Polyonyx biunguiculatus ( Dana, 1852 )

Polyonyx biunguiculatus ( Dana, 1852) View in CoL

( Figs. 2B View Figure 2 , 4 View Figure 4 )

Porcellana biunguiculata Dana, 1852: 411 [type locality: Lifou Island, Loyalty Islands, by neotype selection ( Osawa, 2007)]. — Dana, 1855: pl. 26, fig. 1a–d.

Polyonyx biunguiculatus View in CoL : Stimpson, 1858: 229 — Miers, 1884: 559 (in part). — Johnson, 1970: 34. — Osawa, 2007: 31 View Cited Treatment , figs. 9, 10. — Poupin et al., 2013: 24, fig 11A. — Prakash et al., 2013b: 1517 (checklist). Polyonyx parabiunguiculatus Yang, 1996: 262 View in CoL , 268,

fig. 5.[ type locality:Nansha Islands, South China Sea].? Porcellana biunguiculata : Haswell, 1882: 147.? Polyonyx biunguiculatus View in CoL : Ortmann, 1894: 30. — Southwell, 1906: 219. — Haig, 1983: 286. — Haig, 1992: 320, fig. 16. Polyonyx tuberculosus : Zehntner, 1894: 184.? Polyonyx tuberculosus : Rathbun, 1924: 31, pl. 1, fig. 7. Not Polyonyx biunguiculatus View in CoL : Gordon, 1935: 10, fig. 5b, d. — Miyake, 1942: 371, figs. 30–32. — Miyake, 1943: 144, fig. 60. — Johnson, 1958: 105, fig. 3. — Haig,1964: 377 (in part).— Haig, 1965: 112. — Haig,

1979: 130, figs. 16–19. — Yang and Naiyanetr, 1997: 7, fig. 4A–E. [= Polyonyx similis Osawa, 2015 ].

Material examined. 4 males (2.1–2.4 × 2.5–2.8 mm) ( IO /SS/ANO/00178), Andaman Sea , off Little Andaman Island, India, FOR/ V “Sagar Sampada” station 38806, 10.72°N 92.72°E, 53 m, chain dredge, 10.viii.2019, coll. V. P. Padate GoogleMaps . 1 male (3.3 × 3.6 mm) ( IO /SS/ANO/00179), Andaman Sea , off Great Nicobar Island, India, FOR/ V “Sagar Sampada” station 38818, 6.64°N 93.82°E, 56 m, chain dredge, 16.viii.2019, coll. V. P. Padate GoogleMaps .

Diagnosis. Carapace transversely subrectangular in general outline; dorsal surface gently convex from side to side, glabrous, pitted; rostrum moderately broad, trilobate in frontal view, median lobe bluntly triangular, overreaching triangular lateral lobes ( Fig. 4A, B View Figure 4 ). Thoracic sternite 3 anterior margin nearly straight, lateral lobes bluntly produced; sternite 4 with anterior margin gently concave ( Fig. 4C View Figure 4 ). Cheliped carpus slightly convex on dorsal surface, extensor margin convex, dorso-f lexor margin gently concave, smooth; palm inf lated, smooth on dorsal surface, flexor margin blunt, extensor margin with low tuberculate ridge extending from distal half of palm to distal tip of fixed finger; dactylus with longitudinal ridge composed of small tubercles along posterior margin of dorsal surface ( Fig.4E View Figure 4 ). Dactyli of ambulatory legs each terminating in weakly curved, bifurcate claw, flexor claw stouter and shorter than extensor claw; flexor margin with 2 small corneous spines ( Fig. 4F View Figure 4 ).

Taxonomic remarks. Based on the present specimens, a short diagnosis of Po. biunguiculatus is provided above because the species is recorded from Indian waters for the first time. Polyonyx biunguiculatus is distinguished from its closest congener Po. similis by the narrower median rostral lobe, absence of flattened tubercles on the distal dorso-anterior surface of the cheliped palms and dense tuft of plumose setae on the ventroproximal cutting region of the dactylus of male larger cheliped, and the presence of a pair of gonopods on the male second abdominal segment ( Osawa, 2015). In live coloration, the present specimens resembled the material of Po. biunguiculatus from Mayotte, southwestern Indian Ocean, provided by Poupin et al. (2013, fig. 11A).

Distribution. Red Sea, eastern coast of Africa, Madagascar and neighboring islands, Mayotte and Glorioso Islands, Réunion, Seychelles, Moluccas, Australia, Hong Kong, Nansha Islands in the South China Sea, New Caledonia, Loyalty Islands; 12–120 m in bathymetric range ( Haig, 1964; 1983; Osawa, 2007; Poupin et al., 2013; present study)( Fig. 1 View Figure 1 ). This is the first record of P. biunguiculatus from Indian waters.