Carcinoplax uncinata, Castro, 2009
Castro, Peter, 2009, Two new species of Carcinoplax H. Milne Edwards, 1852, and Pycnoplax Castro, 2007, from the western Pacific, and a description of the female of Thyraplax truncata Castro, 2007 (Crustacea, Decapoda, Brachyura, Goneplacidae), Zoosystema 31 (4), pp. 949-957 : 950-952
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( Fig. 1 View FIG )
TYPE MATERIAL. — New Caledonia. LAGON NORD, stn 500, 19°04’S, 163°30’E, 225 m, 4.III.1985, ♂ holotype, cl 6.5 mm, cw 8.4 mm ( MNHN-B 30809). — Grand Récif Sud, stn 387, 22°39’S, 167°07’E, 225 m, 22.I.1985, 1 ♀ paratype, cl 6.5 mm, cw 8.5 mm ( MNHN-B 30829).
Solomon Is. SALOMON 1, stn CP 1849, north of San Cristobal I., 10°28.2’S, 161°59.3’E, 230 m, 6.X.2001, 1 ♀ paratype, cl 10.2 mm ( MNHN-B 30810).
BATHUS 2, stn DW 715, 22°39.42’S, 167°26.84’E, 202-277 m, 10.V.1993, 1 ♀ paratype, cl 7.7 mm, cw 10.0 mm ( MNHN-B30838 ).— GoogleMaps Stn DW 726, 22°47.30’S, 167°28.74’E, 241-260 m, 12. V.1993,1 ♂ paratype, cl 5.6 mm, cw 6.8 mm; 1 ♀ paratype, cl 7.0 mm, cw 9.4 mm ( ZRC 2008.1337 View Materials ) GoogleMaps .
TYPE LOCALITY. — Off the north coast of New Caledonia, 19°10’S, 163°35’E, 225 m.
OTHER MATERIAL EXAMINED. — New Caledonia. LAGON NORD, stn 516, 19°10’S, 163°35’E, 48 m, 5.III.1985, 1 ♀, cl 6.9 mm, cw 9.1 mm ( MNHN-B 30830).
MUSORSTOM 5, stn 335, 20°03.24’S, 153°45.35’E, 315 m, 15.X.1986, 1 ♂, cl 6.1 mm, cw 7.7 mm (MNHN-B30831). — Stn 346, 19°39.77’S, 158°27.07’E, 245-
252 m, 17.X.1986, 1 pre-adult ♀, cl 5.6 mm, cw 7.4 mm,? 1 pre-adult cl 3.1 mm, cw 3.8 mm (MNHN-B30832). — Stn 348, 19°36.00’S, 158°31.70’E, 260 m, 17.X.1986, 1 ♀, cl 6.9 mm, cw 8.9 mm (MNHN-B30833). — Stn 377, 19°48.60’S, 150°29.10’E, 260-270 m, 20.X.1986, 1 ♀, cl 6.9 mm, cw 8.9 mm (MNHN-B30834).
BATHUS 2, stn DW 715, 22°39.42’S, 167°26.84’E, 202-277 m, 10.V.1993, 2 ♀♀, cl 7.1 mm, cw 9.1, cl 6.4 mm, cw 7.7 mm (MNHN-B30837).— Stn DW 726, 22°47.30’S, 167°28.74’E, 241-260 m, 12.V.1993, 1 ♂, cl 5.0 mm, cw 5.8 mm (MNHN-B30790). — Stn DW 727, 22°48.03’S, 167°29.03’E, 299-302 m, 12.V.1993, 1 ♀, cl 5.9 mm, cw 7.4, 1 pre-adult ♀, cl 5.0 mm, cw 6.2 mm (MNHN-B30835). —? Stn DW 723, 22°50.21’S, 167°26.84’E, 430-433 m, 11.V.1993, 1 pre-adult ♀, cl 4.1 mm, cw 5.1 mm (MNHN-B30836).
