Rhadinoplax microphthalmus (Guinot & Richer de Forges, 1981)

Castro, Peter & Ng, Peter K. L., 2008, Rhadinoplax, a new genus of Progeryonidae Števčić, 2005, for Carcinoplax microphthalmus Guinot & Richer de Forges, 1981, and a redescription of Paragalene longicrura (Nardo, 1868) (Crustacea: Decapoda: Brachyura: Goneplacoidea), Zootaxa 1777, pp. 53-68 : 57-62

Rhadinoplax microphthalmus (Guinot & Richer de Forges, 1981)

( Figs. 1–5)

Carcinoplax microphthalmus Guinot & Richer de Forges 1981a: 1113, 1115 , pl. 6, figs 1, 1a, 2, 3 (nomen nudum); Guinot & Richer de Forges 1981b: 245, figs. 9 C, D, 10 E–H [ New Caledonia]; Guinot 1989: 288 [discussion], figs. 1, 15, pl. 8, fig. I [Philippine Is.]; Castro 2007: 623, 625; Ng et al. 2008: 84.

Carcinoplax microphthalma — Matsuzawa 1993: 21, fig. 2 (colour) [ Japan].

Type material of Carcinoplax microphthalmus Guinot & Richer de Forges, 1981 : ♂ holotype, 53.3 x 61.4 mm, Tombo Reef , New Caledonia, trap facing shipwreck, 400 m, 06.06.1979 ( MNHN-B 6832 ) ; ♂ paratype, 53.4 x 60.0 mm, ♀ paratype, 38.9 x 43.0 mm, Hienghen Pass , trap on hard bottom, New Caledonia, 400 m ( MNHN-B 6830 ) ; ♂ paratype, 53.2 x 61.8 mm, Koumac Pass , trap on muddy bottom, New Caledonia, 400 m ( MNHN-B 6828 ) ; ♂ paratype, 40.2 x 44.7 mm, Boulari Pass , trap, New Caledonia, 400 m ( MNHN-B 6829 ) ; 2 ♂♂ paratypes, 37.5 x 41.7 mm, 33.1 x 37.0 mm, Belade Pass , trap, New Caledonia, 400 m ( MNHN-B 6831 ) , ♀ paratype, 42.3 x 46.7 mm, Gazelle Pass , trap, New Caledonia, 400 m ( MNHN-B 6833 ) .

Material examined. Philippine Islands. Bohol. Balicasag I., off Panglao I., tangle nets of local fishermen, P. Ng coll., 01.2004 : 1 ♂, 1 ♀ ( MNHN-B 29735 ) , 2 ♀♀, 49.6 x 54.0 mm, 42.4 x 46.7 mm ( ZRC 2008.001 ) ; 01.2004: 1 ♂, 42.1 x 45.7 mm ( ZRC 2008.002 ) ; 29.05.2004: 2 ♀♀, 40.5 x 45.8 mm, 45.0 x 50.2 mm ( ZRC 2008.003 ) ; 50–500 m, 28.11.2001: 1 ♂, 53.5 x 58.2 mm, 1 ♀ 48.4 x 54.0 mm ( ZRC 2001.0530 ) ; 02.2004: 1 ♂, 59.7 x 67.5 mm ( ZRC 2008.004 ) ; 50–500 m, 03.2004: 1 ♀ ( ZRC 2004.0709 ) .— Panglao I., Maribohoc Bay , tangle nets, 100–300 m, T. J. Arbasto coll., 11.2003 –04.2004 : 1 ♂, 41.0 x 46.4 mm ( ZRC 2008.005 ) .

Indonesia. Tanimbar Islands . KARUBAR: stn CP 79, 09º16’S, 131º22’E, 250– 239 m, 03.11.1991: 1 ♂ ( MNHN-B 29374 ), 3 pre-adult ♀♀ ( MNHN-B 30547 ) .

New Caledonia. Tombo Reef , trap facing shipwreck, 400 m, 06.06.1979: ♂ holotype ( MNHN-B 6832 ) . Trap, N.O. Dawa , 22º30.96’S, 166º26.24’E, 312 m, 17.11.1993: 1♀ ( MNHN-B 29375 ) . BATHUS 4: stn CP 900, 20º16.74’S, 163º50.06’E, 580 m, 03.08.1994: 1 ♂ ( MNHN-B 29376 ) .

Description. Carapace suboctagonal ( Figs. 1, 2A, B; also see Guinot & Richer de Forges 1981b: pl. 6, figs. 1–3, as Carcinoplax microphthalmus ; Guinot 1989: pl. 8, fig. I, as C. microphthalmus ); front lamellar, marked by slight median notch, 2 weak lateral lobes on each side; notch between front, supraorbital border. Orbits narrow, not expanded on outer portion; supraorbital borders short, slightly curved, with 2 shallow notches. Anterolateral borders curved; posterolateral borders long, arched ( Figs. 1, 2A, B). Dorsal surface of carapace granular, strongly convex, without clear indication of regions ( Figs. 1, 2A, B) except 2 shallow, curved or straight grooves on cardiac region. Outer orbital angle with short, triangular tooth; 2 anterolateral teeth on each side of carapace strongly reduced or absent in largest specimens ( Figs. 1, 2A, B). Basal antennal articles short, mobile, almost closed by extension of carapace margin, thus distalmost (third) article almost reaches front ( Fig. 2C–F). Eye peduncles short, cornea spherical, small, only slightly expanded distally ( Fig. 2C–F). Suborbital border with blunt inner tooth. Anterior border of endostome well demarcated from buccal cavern, ridges faint but clearly defined. Third maxillipeds completely close buccal cavern; anterior outer margin expanded, rounded. Endostomial ridge distinct. No visible stridulating mechanism.

