Dicranodromia delli, 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 : 7-10

Dicranodromia delli sp. nov.

( Figs 2–4 )

Type material. HOLOTYPE: NIWA 18049 , ovigerous female (cl 19.0 mm, cw 15.5 mm), Nukuhou Seamount, 37°14.22–14.52’S, 177°16.64’E, 1126–1134 m, TAN0413/54, 11 Nov 2004.

Diagnosis. Carapace ovate, longer than broad, strongly convex transversely and longitudinally; dorsal surface covered with short, stiff setae and fine spinules, becoming elongate granules on central surface; frontal lobes with inner and outer margins concave; margin near orbit with several spinules. Outer orbital tooth a slender, anterolaterally directed spine, inner margin with several spinules. Epistome with posterior surface unarmed. Cheliped propodi with well-spaced conical granules or spinules. P2–3 long, slender, meri and carpi with scattered elongate granules or spinules, propodi smooth; meri exceeding 6 times height; propodi exceeding 10 times height; dactyli half propodus length.

Description. Carapace ovate, longer than broad, prominently convex transversely and longitudinally; regions faintly indicated; dorsal surface covered with short, stiff setae and fine spinules, becoming elongate granules on central surface; front with 2 prominent triangular lobes separated by deep U-shaped sinus, inner and outer margins concave, distally rounded; margin near orbit with several spinules. Outer orbital tooth a slender anterolaterally directed spine, inner margin with several spinules. Anterolateral and posterolateral margins rounded, spinulose. Posterior margin faintly concave. Suborbital, pterygostomial and sub-branchial regions, spinulate. Epistome with anterior and median surfaces sparsely granular or spinulate; posterior surface unarmed. Basal antennal and proximal antennular segments covered with small spinules or granules.

Third maxilliped ischiobasis demarcated by distinct groove; ischium quadrate, surface smooth, margins with short teeth or granules. Merus subovate, as long as ischiobasis; 1.6 times longer than wide; surface sparsely spinulate, margins spinulate. Propodus, carpus and dactylus unarmed. Exopod surface smooth, inner mesial and outer proximal margins spinulate; apex reaching slightly beyond midlength of merus of endopod.

Chelipeds equal in size and ornamentation, covered with short, stiff, scattered setae. Merus surfaces with well-spaced conical granules or spinules, most pronounced dorsally and ventrally. Carpus with pair of outer distal spines and small, scattered conical granules or spinules. Propodus relatively slender, not swollen; surfaces with well-spaced conical granules or spinules. Fingers slightly shorter than dorsal margin of palm; glabrous, smooth, forming narrow gape when closed; occlusal margin of pollex slightly crenulate, that of dactylus evenly curved.

P2–3 long, slender, setose; meri and carpi with scattered elongate granules or spinules; propodi smooth; dactyli stongly curved, ventral margin lined with corneous spines, apex corneous. P2 merus 6.6 times as long as high; propodus 10.6 times as long as high; dactylus half propodus length. P3 longest, 1.9 times carapace length; merus 6.6 times height; propodus 11.1 times height; dactylus half propodus length.

P4–5 setose, smooth except for few scattered spinules on merus; distal margin of P4 propodus with 2 dorsal and 3 or 4 movable ventral spines opposing dactylus; distal margin of P5 propodus with 2 dorsal and 7 movable ventral spines opposing dactylus. P4–5 dactyli markedly shorter than respective propodi, stongly curved, each with corneous apex and 3 or 4 obliquely inclined, corneous spines on ventral margin. P5 merus, when folded against carapace, reaching lateral extent of cervical groove.

Mature female abdomen subovate, forming brood chamber; telson triangular, fused with somites 5 and 6; somites 5 and 6 demarcated by distinct suture; demarcation between somite 6 and telson faint or absent.

Etymology. Named for the late Richard. K. Dell, in recognition of his substantial contributions to New Zealand carcinology.

Remarks. Dicranodromia delli sp. nov. is the eleventh Indo-West Pacific species of the genus to be recognised (for full species list see Guinot 1995; Ng & McLay 2005; Ng & Naruse 2007) and the first species of Homolodromiidae to be described from New Zealand. Dicranodromia delli most closely resembles D. spinu- lata Guinot, 1995 (from New Caledonia and now New Zealand) and D. pequegnati Guinot, 1995 (from off West Africa) in sharing the finely spinulate carapace surface, sparse dorsal setation, and slender, spinulate outerorbital teeth. The new species differs from D. spinulata and D. pequegnati in having the spinulation of the central surface of the carapace reduced to short or low granules rather than distinct spinules, sparse rather than dense setation on the pereopods and the more slender P2 and P3 as measured by segment proportions (compare Figs 1C & 2–3 ). In D. delli , the P2 and P3 merus length is 6.6 times height, the propodus length exceeds 10 times its height and is twice the length of the dactylus. In D. spinulata and D. pequegnati , the P2 and P3 meral length is less than 5 times height, the propodus length is less than 7 times the height and the dactyli are about 0.6 propodus length. Dicranodromia delli further differs from D. spinulata in having a smooth rather than spinulose posterior surface of the epistome ( Fig. 4B ), and distinctly concave rather than almost straight lateral frontal margins ( Fig. 4A–B ). In addition, D. delli apparently attains a much larger size (cl 19.0 mm versus 11.0 mm), being almost twice the maximum known lengths of D. spinulata and D. pequegnati .

The holotype is a gravid female, carrying 18 large, late stage embryos and ‘megalopae’ (3.2–3.5 mm) similar to those reported by Guinot (1995) for D. nagaii Guinot, 1995 .

Distribution. Presently known only from Nukuhou Seamount, Bay of Plenty, northeastern New Zealand; 1126–1134 m.

Figures

FIGURE 1. A, Dagnaudus petterdi (Grant, 1905), female, pcl 44.1 mm (NIWA 34784). B, Homolodromia kai Guinot, 1995, female, cl 19.9 mm, cw 14.6 mm (NIWA 6761). C, Dicranodromia spinulata Guinot, 1995, male, cl 9.6 mm, cw 6.8 mm (NIWA 34933). D, Cymonomus clarki sp. nov., ovigerous female holotype, cl 6.9 mm, cw 6.6 mm (NIWA 29666). E, Lyreidus tridentatus De Haan, 1841, female, cl 46.6 mm (NIWA 6723). F, Cymonomus aequilonius Dell, 1971, female, cl 7.7 mm, cw 6.7 mm (NIWA 34966).

FIGURE 2. Dicranodromia delli sp. nov., ovigerous female holotype, cl 19.0 mm, cw 15.5 mm (NIWA 18049). A, dorsal habitus. B, carapace, dorsal view.

FIGURE 3. Dicranodromia delli sp. nov., ovigerous female holotype, cl 19.0 mm, cw 15.5 mm (NIWA 18049). A, right lateral. B, anterior. C, ventral. D, right pereopods.

FIGURE 4. Dicranodromia delli sp. nov., ovigerous female holotype, cl 19.0 mm, cw 15.5 mm (NIWA 18049). A, anterior, dorsal view. B, anterior, ventral view. C, left third maxilliped. D, left P5 dactylus and propodus. Scale: A–C = 2.0 mm, D = 1.0 mm.