Thyraplax cristata, Castro, 2007

Castro, Peter, 2007, A reappraisal of the family Goneplacidae MacLeay, 1838 (Crustacea, Decapoda, Brachyura) and revision of the subfamily Goneplacinae, with the description of 10 new genera and 18 new species, Zoosystema 29 (4), pp. 609-774 : 677-680

Thyraplax cristata n. sp.

( Figs 20-22 )

Carcinoplax aff. cooki – Poupin 1996a: 98 [in list]; 1996b: pl. 16, fig. b [ French Polynesia].

TYPE MATERIAL. — French Polynesia, SMSRB collections, ♂ holotype, cl 15.1 mm, cw 19.2 mm ( MNHN-B 29801). — SMSRB collections, stn 258, ♀ paratype, cl 14.2 mm, cw 19.1 mm ( MNHN-B 29805). — French Polynesia, SMSRB collections, ♀ paratype, cl 14.9 mm, cw 19.9 mm ( MNHN-B 29806). — French Polynesia, SMSRB collections, ♂ paratype, cl 16.0 mm, cw 20.7 mm ( MNHN-B 16572).

TYPE LOCALITY. — French Polynesia,Tuamotu Archipelago, Fangataufa Atoll, 22°11.7’S, 138°44.3’W, 500 m.

MATERIAL EXAMINED. — French Polynesia. Society Is, SMSRB collections, J. Poupin coll., stn 258, Moorea, 17°31.9’S, 149°53.3’W, trap, 430 m, 18.VI.1990, 1 paratype ♀ ( MNHN-B 29805).

Tuamotu Archipelago, SMSRB collections, Moruroa Atoll, 1984, ♂ paratype ( MNHN-B 16572). — SM- SRB collections, J. Poupin coll., stn D 53, Moruroa Atoll, 21°51.45’S, 139°01.98’W, dredging, 439 m, 17.X.1990, 1 ♀ ( MNHN-B 29804). — Stn 317, Moruroa Atoll, 21°53.8’S, 139°01.6’W, trap, 500 m, 19.X.1990, 1 ♀ ( MNHN-B 29802). — Stn 320, Moruroa Atoll, 21°53.7’S, 138°59.3’W, trap, 510 m, 21.X.1990, 1 ♂ ( MNHN-B 29800). — Stn 323, Fangataufa Atoll, 22°13.2’S, 138°42.7’W, trap, 500 m, 13.X.1990, 2 ♀♀ ( MNHN-B 29817). — Stn 234, Fangataufa Atoll, 22°15.0’S, 138°46.0’W, trap, 250 m, 22.V.1990, 2 ♀♀ ( MNHN-B 29803). — Stn 473, Moruroa Atoll, 21°47.0’S, 138°55.5’W, trap, 465 m, 10.IV.1995, 1 ♀ ( MNHN-B 29807). — Stn 476, Moruroa Atoll, 21°51.3’S, 139°01.2’W, trap, 470 m, 11.IV.1995, ♀ paratype ( MNHN-B 29806). — Stn 485, Fangataufa Atoll, 22°11.7’S, 138°44.3’W, trap, 500 m, 24.IV.1995, ♂ holotype ( MNHN-B 29801).

ETYMOLOGY. — From crista, Latin for “ridge” or “crest”, in reference to the carina-like ridges along the anterolateral borders of the carapace.

DISTRIBUTION. — Known only from French Polynesia (Society Is and Tuamotu Archipelago). Depth: 250- 510 m.

Revision of Goneplacinae ( Crustacea, Brachyura)

DESCRIPTION

Carapace ( Figs 20A ; 21 ; Poupin 1996b: pl. 16, fig. b, as Carcinoplax aff. cooki ) transversely rectangular, slightly wider than long (1.3 as wide as long in holotype), anterolateral borders arched, with thin carina-like crest.Carapace slightly convex, nearly flat, without clear indication of regions. Front lamellar, straight, not marked by median notch. Distinct notch between front, inner edge of supraorbital border. Supraorbital borders sinuous, orbits low on anterior border. Suborbital borders smooth, each with short, blunt inner tooth not visible dorsally. Outer orbital angle with triangular, moderately acute prominence continuing as a carina-like crest to just above anterolateral tooth; weak notch (may be absent on one side) on each anterolateral border halfway between outer orbital angle and anterolateral tooth; thick to slender, acute-tipped anterolateral tooth on each side of carapace. Posterolateral borders long, arched, widest portion of carapace below anterolateral teeth.

Eye peduncles ( Figs 20A ; 21 ) short (0.3 front width), smooth, cornea slightly expanded distally.

