Ethusina rowdeni, 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 : 29-31

Ethusina rowdeni sp. nov.

( Figs 12B , 13C–D , 14F–L )

Type material. HOLOTYPE: NIWA 6078 , male (cl 9.6 mm, cw 9.3 mm), Whakatane Seamount, 36°47.26– 47.45’S, 177°28.17–28.12’E, 1292–1336 m, TAN0413/10, 8 Nov 2004.

Diagnosis. Carapace slightly broader than long; dorsal surface finely and densely granular. Median frontal sinus broad, V-shaped, wider than orbital and lateral frontal sinuses; submedian teeth obtusely triangular, apex sharp, mesial margins faintly convex, lateral margins slightly concave; lateral teeth, reaching anteriorly as far as apices of submedian teeth. Orbital sinus deep, V-shaped. Outerorbital tooth a slender spine, extending anteriorly to base of frontal median sinus. Eyes not extending laterally beyond outer orbital tooth. P2 and P3 long, slender, finely granular; meri exceeding 8.5 times as long as high. G1 apex rounded, aperture broad, elongate, almost half-length of narrow distal portion, slightly flared laterally. G2 apex sharp, pointed, inclined anterolaterally.

Description. Carapace slightly broader than long; dorsal surface finely and densely granular, sparsely setose. Mesogastric, urogastric, cardiac regions slightly elevated, urogastric region bordered by conspicuous lateral grooves; cervical groove shallow and partially visible; branchial grooves shallow but conspicuous. Branchial regions inflated laterally.

Front with broad, V-shaped median sinus, wider than orbital and lateral frontal sinuses; submedian teeth obtusely triangular, apex sharp, mesial margins faintly convex, lateral margins slightly concave; lateral teeth narrow, acute spines, reaching anteriorly as far as apices of submedian teeth. Orbital sinus deep, V-shaped, asymmetrical, mesial margins almost straight, lateral margins concave. Outer orbital tooth a slender spine, extending anteriorly to base of frontal median sinus.

Ocular peduncle immobile, longer than cornea, directed laterally. Eyes partially visible dorsally, not extending laterally beyond outerorbital tooth.

Anterior margin of endostome below posterior margin of basal antennular segment. Antennular basal segment sparsely granular, with short tooth anterior to articulation with segment 2.

Third maxilliped finely and densely granular, sparsely setose. 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 and carpus finely granular, sparsely setose, other segments smooth, glabrous, unarmed. Palm slightly inflated. Fingers straight, occlusal margins faintly sinuous; dactylus length 1.1 times dorsal margin of palm.

P2 and P3 long, slender, finely granular, sparsely and finely setose; dactyli broadly curved, smooth, with longitudinal midrib, slightly shorter than combined length of respective propodi and carpi. P2 merus 8.8 times as long as high, when folded reaching beyond apices of frontal teeth by about 0.2 merus length. P3 longest, merus as long as carapace, 9.3 times as long as high.

P4 and P5 finely and sparsely setose; slightly longer than merus of P3; dactyli about as long as propodus, with corneous apex and 6 or 7 obliquely inclined spines on ventral margin. P5 merus, when folded against carapace, reaching anterior quarter of carapace.

Male abdomen sparsely and finely granular, finely and sparsely setose; fused somites 3–5 with proximal third more swollen than anterior; somite 6 subrectangular, half as long as wide; telson triangular, 1.4 times wider than long. G1 straight; distal 0.4 narrow, apex rounded; distomesial margin with short spines along tip; aperture broad, elongate, almost half-length of narrow distal portion, slightly flared laterally. G2 as long as G1; proximal segment straight, about 0.4 times total length of G2; distal portion flattened, with proximal bend, apex sharp, pointed, inclined anterolaterally.

Etymology. Named in hounour of Ashley Rowden, for his contributions to the knowledge of New Zealand seamounts.

Remarks. Ethusina rowdeni sp. nov. is the second dorippid to be recorded from New Zealand. It closely resembles E. huilianae Castro, 2005 ( French Polynesia) in lacking the orbital fissure, short ocular peduncles, four frontal spines, long, slender outer-orbital spines and long, slender P2 and P3 meri in which the former, when folded, extends anteriorly well beyond the frontal teeth. The new species differs from E. huilianae in the following features: the base of the median frontal sinus is at a similar level to that of the lateral frontal sinuses, rather than being considerably deeper; the median frontal sinus is wider than both the lateral and orbital sinuses, rather than being subequal to, and narrower, respectively; the inner margins of the lateral frontal sinuses are relatively straight, rather than strongly sinuous with a pronounced, proximal step ( Fig. 14F ); the P2 merus is more slender (length: height ratio 8.8 versus 7.5–8.2) ( Fig. 12B ); the G1 has a large and elongate, rather than small ovate aperture ( Fig. 14K ); the G1 apex is inclined laterally rather than mesially ( Fig. 14L ).

The two New Zealand species of Ethusina are readily distinguished by the length of the outerorbital tooth or spine: a small tubercle in E. castro versus a long spine in E. rowdeni .

Distribution. Whakatane Seamount, eastern New Zealand; 636–1336 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.