Thyraplax truncata, 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 : 683-685

Thyraplax truncata n. sp.

( Figs 25 ; 26 )

TYPE MATERIAL. — BORDAU 1, stn CP 1481, ♂ holotype, cl 8.7 mm, cw 11.6 mm ( MNHN-B 29547). Specimen with a rhizocephalan parasite ( Thompsonia sp.) on P1-P4 and gonopods. Paratypes: 4 ♂♂ (including 1 pre-adult) from New Caledonia as listed under Material examined.

TYPE LOCALITY. — Fiji, Lau submarine ridge, 20°57’S, 178°45’W, 441- 506 m.

MATERIAL EXAMINED. — New Caledonia. SMIB 3, stn DW 22, 23°03’S, 167°19.1’E, 503 m, 24.V.1987, 1 ♂ paratype, cl 7.0 mm, cw 8.9 mm ; 1 ♂ paratype, parasitised by Sacculina , cl 7.2 mm, cw 9.2 mm ( MNHN-B 29473 ) .

BERYX 11, stn CP 21, 24°44’S, 168°07’E, 430-450 m, 17.X.1992, 1 ♂ paratype, cl 7.1 mm, cw 9.1 mm ( MNHN-B 29545).

BATHUS 2, stn DW 719, 22°47.57’S, 167°14.58’E, 444-445 m, 11.V.1993, 1 pre-adult ♂ paratype, cl 5.6 mm, cw 7.0 mm (MNHN-B 29546).

Fiji. BORDAU 1, stn CP 1481, 20°57’S, 178°45’W, 441- 506 m, 9.III.1999, ♂ holotype, parasitised by Thompsonia , cl 8.7 mm, cw 11.6 mm ( MNHN-B 29547).

ETYMOLOGY. — From truncus, Latin for something that has been “maimed” or “cut off”, in reference to the attenuated shape of the G1 diagnostic of the species.

DISTRIBUTION. — Known only from New Caledonia and Fiji. Depth: 430- 500 m.

DESCRIPTION

Carapace ( Figs 25A ; 26 ) 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 short carina-like crest to just above anterolateral tooth; slight notch on each anterolateral border halfway between outer orbital angle and anterolateral tooth; slender, acutetipped anterolateral tooth on each side of carapace. Posterolateral borders long, arched, widest portion of carapace behind anterolateral teeth.

Eye peduncles ( Figs 25A ; 26 ) short (0.3 front width), smooth, cornea slightly expanded distally.

Chelipeds (P1) ( Fig. 26 ) nearly equal (female unknown); fingers slender, about half propodus length, with blunt teeth, less than half to about three-quarters of distal portion of fingers dark brown. Broad, blunt, slightly curved tooth on inner (ventral), proximal margin of carpus. Ambulatory legs (P2-P5) moderately long, slender, smooth, very few simple setae; length of P5 merus 0.6-0.7 cl; P5 propodi wide, smooth; dactyli long, slender, smooth.

Male abdomen ( Fig. 25B ) broadly triangular, with 6 freely-movable somites plus telson; telson slightly wider than long. Somite 3 covers space between P5 coxae; somites 1, 2 slightly narrower than somite 3, thoracic sternite 8 not visible. G1 ( Fig. 25C ) stout, minute teeth along margins of distal portion; truncated tip. G2 ( Fig. 25D ) slender, slightly longer than G1, slightly curved flagellum shorter than proximal part (peduncle), tip slightly expanded with 1 lateral spinule.

Female unknown.

REMARKS

The new species is known from only five small males from New Caledonia and Fiji. They are all close to T. cristata n. sp., which is known from larger specimens from French Polynesia, except for some significant characters: G1 with numerous, minute teeth along the distal portion and a truncated tip ( Fig. 25C ) (G1 of T. cristata n. sp. with many denticles along the distal portion and a thick, pointed tip; Fig. 20C ), G2 having a tip with one long, lateral spinule ( Fig. 25D ) (G2 of T. cristata n. sp. with a simple, pointed tip; Fig. 20D ), and smooth P5 propodus and dactylus (propodus and dactylus with two low carinae on both surfaces in T. cristata n. sp.). Abdominal somites 3 and 4 lack the slightly inflated region near the outer margins characteristic of T. cristata n. sp. The fully formed G1 (which is simpler in the smallest specimen, cl 5.6 mm, cw 7.0 mm [MNHN-B 29546]) and the presence of different G2 precludes the possibility

Revision of Goneplacinae ( Crustacea, Brachyura)

that the new species may actually represent the pre-adult of T. truncata n. sp.

Differences between T. truncata n. sp. and the remaining four species of Thyraplax n. gen. are summarized in Table 3.

Figures

FIG. 25. — Thyraplax truncata n. sp., ♂ holotype, cl 8.7 mm, cw 11.6 mm, Fiji, BORDAU 1, stn CP 1481, 441-506 m (MNHN-B 29547): A, dorsal surface of the carapace; B, abdomen; C, left G1 (with rhizocephalan parasite, Thompsonia sp.), dorsal view; D, left G2 (with rhizocephalan parasite, Thompsonia sp.), ventral view. Scale bars: A, 5 mm; B, 3 mm; C, D, 1 mm.

FIG. 26. — Thyraplax truncata n. sp., ♂ holotype, cl 8.7 mm, cw 11.6 mm, Fiji, BORDAU 1, stn CP 1481, 441-506 m (MNHN-B 29547), specimen with a rhizocephalan parasite (Thompsonia sp.) on P1-P4.

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.