Chelipeds (P1) ( Fig. 21 ; Poupin 1996b: pl. 16, fig. b, as Carcinoplax aff. cooki ) nearly equal in males, females, slightly heavier in males; fingers slender, as long as propodus, with blunt teeth, less than half to about three-quarters of distal portion of fingers dark brown. Broad, blunt tooth on inner (ventral), proximal margin of carpus. Ambulatory legs (P2-P5) moderately long, slender, smooth, very few simple setae; length of P5 merus 0.7-0.8 cl; P5 propodus wide, with 2 low carinae on both surfaces; dactyli long, slender, wide carina along both surfaces.

Male abdomen ( Fig. 20B ) broadly triangular, with 6 freely-movable somites plus telson; telson slightly wider than long. Somites 3, 4 slightly inflated near outer margins, somite 3 covers space between P5 coxae; somites 1, 2 slightly narrower than somite 3, thoracic sternite 8 not visible. G1 ( Fig. 20C ) stout, small teeth along outer margin

Castro P.

of distal portion; thick, straight, pointed tip. G2 ( Fig. 20D ) slender, slightly longer than G1, slightly curved flagellum slightly shorter than proximal part (peduncle), pointed tip.

Female abdomen wide.Telson triangular. Somite 3 covers space between P5 coxae, somite 2 only slightly narrower than somite 3, thoracic sternite 8 not visible. Vulva of mature females ( Fig. 22 ) large, extending from edge of anteriorly deflected suture 5/6 to suture 6/7; slightly vaulted (salient in larger females) vulvar cover over outer third of aperture, membrane covers rest of aperture leaving narrow space open along inner margin.

COLOUR

Carapace orange with irregular white spots; chelipeds mostly orange, tips of fingers dark brown, ambulatory legs white, each with two irregular orange spots ( Poupin 1996b: pl. 16, fig. b, as Carcinoplax aff. cooki ).

REMARKS

The new species is closest to T. crosnieri n. comb. from which it can be easily distinguished by its much smaller, more slender, and anteriorly oriented anterolateral teeth (obtuse and dorsally oriented in T. crosnieri n. comb.; Fig. 13C ), ambulatory leg propodi much broader than in T. crosnieri n. comb., straight G1 (bent outwardly in T. crosnieri n. comb.; Guinot & Richer de Forges 1981b: fig. 10I), straight G2 with pointed tip (bent with two spinules in T. crosnieri n. comb.; Guinot & Richer de Forges 1981b: fig. 10L), vulva with a vaulted vulvar cover on its outer margin (in T. crosnieri n. comb. the vulvar cover is large and salient, covering most of the crescent-shaped vulva; triangular and posterior in small mature females; Fig. 19 ).

Differences between the T. cristata n. sp. and T. truncata n. sp., a similar but small-size species, are discussed in the description of the latter. Differ- ences between all five species of Thyraplax n. gen. are summarized in Table 3.

Figures

FIG. 20. — Thyraplax cristata n. sp., ♂ holotype,cl 15.1 mm, cw 19.2 mm,Fangataufa Atoll, French Polynesia,SMSRB collections, stn 485, 500 m (MNHN-B 29801): A, dorsal surface of the carapace; B, abdomen; C, left G1, dorsal view; D, left G2, ventral view. Scale bars: A, 5 mm; B, 3 mm; C, D, 1 mm.

FIG. 21. — Thyraplax cristata n. sp., ♂ holotype, cl 15.1 mm, cw 19.2 mm, Fangataufa Atoll, French Polynesia, SMSRB collections, stn 485, 500 m (MNHN-B 29801).

FIG. 22. — Thyraplax cristata n. sp., ♀ paratype, cl 14.9 mm, cw 19.9 mm, Moruroa Atoll, French Polynesia, SMSRB collections, stn 476, 470 m (MNHN-B 29806), thoracic sternum, vulva, and vulvar cover.

FIG. 13. — A, Pycnoplax surugensis (Rathbun,1932) n. comb., ♂, cl 14.7 mm, cw 20.6 mm,off southern coast of New Caledonia,BATHUS 2, stn DW 719,22°47.57’S,167°14.58’E,444-455 m (MNHN-B 29412);B, Pycnoplax bispinosa (Rathbun, 1914) n. comb., ♀, cl 9.0 mm, cw 11.2 mm,off Rendova I., SALOMON 2,stn CP 2287,253-255 m (MNHN-B 30088);C, Thyraplax crosnieri (Guinot & Richer de Forges, 1981) n. comb., ♀, cl 10.6 mm, cw 13.5 mm, off southern coast of New Caledonia, MUSORSTOM 4, stn DW 222, 410-440 m (MNHN-B 29422).

FIG. 19. — Thyraplax crosnieri (Guinot & Richer de Forges, 1981) n. comb., ♀, cl 16.7 mm, cw 21.9 mm, Balicasag I., off Panglao I., Philippine Is, 50-500 m (ZRC 2004.0720), thoracic sternum, vulva, and vulvar cover.