Rochinia ahyongi, Published, 2009

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 : 30-33

Rochinia ahyongi sp. nov.

( Figs 12a, b, 13a–g)

? Sphenocarcinus . — Clark & O’Shea 2001: 15

Material Examined. Rumble V Seamount: NIWA stn Z10806 , 1 male, 8.7 mm x 11.7 mm (incl. spines and rostrum), 36°08.84–08.59’S, 178°12.24–11.99’E, 951– 772 m, Tangaroa , stn TAN0107/225, 23 May 2001 ( NIWA 42391 .

Holotype. Male, 8.7 mm x 11.7 mm, NIWA stn Z10806 , 36°08.84–08.59’S, 178°12.24–11.99’E, 951– 772 m, Tangaroa , stn TAN0107/225, 23 May 2001 ( NIWA 42391 ).

Etymology. The specific name of the new species acknowledges the valuable contribution of Shane Ahyong (NIWA) to our knowledge of New Zealand Brachyura, especially deep-sea species.

Description. Carapace pyriform, much longer than wide, surface convex, finely granular with sparse, scattered, long, fine, straight or hooked setae. Rostral spines long (making up approximately 32% of total length), strongly divergent (distance between tips 2.4 basal width), 2 pairs of lateral spines, shorter anterior pair at mid-point of carapace (making up 30% of width), longer posterior pair further back (making up approximately 38% of width), all spines narrowing to blunt tip, cardiac region with low swelling in mid-line. Posterior carapace margin with rounded protuberance. Orbit incomplete dorsally, and ventrally, with small preorbital tubercle, postorbital corner slightly produced, blunt, remainder of orbital margin unarmed.

Basal article of antenna fixed, lateral margin straight, anterolateral corner slightly produced, articles 2, 3 successively shorter, flagella not reaching tip of rostral spine. Basal article separated from post-orbital lobe by narrow U-shaped hiatus.

Chelipeds (P1) same length as CW (including spines), narrow, palm about 5 times as long as wide, fingers elongate margins approximated; cutting edges with 3, 4 very small teeth on both chelipeds. Moveable finger approximately 0.5 propodus length. Walking legs (P2–P5) narrow, smooth, first pair longest 1.25x carapace length (decreasing in length posteriorly), merus about same length as carpus + propodus length, margins unarmed; dactylus about same length as propodus.

Abdomen of 6 free somites, second somite widest decreasing in width posteriorly, penultimate somite much wider than long, telson as wide as long, posterior margin rounded. First male gonopod (G1) straight, flattened, tip bilobed, medial lobe angled and longer.

Remarks. One other species of this genus is known from the vicinity of the Kermadec Is, Rochinia riversandersoni ( Alcock, 1895) , but the two species are easily distinguished by the fact that this species has 12 long carapace spines while R. ahyongi sp. nov. only has four spines. Both species do have long divergent rostral spines. In the Australasian area the only spider crab resembling R. ahyongi sp. nov. is Rochinia fultoni ( Grant, 1906) from New South Wales and Tasmania, but it has anterior lateral spines that are short and triangular (longer and spine-like in R. ahyongi sp. nov.), a medial cardiac tubercle (only a low swelling) and a short spine on the posterior margin (only a rounded protuberance). See also Poore et al. (2008) who have a photo of R. fultoni . The male gonopod of R. ahyongi sp. nov. is similar to that of other Rochinia species many of which terminate bluntly (see Griffin & Tranter, 1986a, figs 62–64), but in the new species it is bilobed, as seen in R. brevirostris (Doflein, 1904) for example.

Even after the revisions by Griffin & Tranter (1986a) and Tavares (1991), the genus Rochinia includes a very diverse range of some 30 species from tropical and temperate oceans worldwide, all living in deepwater> 650 m. Relevant to the two New Zealand species, one of the main features that separate all the species of the genus is the number and length of carapace spines. At one extreme we have species like R. histrix ( Stimpson, 1871) with more than a dozen long spines and at the other R. moluccensis Griffin & Tranter, 1986 with only one pair of short lateral spines. The two species now known from New Zealand seas, R. riversandersoni and R. ahyongi sp. nov., lie near opposite ends of this spectrum and perhaps after some future revision they could end up in different genera. Carapace spines are no doubt a defence against predators, but some species of Rochinia also carry symbiotic anemones, placed on their carapace. Despite being very spiny, the holotype of Rochinia griffini was carrying an anemone that almost totally covered its back ( Davie & Short, 1989). One might suspect that it would have been difficult for the anemone to adhere to its host because of the spines.

Distribution this is a New Zealand endemic crab known only from the Rumble V Seamount. Depth range is 951– 772 m.