Thyraplax digitodentata, 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 : 681-683

Thyraplax digitodentata n. sp.

( Figs 23 ; 24 )

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

TYPE MATERIAL. — ♂ holotype, cl 8.8 mm, cw 10.8 mm, SMSRB collections, French Polynesia ( MNHN-B 29433 ) ; ♂ paratype, cw 11.3 mm, SMSRB collections, French Polynesia ( MNHN-B 29799 ) .

TYPE LOCALITY. — French Polynesia,Tuamotu Archipelago, Moruroa Atoll, 21°47.7’S, 138°56.1’W, 560 m.

MATERIAL EXAMINED. — French Polynesia. Tuamotu Archipelago, SMSRB collections, J. Poupin coll., Moruroa Atoll, 21°47.7’S, 138°56.1’W, cage, 560 m, 2.XII.1989, ♂ holotype ( MNHN-B 29433). — Stn 242, Maria Is, 22°00.0’S, 136°12.0’W, cage, 670 m, 30.V.1990, ♂ paratype ( MNHN-B 29799).

ETYMOLOGY. — From digitus, Latin for “finger”, and dens, Latin for “tooth”, in reference to the diagnostic P5 dactylus that is armed with minute teeth.

DISTRIBUTION. — Known only from the Tuamotu Archipelago, French Polynesia. Depth: 560- 670 m.

Castro P.

DESCRIPTION

Carapace ( Figs 23A ; 24 ; Poupin 1996b: pl. 16, fig. c, as Carcinoplax aff. crosnieri ) transversely rectangular, slightly wider than long (1.2 as wide as long in holotype), anterolateral borders arched, with a slight carina-like crest. Carapace slightly convex, without clear indication of regions. Front lamellar, straight, not marked by median notch. Notch between front, inner edge of supraorbital border absent. Supraorbital borders sinuous, orbits low on anterior border. Suborbital borders granular, each with short, blunt inner tooth not visible dorsally. Outer orbital angle with triangular, moderately acute prominence continuing as a slight carina-like crest to just above anterolateral tooth; anterolateral border without notch or slight tooth between outer orbital angle and anterolateral tooth; single short, slender, acute-tipped anterolateral tooth on each side of carapace. Posterolateral borders long, arched, widest portion of carapace below anterolateral teeth.

Eye peduncles ( Figs 23A ; 24 ) short (0.3 front width), smooth, cornea slightly expanded distally.

Chelipeds (P1) ( Fig. 24 ; Poupin 1996b: pl. 16, fig. c, as Carcinoplax aff. crosnieri ) nearly equal (female unknown); fingers thick, as long as thick propodus, with blunt teeth, completely dark brown. Carpus, merus short, thick; 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 cl (holotype); propodi narrow, smooth; dactyli long, slender; P5 dactylus ( Fig. 23B ) with slender spines along anterior, posterior borders.

Male abdomen ( Fig. 23C ) narrowly triangular, with 6 freely-movable somites plus telson; telson longer than wide. Somite 6 longer than 5, somite 3 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. 23D ) stout but slender distally, minute teeth along margins; bent, keel-like distal portion, pointed tip. G2 ( Fig. 23E ) slender, slightly longer than G1, slightly curved flagellum shorter than basal part, tip with long, lateral spinule.

Female unknown.

COLOUR

Carapace, chelipeds, and ambulatory legs white, tips of fingers black ( Poupin 1996b: pl. 16, fig. c, as Carcinoplax aff. crosnieri ).

REMARKS

The new species is known from only two male specimens, in one of which the dorsal surface of the carapace is damaged. The two specimens are so different from the other four known species of Thyraplax n. gen., however, that they warrant their description as a new species.

Thyraplax digitodentata n. sp. is closest to T. cristata n. sp. in the general shape of the carapace. The P5 dactylus of T. digitodentata n. sp. has a smooth surface with minute teeth along the margins ( Fig. 23B ) (carinated surface without teeth or setae in T. cristata n. sp.), the suborbital border is granular (smooth in T. cristata n. sp.), G1 with thin distal portion with denticles only along margins ( Fig. 23D ) (thick tip with denticles along surface of distal portion in T. cristata n. sp.; Fig. 20C ), G2 with one pointed, lateral spinule on its tip ( Fig. 23E ) (tip pointed in T. cristata n. sp.; Fig. 20D ), and noticeably narrower male abdomen ( Fig. 23C ) than in T. cristata n. sp., the telson being longer than wide in contrast to wider than long in T. cristata n. sp. ( Fig. 20B ).

Differences between the new species and the other species of Thyraplax n. gen. are summarized in Table 3.

Figures

FIG. 23. — Thyraplax digitodentata n. sp., ♂ holotype, cl 8.8 mm, cw 10.8 mm, SMSRB collections, Moruroa Atoll, French Polynesia, 560 m (MNHN-B 29433):A, dorsal surface of the carapace;B, right P5 dactylus; C, abdomen;D, left G1, dorsal view;E, left G2,ventral view. Scale bars: A, 5 mm; B, 1 mm; C, 3 mm; D, E, 1 mm.

FIG. 24. — Thyraplax digitodentata n. sp., ♂ holotype, cl 8.8 mm, cw 10.8 mm, SMSRB collections, Moruroa Atoll, French Polynesia, 560 m (MNHN-B 29433).

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.