Cheliped (P1) fingers slender, equal to or less than half propodus length, tips darker coloured ( Figs. 1, 2A, B; also see Guinot & Richer de Forges 1981b: pl. 6, fig. 1a, as C. microphthalmus ). Carpus with acute tooth on inner margin ( Figs. 1, 2A, B). P2–P5 meri, carpi, propodi slender; dorsal margins unarmed; dactyli slender, setose (more prominent in smaller specimens) ( Figs. 1, 2A, B).

Thoracic sternum relatively narrow ( Figs. 2G, H, 3). Sternites 1, 2 completely fused, no trace of suture; S2/3 complete, deep; S3/4 complete but medially shallow; S4/5,S5/6 medially interrupted; S6/7 medially interrupted by very narrow gap; S7/8 complete; median longitudinal groove on sternites 7, 8 ( Figs. 3, 4I). Somite 3 of male abdomen covers space between P5 coxae, thoracic sternite 8 not visible ( Figs. 4A–D, 5A). Episternites 4–6 laterally expanded ( Figs. 2G, H, 3); episternite 7 expanded laterally and posteriorly, reaching and partially covering anterior part of P5 coxa but not penis ( Figs. 3B, 4G). Penis coxal, small, short distal extension, emerging just anterior to condyle; very broad, soft proximal expansion ( Fig. 4G). Sterno-abdominal cavity relatively deep, reaching to before margin of S3/4 ( Fig. 3). Press button of male abdomen locking mechanism on posterior half of sternite 5, closer to margin of sternite 6 ( Figs. 3, 4E, F).

Male abdomen with 6 freely-movable somites plus telson, relatively narrow; somite 1 exposed, not covered by posterior carapace margin, transversely narrow, sublunate in shape; somites 4–6 sharply decreasing in length from somite 3 (widest somite) ( Figs. 2G, H, 4A–D). Telson elongated, longer than wide or subequal ( Fig. 4E, F). G1 very slender, spinous, pointed apex ( Fig. 5B–D); G2 slightly longer than G1 (slightly shorter in MNHN-B29374), flagellum as long as proximal part, apex truncated ( Fig. 5E).

Female abdomen, with 6 freely-movable somites, relatively narrow, not covering all of thoracic sternum ( Fig. 4H). Telson broadly triangular, wider than long ( Fig. 4H). Somites 1, 2 covering space between P5 coxae, sternite 8 not visible. Vulva of mature females ( Fig. 4I) round, extending from 5/6 suture but not reaching suture 6/7, vulvar cover over ventral half.

Colour. The dorsal surface of the carapace is orange-pink in life, with the legs and ventral surfaces whitish-pink ( Fig. 1). The bodies are usually covered with dirt and mud, and appear black and brown when caught.

Remarks. Rhadinoplax microphthalmus (Guinot & Richer de Forges, 1981) was described from a large male holotype (53.3 x 61.4 mm, MNHN-B 6832; Guinot & Richer de Forges 1981: pl. 6, figs 1, 1a) and eight male and one female paratypes, also of relatively large sizes (33.1 x 37.0 mm to 53.2 x 61.8 mm, MNHN-B 6828-6831, 6833; Guinot & Richer de Forges 1981: pl. 6, figs. 2, 3). All were collected from traps in New Caledonia. The species was subsequently recorded from the Philippines ( Guinot 1989) and Japan ( Matsuzawa 1993).

Almost nothing is known about the ecology of this species. Those in New Caledonia had been collected by traps, while the earlier material from the Philippines were collected by trawls. The good series of recent specimens from Panglao in the Philippines were obtained by tangle nets set in deep water. The fishermen on the island of Balicasag in Panglao set their nets at depths of between 50 to 500 m, and many rare and interesting species have previously been reported from these catches (see Richer de Forges & Ng 2007a –c; Ng et al. in press). The recent specimens of R. microphthalmus obtained were from deep water exceeding 200 m and along the steeper parts (pers. comm. to P. K. L. Ng from fishermen). These areas cannot be effectively trawled or dredged, and in which only traps or tangle nets will work (see also Richer de Forges & Ng 2007c; Ng et al. 2007). Although only 12 specimens of R. microphthalmus are reported here, the second author has seen dozens more specimens, especially large males, which the fishermen had caught, preserved in formalin, dried in the sun and then mounted on cards. The local fishermen at Panglao do this for all large or otherwise strange looking crabs, lobsters and echinoderms. These are then sold to tourists as souvenirs, or collected by traders for bulk export to the U.S., Japan, Russia and Europe (see also Richer de Forges & Ng 2007b).

Distribution. Western Pacific from the Philippine Is. to New Caledonia. Depth: 239– 580 m.