Carcinoplax H. Milne Edwards, 1852

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 : 622-625

Genus Carcinoplax H. Milne Edwards, 1852

Curtonotus de Haan, 1833: 4 , 20, 233 [as subgenus without nominal species, name preoccupied by Curtonotus Stephens, 1827 (Coleoptera) ]. — Dana 1851: 285 [diagnosis]; 1852: 310 [diagnosis], 1493 [in list].

Carcinoplax H. Milne Edwards, 1852: 164 [replacement name]. — Ortmann 1894: 685 [in key]; 1898: 1176 [in list] (part). — Alcock 1899: 70 [diagnosis]; 1900: 292 [in list], 298 [in key], 301. — Stebbing 1905: 37 [discussion]. — Tesch 1918: 154 (part). — Balss 1922: 135; 1957: 1656 (part). — Sakai 1939: 555 [in key], 555; 1969: 269; 1976: 523 [in key] (part). — Barnard 1950: 282 [in key], 286 [diagnosis] (part). — Imaizumi 1960: 219; 1961: 162, 163 [fossils]. — Serène 1968: 89 [in list] (part). — Guinot 1969a: 246 [discussion]; 1969b: 520, 524 [discussion]; 1971: 1081 [list of species]; 1989: 273 [revision] (part). — Glaessner 1969: R526 [diagnosis]. — Serène & Lohavanijaya 1973: 62, 63 [key to species] (part). — Chen 1984: 188; 1998: 266 [key to species] (part). — Dai et al. 1986: 366 [key to species] (part). — Dai & Yang 1991: 394 [key to species] (part). — Hsueh & Huang 2002: 116 [in key], 119 [key to species] (part). — Davie 2002: 193 (part). — Karasawa & Kato 2003b: 130 [in list], 140 [in list], 141 [in table] (part). — Poore 2004: 434 (part). — Karasawa & Schweitzer 2006: 26 [in list], 40 (part). — Ng & Manuel-Santos 2007: 42 [discussion].

Not Carcinoplax – A. Milne-Edwards 1873: 267 (= Heteropilumnus De Man, 1895 ).

TYPE SPECIES (of Curtonotus ). — Cancer (Curtonotus) longimana de Haan, 1833 (subsequent designation by Glaessner [1929]; gender feminine).

EXTANT SPECIES INCLUDED . — Carcinoplax abyssicola ( Miers, 1886) ; C. confragosa Rathbun, 1914 ; C. cracens n. sp.; C. inaequalis ( Yokoya, 1933) ; C. indica Doflein, 1904 ; C. ischurodous ( Stebbing, 1923) ; C. longimana (de Haan, 1833) ; C. longipes (Wood-Mason, 1891) ; C. monodi Guinot, 1989 ; C. nana Guinot, 1989 ; C. purpurea Rathbun, 1914 ; C. sinica Chen, 1984 ; C. specularis Rathbun, 1914 ; C. spinosissima Rathbun, 1914 ; C. tenuidentata n. sp.; C. tomentosa Sakai, 1969 ; C. tuberosa n. sp.; C. velutina n. sp.

All species are restricted to the Indo-West Pacific region; some also found in subtemperate areas contiguous to the Indo-West Pacific region.

FOSSIL SPECIES INCLUDED ( Karasawa & Kato [2003b]). — Carcinoplax antiqua (Ristori, 1889) ; C. granulimanus Karasawa & Inoue, 1992 ; C. imperfecta Karasawa & Inoue, 1992 ; C. mongosungi Hu &Tao, 1985 ; C. proavita (Glaessner, 1960) ; C. prisca Imaizumi, 1961 ; C. sp. aff. C. purpurea Rathbun, 1914 ( Karasawa & Kato 2003b); C. shukumi Hu & Tao, 1985 ; C. temikoensis Feldmann & Maxwell, 1990 ; C. thongi Hu &Tao, 1985 ; C. tsengi Hu &Tao, 1996 ; Carcinoplax sp. (Feldmann & Keyes 1992); Carcinoplax sp. (Karasawa 1997); Carcinoplax sp. (Kato 1996).

SPECIES NOT INCLUDED IN CARCINOPLAX . — Carcinoplax angusta Rathbun, 1914 (in yet undescribed genus in the family Euryplacidae ; see Remarks).

Carcinoplax barnardi Capart, 1951 (in Goneplax Leach, 1814 ).

Carcinoplax eburnea Stimpson, 1858 (type material lost and never figured; perhaps a synonym of the portunid Libystes nitidus A. Milne-Edwards, 1867 (see Serène & Lohavanijaya [1973: 62]).

