Ethusina insolita, Ng & Ho, 2003

Ng, Peter K. L. & Ho, P. - H., 2003, On The Deep-Water Dorippid Crabs Of The Genus Ethusina Smith, 1884 (Crustacea: Decapoda: Brachyura) From Taiwan, Raffles Bulletin of Zoology 51 (1), pp. 71-85 : 81

Ethusina insolita , new species

( Figs. 12 , 13 )

Material examined. – Holotype – male, 8.8 by 10.4 mm ( NTOU), Station CP 53, 24 15.7’N, 122 11.6’E, 2947- 2903 m, coll. TAIWAN 2000, R. V. “Fishery Researcher 1”, 3 Aug.2000.

Diagnosis. – Carapace longer than broad; dorsal surface gently convex, with scattered low granules visible without magnification, regions not well defined. Front projecting anteriorly, with 4 teeth; median teeth low, rounded, lobiform, separated by shallow, broad concavity; lateral teeth low, directed obliquely outwards, separated from median teeth by shallow concavity. External orbital spine relatively short, triangular, directed anteriorly or almost so, tip not reaching bases of median frontal teeth. Lateral carapace margins gently sinuous, with posterior part convex. Posterior carapace margin gently concave. Chelipeds subequal; fingers slightly longer than palm; cutting edges with low teeth. P2 and P3 smooth, glabrous; P3 longest, merus 9.6 times as long as wide, propodus 7.7 times as long as wide; dactylus very elongate. Male abdomen with segments 3-5 completely fused, only traces of median sutures visible, segment 5 with prominent tranverse ridge; segment 6 rectangular, broader than long, lateral margins convex; telson triangular, lateral margins almost straight. G1 stout, distal part subtruncate.

Etymology. – The name is derived from the Latin for uncertain, alluding to the systematic status of the species.

Remarks. – This new species is rather problematic even though it is represented by a good male specimen. With regards to its carapace form and pereiopodal proportions, it is remarkably close to E. dilobotus Chen, 1993 . Nevertheless, the external orbital spine of E. insolita , new species, is directed distinctly anteriorly rather than slightly obliquely, the male telson is relatively more elongate, and the G1 is relatively shorter and stouter. These differences by themselves can be regarded as variation, especially since E. dilobotus is known only from the type specimen from New Caledonia. The male abdominal segment five of E. insolita , however, has a prominent transverse ridge that spans much of its width, a feature that is absent on E. dilobotus (cf. Chen, 1993: fig. 19c). This character, together with the other differences observed earlier, strongly suggest that we are dealing with a different species here.

Figures

Fig. 12. Ethusina insolita, new species. Holotype male, 8.8 by 10.4 mm (NTOU). A, overall view; B, carapace.

Fig. 13. Ethusina insolita, new species. Holotype male, 8.8 by 10.4 mm (NTOU). A, carapace; B, left orbit, antenna and antennule; C, right P2; D, right P5; E, left chela and carpus; F, male abdominal segments 3-6 and telson (3-5 fused); G, H, left G1 (setae denuded); I, left G2. Scales: A, C = 5.0 mm; B = 2.0 mm; D-I = 1.0 mm.