Oxypleurodon annulatum, Forges, Bertrand Richer De & Ng, Peter K. L., 2009

Forges, Bertrand Richer De & Ng, Peter K. L., 2009, New genera, new species and new records of Indo-West Pacific spider crabs (Crustacea: Brachyura: Epialtidae: Majoidea), Zootaxa 2025, pp. 1-20 : 5-6

Oxypleurodon annulatum n. sp.

Figs. 1 D–F, 3C, D

Material examined. Philippines. AURORA 2007: Stn. CP 2657, 16°00.41’N 121°54.37’E, 358–359 m, 20 May 2007: male holotype (11.1 x 6.5 mm, photographed) ( NMCR). – Stn. CP 2695, 14°45.28’N 123°38.36’E, 367–377 m, 26 May 2007: 2 ovigerous females (10.7 x 6.7 mm, photographed, 10.2 x 6.2 mm) ( NMCR). – Stn. CP 2696, 14°46.90’N 123°40.7’E, 363–367 m, 26 May 2007: 2 females (6.7 x 3.8 mm, 7.8 x 4.3 mm) ( ZRC 2009.0019). – Stn. CP 2727, 15°20.83’N 121°34.03’E, 318–353 m, 31 May 2007: 1 male paratype (14.5 x 9.2 mm) ( MNHN B31853). – Stn. CP 2731, 15°21.92’N 121°33.45’E, 353–376 m, 31 May 2007: 1 male (12.2 x 7.3 mm), 1 ovigerous female (11.5 x 7.1 mm) ( ZRC 2009.0020). – CP 2737, 16°01.88’N 121°52.53’E, 272 m, 1 June 2007: 1 male paratype (14.1 x 8.3 mm) ( MNHN B31854).

Diagnosis. Relatively small-size species (ovigerous female 10.2–11.5 mm carapace length). Carapace pyriform. Bifid rostrum with slightly diverging sharp spines, flattened, depressed on ventral side. Carapace covered by tomentum of thick setae, with white coloured circular, not prominently raised flattened plates: 2 semicircular supraocular plates slightly pointing at superior angle; round mesogastric plate with small granule dorsally, laterally with 2 large granules between branchial, gastric areas; large circular cardiac plate, finely punctulated; 2 small rounded branchial plates, forming sharp, laterally directed point; 2 postocular plates protecting eyes; large granule at upper part of subhepatic region; 3 white tubercles under subhepatic region;, row of 3 white tubercles under branchial region, posterior border of carapace outlined by thick ridge running from subranchial area; intestinal area forming rounded median plate. Buccal frame rectangular with operculifom maxillipeds. Antennae slightly longer than rostral spines. Chelipeds shorter than P2, surface smooth; merus triangular, slightly carinated; carpus short with 2 carinae on external side; propodus inflated, carinated on both borders; fingers curved, serrulated on inner border. Ambulatory legs thin, cylindrical; P2 longest. Anterior part of male thoracic sternal surface with 2 depressed areas. Ventral surfaces covered by tomentum of thick setae. G1 relatively straight, distal part dilated ( Fig. 3 C, D).

Etymology. From annulatum, Latin for “ringed” or “circular,” alluding to the several rounded plates that spot the carapace.

Remarks. Oxypleurodon annulatum n. sp. is similar to some other species of this genus having rounded plates like O. carbunculum ( Rathbun, 1906) , O. bidens ( Sakai, 1969) and especially O. mammatum (Guinot & Richer de Forges, 1986).

Oxypleurodon mammatum was described from north New Caledonia and later recorded from the Chesterfield Is. and Vanuatu (Richer de Forges & Ng in press). Its carapace has the same pattern of rounded plates as O. annulatum n. sp., but the two species can easily be separated by the carapace plates being prominently raised in O. mammatum , with a nipple-like tubercle at each peak (relatively flatter in O. annulatum n. sp., Fig. 1 D); the subhepatic region is inflated (relatively flatter in O. annulatum , Fig. 1 D); the presence of several large granules below the mesogastric plate (only a small granule in O. annulatum n. sp., Fig. 1 D); and the supraocular plate forming a sharp point anteriorly (gentle angle in O. annulatum n. sp., Fig. 1 D). Compared with O. bidens , described from Japan, O. annulatum n. sp. has a similar carapace shape, but is easily differentiated by the plates being more elongated and having a very characteristic branchial plate pointing anteriorly (see Fig. 1 D; Richer de Forges & Ng in press). The unusually rounded carapace of O. carbunculum (see below) easily distinguishes it from O. annulatum n. sp.

Figures

FIGURE 1. A – C, Oxypleurodon sanctaeclausi n. sp., holotype male (15.1 x 14.4 mm) (NMCR, ex ZRC 2008.0828); D – F, Oxypleurodon annulatum n. sp., holotype male (11.1 x 6.5 mm) (NMCR). A, D, overall dorsal views; B, E, lateral views of carapace; C, F, thoracic sternum and abdomen.

FIGURE 3. G 1 s. A, B, Oxypleurodon sanctaeclausi n. sp., holotype male (15.1 x 14.4 mm) (NMCR, ex ZRC 2008.0828); C, D. Oxypleurodon annulatum n. sp., holotype male (11.1 x 6.5 mm) (NMCR); E, F. Oxypleurodon carbunculum (Rathbun, 1906), male (19.9 x 14.4 mm) (BPBM Acc. N ° 1981.136). Scales = 0.5 mm.