ETYMOLOGY. — From uncus, Latin for “hook”, for the diagnostic shape of the first anterolateral teeth, which are separated from the outer orbital teeth by a deep, narrow, J-shaped gap.
DISTRIBUTION. — Western Pacific Ocean : Solomon Is and New Caledonia. Depth: 202-315 m. One specimen was collected from 48 m close to the type locality ; a pre-adult of questionable identification from 430-433 m.
Carapace ( Fig. 1A View FIG ) quadrate, slightly wider than long (1.3 as wide as long in male holotype). Carapace slightly convex, without clear indication of regions; dorsal surface smooth, microscopically granular (small granules along anterolateral borders in largest female paratype; MNHN-B30810); slight depression across cardiac region, slight elevations on each branchial region, giving appearance of 2 transversal carinae across carapace. Front lamellar, straight, not marked by median notch. Slight notch between front, inner edge of supraorbital border. Supraorbital borders sinuous, without notches (slight median notch in largest female paratype; MNHN-B30810), borders microscopically granular. Suborbital borders granular, each with short, blunt inner tooth not visible dorsally. Outer orbital angle with broad, rounded, anteriorly projecting, slightly asymmetrical, smooth tooth; deep, narrow, J-shaped gap between outer orbital, first anterolateral tooth; 2 smooth anterolateral teeth on each side of carapace; first (anteriormost) anterolateral tooth curved, hook-like, with variously acute tip, slightly dorsally projecting; second (posteriormost) anterolateral tooth triangular, with acute tip, dorsally projecting; margin between anterolateral teeth nearly straight, granular. Posterolateral borders slightly arched. Posterior margin slightly arched, slightly longer than front, with scattered, short plumose setae.
Subhepatic, pterygostomial regions, pterygostomial crest slightly granular (larger granules in largest female paratype; MNHN-B30810). Third maxillipeds completely close buccal cavern; merus auricular. Anterior border of endostome well demarcated from buccal cavern, ridges faint but clearly defined. Particularly short tomentum on surface of thorax, abdomen (absent in largest female paratype); plumose setae along outer margin of thorax.
Eye peduncles ( Fig. 1A View FIG ) short (0.1 front width), dorsal surface granular, cornea slightly expanded distally. Orbits narrow, not expanded distally.
Chelipeds (P1) nearly equal in both males (right slightly thicker in holotype; Fig. 1A View FIG ) and females, much thicker propodus in males; fingers slender in females, much longer than propodus (stouter in males), with blunt teeth, one-third to one-half distal portion of fingers dark brown. Outer surface with microscopic granules; few simple setae on carpus, patch of short plumose setae on inner (ventral) margin of propodus (absent in largest female paratype). Broad, curved, acute-tipped tooth on inner (ventral), proximal margin of carpus. Ambulatory legs (P2-P5) relatively short, distal end of P5 merus just reaching second anterolateral tooth when folded, articles unarmed; long as well as short, simple setae along margins of articles; long, simple setae along inner margin of P5 propodus. P5 dactylus long, slender, unarmed; length of P5 merus 0.4 cl.
Median sulcus present on thoracic sternites 7-8; sutures 4/5, 5/6, 6/7, 7/8 medially interrupted ( Fig. 2E View FIG ).
Male abdomen ( Fig. 1B View FIG ) narrowly triangular, with 6 freely-movable somites plus telson; telson slightly longer than wide. Abdominal-locking mechanism with medium-size button on edge of thoracic sternite 5 pairing with shallow socket on underside (ventral surface) of abdominal somite 6. Somite 3 covers space between P5 coxae, episternite 7, outer edge of somite not fitting under episternite; somites 1, 2 as wide as somite 3, thoracic sternite 8 not visible when abdomen closed. Penis emerging from coxal gonopore, protected by episternite 7. G1 ( Fig. 1C View FIG ) long, slender, dorsoventrally flattened, straight, only slightly broadened proximally, small denticles on distal portion; truncated apex with slightly pointed outer margin. G2 ( Fig. 1D View FIG ) slender, not as long as G1, slightly curved flagellum slightly shorter than proximal part (peduncle), apex with 2 lateral spinules.
