Dicranodromia delli Ahyong, 2008

Published, First, 2009, New records of crabs (Decapoda: Brachyura) from the New Zealand region, including a new species of Rochinia A. Milne-Edwards, 1875 (Majidae), and a revision of the genus Dromia Weber, 1795 (Dromiidae), Zootaxa 2111, pp. 1-66 : 8-11

Dicranodromia delli Ahyong, 2008

( Fig. 1b)

Dicranodromia delli Ahyong, 2008: 7 , figs 2–4.

Material Examined. East of Coromandel Peninsula: NIWA stn Z9840, 1 male, 9.0 mm x 13.0 mm, 36°30.27’S, 176°30.45’E, 990–1100 m, Kaharoa, stn KAH9901/53, 05 June 1999 ( NIWA 48726 ) .

Gothic Seamount (Graveyard Complex), Chatham Rise: NIWA stn Z19714, 1 male, 6.5 mm x 9.2 mm, 42°43.95’S, 179°53.91’W, 1076– 990 m, Tangaroa , stn TAN0104/153, 18 Apr. 2001 ( NIWA 48727 ) .

Description of male. P1 similar to female (see Ahyong 2008, p7), sparse conical granules, spinules especially dorsally, ventrally; fingers slightly shorter than dorsal margin of propodus, occlusal margins armed with 5 or 6 almost obsolete teeth, only distal 2 teeth demarcated, inter-locked; fingers with narrow gape proximally when closed. P3 longest (2.2CL); P2, P3 dactyli with 12–15 well developed corneous spines along inner margins. P4 dactylus short curved opposed by 3 longer corneous spines with 1or 2 spines on outer propodal margin, inner margin of dactylus armed with 3 or 4 small spines. P5 dactylus, short, curved, opposed by 3 corneous spines with 4 spines on outer propodal margin, small corneous spine on outer margin of dactylus.

Gonopods as for all species of the Homolodromiidae ( Guinot 1995: 177, figs.4A–C): G1 stout, straight, spiralling to densely setose apex containing aperture into which needle-like G2 fits. G2 longer than G1. Telson triangular, posterior margin sub-acute, 1.4 as long as wide, fused with somites 5 and, 6] so that no flexibility allowed, but all sutures evident. No abdominal locking mechanism, but abdomen is folded ventrally at joint of somites 4 and 5 where limited flexibility eliminates need for abdominal retention against sternum. No vestigial pleopods on somites 3 – 5. Uropods ventral, reduced (length 0.12 telson width), oblong, calcified, rigid.

Remarks. Only a female (15.5 mm x 19.0 mm) from the Nukuhou Seamount, Bay of Plenty, was available when Ahyong (2008) described D. delli . Two males are reported here from off the Coromandel Peninsula and Chatham Rise, both much smaller than the type. The known depth range is now 990–1134 m, slightly deeper than D. spinulata . Guinot (1995) provided a key to the identification of the 16 Atlantic and Indo-West Pacific species of Dicranodromia then known. Ng & McLay (2005) described a new species, D. danielae Ng & McLay, 2005 , from the Philippines and the new species, D. delli , make a total of 18 species.

The two New Zealand species, D. delli from D. spinulata , can be distinguished from each other by the density of spinules on the carapace, but the best way to separate them is by comparing the proportions of the P2 and P3 articles ( Fig. 1a, b): for female D. delli merus length is around six times the merus height and propodus length is around 10 times its height (eight and nine times respectively in males) and twice the length of the dactylus (2.2 times and 2.4 times respectively in males). In D. spinulata the P2 and P3 meri length is around 5 times height, propodus length less than 7 times height and propodi are only 1.6 times dactylus length. In D. delli the P2 and P3 are therefore longer and more slender. The reduced camouflage-carrying P4 and P5 are also longer than in D. spinulata . An additional difference between the two species is that the inner margins of the P2 and P3 dactyli of D. delli are armed with 12–15 corneous spines whereas in D. spinulata there are only seven or eight. Ahyong (2008) also reported Homolodromia kai Guinot, 1993 from the Bay of Plenty at a depth of 632– 458 m. This species is easily distinguished from the two species of Dicranodromia by a longer pair of walking legs than Dicranodromia and by the last pair of prehensile legs having a distal prolongation on the propodus, which is similar to the fixed finger of the chelipeds.

There are several secondary sexual characters between male and female D. delli as follows: suture between last abdominal somite and telson is faint or absent in females (clearly evident in males); P3 of females is 1.9CL (2.2CL in males); P 4 in females has two corneous spines on outer margin and three or four opposing spines (males have one or two corneous spines on outer margin and 3 opposing); no corneous spines on the inner margin of dactylus were reported by Ahyong (2008) (inner margin of male dactylus is armed with 3 or 4 inclined small spines). The female P5 has two corneous spines on the outer margin and 7 spines opposing the dactylus ( Ahyong 2008) (male has a spine on the outer propodal margin and three opposing spines); female has 3 or 4 obliquely inclined spines on the inner margin of the dactylus (male has a spine on the outer propodal margin and 3 spines opposing); no spines on outer margin of the P5 dactylus (one small spine in male).

The number and arrangement of spines on the P4 and P5 propodi and dactyli for D. delli and D. spinulata is summarized in Table 2. There is considerable variation in these spines both within and between species. Some of this variation is caused by spines being broken off so it is probably best to take the larger number for each category as being representative of the species. Guinot (1995) provides detailed information for several species and the present two species fall within this range. Homolodromiids have comparatively large numbers of spines on their reduced last two pairs of pereopods and these are used for hold pieces of camouflage that are carried above the crab. Such large numbers of corneous spines are also found in the primitive Dromiidae such as in the species of Sphaerodromia Alcock, 1899 . Large numbers of corneous spines on camouflage-carrying pereopods is a plesiomorphic character state.

The two homolodromiid genera differ in Homolodromia the propodal spines are on an extension of the propodus with resulting longer dactyli, whereas in Dicranodromia the ventral distal margin of the propodus is not extended so that the dactylus is shorter and more strongly curved. Species of both genera can have spines on the inner margin of the dactyli as well as distal propodal spines surrounding the base of the dactyli.

In several species of both Dicranodromia and Homolodromia , males have vestigial pleopods on somites 3, 5, in addition to the gonopods of somites 1, 2 ( Guinot, 1995, 179). D. delli males do not have any vestigial pleopods other than the uropods and in this respect they are the same as the D. spinulata males listed above. No evidence of the “rudiments” mentioned in the description of D. spinulata by Guinot (1995, 225) could not be found in the New Zealand specimens. The uropod length in male D. spinulata (0.13 telson width) is also similar to those in male D. delli .

Distribution. Dicranodromia delli is a New Zealand endemic originally reported from the Nukuhou Seamount, Bay of Plenty, but now known from East of Coromandel and the Gothic Seamount (Graveyard Complex), Chatham Rise Peninsula. Depth range is 990–1134m.