Ethusina castro, Ahyong, 2008

Ahyong, Shane T., 2008, Deepwater crabs from seamounts and chemosynthetic habitats off eastern New Zealand (Crustacea: Decapoda: Brachyura), Zootaxa 1708 (1), pp. 1-72 : 26-29

Ethusina castro sp. nov.

( Figs 12A , 13A–B , 14A–E , 28A–B )

Type material. HOLOTYPE: NIWA 6067 , ovigerous female (cl 14.1 mm, cw 14.3 mm), Gisborne Knolls , 39°00.41–00.92’S, 179°17.83–18.48’E, 2672–2776 m, TAN0413/182, 17 Nov 2004.

Diagnosis. Carapace slightly broader than long; dorsal surface microscopically granular. Frontal median sinus broad, V-shaped; submedian teeth obtusely triangular, margins straight; lateral teeth narrow, acutely triangular, as long as submedian teeth. Orbital sinus shallow; outerorbital tooth small, conical, obtuse, not extending anteriorly beyond eye. Ocular peduncle oriented transversely, not extending laterally beyond outerorbital tooth. P2 and P3 long, slender, sparsely pubescent, otherwise smooth; meri 6.5 times as long as high or longer.

Description. Carapace subpyriform, slightly broader than long; dorsal surface microscopically granular, sparsely pubescent. Urogastric and cardiac regions slightly elevated, bordered by narrow grooves, deepest along lateral margins of metagastric region and posterior margins of protogastric region; cervical and branchial grooves shallow. Branchial regions inflated laterally. Front with broad, V-shaped median sinus; submedian teeth obtusely triangular, margins straight; lateral teeth narrow, acutely triangular, as long as submedian teeth. Orbital sinus shallow; outerorbital tooth small, conical, obtuse, not extending anteriorly beyond eye.

Ocular peduncle immobile, longer than cornea, oriented transversely; eyes partially visible dorsally, not extending laterally beyond outerorbital tooth.

Anterior margin of endostome below posterior margin of basal antennular segment. Antennular basal segment smooth, with blunt, rounded lobe anterior to articulation with segment 2.

Third maxilliped sparsely granular, lightly pubescent. Ischiobasis with broad, shallow submedian groove; ischium and basis demarcated by shallow groove. Merus about half ischium length, longer than broad. Propodus, carpus and dactylus unarmed, sparsely setose. Dactylus slightly compressed. Exopod reaching midlength of endopod merus.

Chelipeds equal in size and ornamentation; merus lightly pubescent, other segments smooth, glabrous, unarmed. Fingers straight, occlusal margins faintly sinuous; dactylus length 1.6 times dorsal margin of palm.

P2 and P3 long, slender, sparsely pubescent, otherwise smooth; dactyli broadly curved, with low longitu- dinal midrib, slightly shorter than combined length of respective propodi and carpi. P2 merus 6.5 times as long as high, when folded reaching slightly beyond apices of frontal teeth. P3 longest, merus as long as carapace, 7.2 times as long as high.

P4 and P5 sparsely pubescent; longer than merus of P3; dactyli about half as long as propodi, with corneous apex and 5–7 obliquely inclined, spines on ventral margin. P5 merus, when folded against carapace, reaching anterior quarter of carapace.

Female abdomen sparsely pubescent, smooth; widest at somite 3; telson subtriangular, wider than long, margins straight, apex rounded. Egg diameter 0.5 mm.

Etymology. Named for fellow carcinologist, Peter Castro, for his contributions to the knowledge of Brachyura, especially Dorippidae ; used a noun in apposition.