Female abdomen wide, fringed by long, plumose setae. Telson wider than long. Somites 2, 3 cover space between P5 coxae, small portion of thoracic sternite 8 visible when abdomen closed. Vulva of mature female ( Fig. 2E View FIG ) large, oblong, much expanded, extending from close to deflected suture 5/6 to close to deflected suture 6/7; membrane covers aperture, leaving narrow space open along anterior margin, sternal vulvar cover absent.
The new species shows all of the characters that are diagnostic of the 18 previously described species of Carcinoplax , most importantly the presence of a long, slender, dorsoventrally flattened G1 with a thin, truncated apex, a particularly large vulva that extends from suture 5/6 to suture 6/7, and which is covered by a soft membrane and not by a sternal vulvar cover (see Castro 2007: 623). Among its congeners, it is closest to C. specularis Rathbun, 1914 , in the overall appearance of the carapace (see Guinot 1989: pl. 8, figs A, B; pl. 9, figs D, E, as C. verdensis Rathbun, 1914 ; pl. 8, figs E, F, as C. polita Guinot, 1989 ), the G1 and G2 (see Guinot 1989: fig. 34; fig. 37, as C. polita Guinot, 1989 ), and, in most specimens, the presence of a short tomentum on the surface of the thorax and abdomen. In C. uncinata n. sp., however, the outer orbital teeth are larger and with a more prominent anterior margin than in C. specularis , and there is a narrow, J-shaped gap between the outer orbital and the first anterolateral tooth, which is curved and hook-like. This is in contrast to C. specularis , where there is a wider, U-shaped gap between the outer orbital and first anterolateral teeth, and the tip of the first anterolateral tooth is not as anteriorly advanced as in C. uncinata , and hence not noticeably hook-shaped (see Guinot 1989: fig. 25; fig. 22, as C. verdensis ; fig 24, as C. polita ). There is also a patch of short plumose setae on the inner (ventral) margin of the cheliped propodus of C. uncinata n. sp. (but absent in the largest female paratype; MNHN-B30810), which is absent in C. specularis , and the cheliped fingers of females are visibly more slender in C. uncinata n. sp. than in C. specularis .
The general structure of the carapace (except the diagnostic shape of the outer orbital and anterolateral teeth), G1, G2, and vulva of the new species can be observed in other species of Carcinoplax , but there are important differences when contrasted with congeners. In C. abyssicola ( Miers, 1886) , the outer orbital margin is flat, nearly horizontal, and posteriorly inclined (see Miers 1886: pl. 19, fig. 2; Guinot 1989: fig. 38, pl. 9, figs A, B). In C. cracens Castro, 2007 , the walking legs are much longer and slender than in the new species (see Castro 2007: fig. 3), a difference that also applies to C. longipes (Wood-Mason, 1891). In C. inaequalis ( Yokoya, 1933) , there are two conspicuous, wide horizontal ridges on the dorsal surface of carapace, the outer orbital teeth are only slightly inclined dorsally, and the anterolateral teeth are more straight and slender than in the new species. These characters are unfortunately not apparent in Yokoya’s figure ( Yokoya 1933: fig. 63) but are distinctively shown in the type material (see Castro 2007: 633).
There is some variation in the shape of the anterolateral teeth among individuals of the new species. The first and second teeth can be obtuse in some specimens but usually on only one side, the teeth on the opposite side being acute as in most specimens.
Carcinoplax uncinata n. sp. appears to be a smallsize species, the largest of the 18 specimens examined being a female with a carapace length of only 10.2 mm (MNHN-B30810). In contrast, large-size species such as C. longimana (de Haan, 1833) , carapace length may reach well over 50 mm ( Guinot 1989). The new species raises the number of described species of Carcinoplax , the largest genus of the family Goneplacidae , to 19.
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