, India.

FIGURE 6. Talorchestia lakshadweepensis sp. nov., male paratype, 4.8 mm, ZSI, WRC-C.1912, Cheriyam Island, Union Territory of Lakshadweep, India.

FIGURE 7. Talorchestia lakshadweepensis sp. nov., male paratype, 4.8 mm, ZSI, WRC-C.1912, female paratype, 4.4 mm, ZSI, WRC-C.1913, Cheriyam Island, Union Territory of Lakshadweep, India.

FIGURE 8. Talorchestia lakshadweepensis sp. nov., male paratype, 4.8 mm, ZSI, WRC-C.1912, Cheriyam Island, Union Territory of Lakshadweep, India.