Remarks. Ethusina castro sp. nov. closely resembles E. challengeri ( Miers, 1886) (type locality: Japan) and differs from other congeners in sharing the short, blunt outerorbital tooth, low, blunt submedian frontal teeth of the carapace, small, narrow cornea, and swollen, pyriform, relatively smooth carapace (only sparsely and microscopically granular) that is wider than long ( Fig. 12A , 14A–B ). The new species differs from E. challengeri in the angular rather than rounded sinus separating the submedian and lateral frontal teeth, angular rather rounded apices of the submedian frontal teeth, in the laterally rather than anterolaterally directed eyes, which do not extend beyond the outerorbital teeth, and in lacking a spine on the basal antennular segment anterior to the articulation with the second segment. Spiridonov & Türkay (2007) reported E. challengeri from the Arabian Sea, noting that their females differed from the female holotype in having the lateral frontal teeth as wide as the submedian teeth (median teeth of Spiridonov & Türkay 2007) rather than markedly narrower. Though not discussed by Spiridonov & Türkay (2007), comparison of their figure 9a–b (female holotype of E. challengeri ) with their figure 9c (Arabian Sea female) also appears to show the P2 merus of the holotype as considerably longer than that of the Arabian Sea female (distinctly overreaching rather than falling short of the carapace front). Moreover, the apex of the male G1 as figured by Spiridonov & Türkay (2007: fig. 10a) and Castro (2006: fig. 16c) appears to differ in shape, being bluntly angular versus rounded, respectively. The Arabian Sea specimens attributed to Ethusina challengeri by Spiridonov & Türkay (2007) should be re-examined; they could be referable to an undescribed species.

Ethusina castro also resembles E. abyssicola ( Smith, 1884) and E. alba ( Filhol, 1884) from the western and eastern Atlantic, respectively, in the short outer orbital teeth and arrangement of frontal carapace teeth. The submedian frontal teeth of E. abyssicola , however, are prominent and acute, rather than low and obtuse in E. castro . Ethusina alba is readily distinguished from E. castro by carapace proportions and surface ornamentation, being longer than wide rather than wider than long, and the coarsely rather than microscopically granular carapace surface.

Unfortunately, E. castro is known only from the ovigerous female holotype, so comparisons of gonopod morphology must await collection of males.

Distribution. Presently known only from Gisborne Knolls, northeastern New Zealand; 2672–2776 m.

Figures

FIGURE 12. A, Ethusina castro sp. nov., ovigerous female holotype, cl 14.1 mm, cw 14.3 mm (NIWA 6067). B, Ethusina rowdeni sp. nov., male holotype, cl 9.6 mm, cw 9.3 mm (NIWA 6078).

FIGURE 13. A–B Ethusina castro sp. nov., ovigerous female holotype, cl 14.1 mm, cw 14.3 mm (NIWA 6067). C–D Ethusina rowdeni sp. nov., male holotype, cl 9.6 mm, cw 9.3 mm (NIWA 6078). A, C, anterior. B, D, ventral.

FIGURE 14. A–E, Ethusina castro sp. nov., ovigerous female holotype, cl 14.1 mm, cw 14.3 mm (NIWA 6067). F–L, Ethusina rowdeni sp. nov., male holotype, cl 9.6 mm, cw 9.3 mm (NIWA 6078). A, F, anterior carapace, dorsal view, dorsal. B, G, anterior carapace, ventral view. C, H, right third maxilliped. D, J, right P5 dactylus and propodus. E, I, abdomen. K, right G1, abdominal view. L, right G2, sternal view. Scale: A–B = 2.0 mm, D, J = 0.5 mm, E = 0.7 mm, C, F–G = 1.6 mm, I–H = 1.3 mm, L–K = 0.8 mm.

FIGURE 28. A–B, Ethusina castro sp. nov., ovigerous female holotype, cl 14.1 mm (NIWA 6067), dorsal and ventral views. C, Trichopeltarion fantasticum Richardson & Dell, 1964, female, cl 53.1 mm (NIWA 6754). D, Trichopeltarion janetae sp. nov., male, cl 27.9 mm (NIWA 29650). E, Chaceon yaldwyni Manning, Dawson & Webber, 1990, 1 male, cl 55.2 mm (NIWA 6716). F, Lyreidus tridentatus De Haan, 1841, male, cl 38.5 mm (NIWA 6720). Photo credits: R. Stewart (A–C, E–F), C. Marriot (D).