Andamanium, Naruse & Ng, 2020

Naruse, Tohru & Ng, Peter K. L., 2020, Revision of the sesarmid crab genera Labuanium Serène and Soh, 1970, Scandarma Schubart, Liu and Cuesta, 2003 and Namlacium Serène and Soh, 1970 (Crustacea: Decapoda: Brachyura: Sesarmidae), with descriptions of four new genera and two new species, Journal of Natural History (J. Nat. Hist.) 54 (7 - 8), pp. 445-532 : 503-504

Genus Andamanium gen. nov.

Type species

Sesarma thelxinoe De Man, 1908 , by present designation. Gender neuter.

Included species

Andamanium thelxinoe ( De Man, 1908) , comb. nov.

Diagnosis

Carapace squarish, wider than long; lateral margins subparallel, with 1 distinct and 1 feeble epibranchial teeth behind external orbital angle; dorsal surface gently convex, regions weakly defined. Front deflexed at anterior margin of postfrontal lobes, distally recurved, directed anteroventrally; frontal margin straight in anterior view, overhanging onto antennular septum and fossae. Two pairs of postfrontal lobes present. Antennular septum wide, short. Orbit, in dorsal view, tilted J-shaped, median part of supraorbital margins oblique; inner orbital tooth triangular, short, directed dorsoanteriorly. No longitudinal ridge on ventral surface of external orbital angle. Epistome posterior margin with 3 triangular lobes, lateral lobes directed anteroventrally, median lobe directed ventrally. Antenna entering orbit through wide gap between inner orbital tooth and front. Mxp3 exopod with distinct flagellum. Chelipeds symmetrical in both male and female; markedly larger in male than in female. Chela palm upper surface with low ridge on proximal half extending from hinge with carpus, no row of granules; outer surface smooth, no granules or protuberance; inner surface without transverse crest; thick rim extending along occlusal margin of immovable finger to dactylar articulation on both outer and inner surfaces, thick rims of both outer and inner surfaces not interrupted near dactylar articulation. Upper-inner margin of movable finger without ornamentation. Ambulatory legs (P2–5) long, slender, dorso-ventrally flattened; distal anterior corner of each merus angled, followed proximally by low convexity; carpi and propodi not distinctly narrower than respective meri; dactyli as long as or longer than half length of respective propodi. Male thoracic sternum transversely wide; thoracic sternite 8 clearly exposed. Male pleon moderately wide, lateral margins of somites 3–5 straight; telson slightly exceeding proximal half of cheliped bases. G1 slender, long, reaching proximal half to distal end of thoracic sternite 5. Vulvae rounded, located on distal two-fifths of sternite 6, anterior margin adjacent to thoracic sternal suture 5/6, with rounded sternal vulval cover developed from lateral margin.

Etymology

The generic name ‘ Andamanium ’ is derived from an arbitrary combination of Andamans (type locality of the type species) and the suffix for the Labuanium ‘ -ium ’. Gender neuter.

Remarks

Andamanium gen. nov. is distinct in the family by the combination of the following characters: both the adult male chelipeds are enlarged, the outer surfaces of the chelae are smooth, and the fingers are long, strongly curved such that there is a large gape formed when they are closed ( Figure 27 (c)). In small males and females, however, the fingers are short and not prominently curved ( De Man 1908, pl. 11(6)). This male cheliped condition as well as the squarish carapace is superficially similar to species of Chiromantes s.s. (see Naruse and Ng 2008), but Andamanium differs markedly from Chiromantes s.s. in its symmetrical chelipeds (vs asymmetrical in Chiromantes s.s., with one chela enlarged and the other one normal) and the presence of epibranchial teeth on the lateral margin of the carapace (vs lateral margin entire in Chiromantes s.s.) (Ng and Liu 1999; Naruse and Ng 2008).

Figures

Figure 27. Mindanium cruciatum (Bürger, 1893), comb. nov. Holotype, SMF ZMG 623, female 16.3 × 16.6 mm (Mindanao, Philippines). a, habitus, dorsal view; b, right chela, outer view; c, right chela, upper view.