Carcinoplax microphthalmus Guinot & Richer de Forges, 1981 (in yet undescribed genus with affinities to the family Euryplacidae ; see Remarks).

DIAGNOSIS. — Carapace transversely rectangular, wider than long, or quadrate, only slightly wider than long; widest at junction of anterolateral, posterolateral borders; front lamellar, straight, very rarely marked by slight median notch or projection (in C. confragosa ). Notch between front, inner edge of supraorbital border distinct, very slight, or absent; orbits narrow, not expanded distally; supraorbital borders slightly sinuous; suborbital borders rounded, with short, blunt inner tooth not visible dorsally; anterolateral borders convex. Dorsal surface of carapace typically smooth (slight horizontal ridges in some species), moderately convex, without clear indication of regions. Outer orbital angle with tooth, elongated prominence, or unarmed; 2 (3 in rare cases when outer orbital tooth detached from outer orbital angle is included ; one in C. ischurodous ) anterolateral teeth on each side of carapace (no teeth in large specimens of few species). Basal antennal article short, slender, distalmost (third) article reaches front. Eye peduncles short, much shorter than front (0.2-0.3 front width); cornea spherical, only slightly expanded distally. No obvious stridulating mechanism other than possible rubbing of proximal portion of cheliped (P1) merus against pterygostomial ridge. Thoracic sternum wide. Median sulcus on thoracic sternite 4 absent; sutures 4/5, 5/6, 6/7, 7/8 interrupted medially ( Fig. 1 ). Anterior end of sterno-abdominal cavity anterior to thoracic sternite 4. Cheliped fingers moderately slender or thick, shorter than propodus, darker in colour in most species; carpus with tooth on inner margin. Dorsal margins of meri, carpi, propodi of ambulatory legs (P2-P5) unarmed (except P2 merus of C. spinosissima ); dactyli slender, smooth, setose. Male abdomen with 6 freely-movable somites plus telson, narrowly triangular, somites 4-6 gradually decreasing in width from somite 3 (widest somite). Telson about as long as wide. Somite 3 covers space between P5 coxae, somite 2 slightly narrower than or as narrow as somite 3 so that somites 1, 2 leave small, often triangular portion of thoracic sternite 8 visible ( Guinot 1969b: fig. 61; 1989: fig. 2; Hsueh & Huang 2002: figs 7B, 9C, 10B), or somite 2 much narrower than somite 3 leaving a larger portion of thoracic sternite 8 visible ( C. monodi ; see Guinot 1969b: fig. 65, as C. indica ; Guinot 1989: fig. 3). G1 long, slender, thin, straight or slightly sinuous, only slightly broadened proximally; truncated or pointed, thin tip. G2 slender, slightly longer than or as long as G1, flagellum shorter than proximal part (peduncle), slightly-expanded tip with 1 or 2 (rarely 3) spinules. Penis arising from P5 coxa, moderate size; broad, soft proximal expansion. Female abdomen with 6 freelymovable somites, wide. Telson wider than long. Somite 3 covers space between P5 coxae, somite 2 narrower than somite 3 so that somites 1, 2 leave small, often triangular portion of thoracic sternite 8 visible, or somite 2 as wide as somite 3 so that thoracic sternite 8 not visible. Vulva of mature females ( Fig. 1 ) greatly expanded, extending from suture 5/6 to suture 6/7, covered by soft membrane, vulvar cover absent.

REMARKS

The history of the genus Carcinoplax was summarized by Serène & Lohavanijaya (1973: 62) and Guinot (1989: 267). The genus was described as Curtonotus by de Haan (1833) for Curtonotus longimanus and C. vestitus (= Entricoplax vestita n. comb.), both from Japan. Curtonotus was preoccupied and consequently replaced by Carcinoplax by H. Milne Edwards (1852: 164). Additional species were described, which were progressively listed by Tesch (1918) and Balss (1957). The status of some of the species remained questionable, mostly because of changes in the shape of the carapace and the size of the chelipeds (P1) with age. Barnard (1950: 287), for instance, doubted the validity of the seven species from the Philippine Is described by Rathbun (1914). Serène & Lohavanijaya (1973: 63) commented on the status of some of the species and gave a key to 17 species, of which seven do not belong to Carcinoplax sensu stricto, one ( C. verdensis Rathbun, 1914 ) proved to be a junior synonym of another ( C. specularis Rathbun, 1914 ), and a ninth species ( C. angusta Rathbun, 1914 ) actually belongs in another family.

The heterogeneous nature of the genus was recognized by earlier workers. Sakai (1969: 269) recognized three groups among the 17 species he listed but solely based on the morphology of the orbits and the anterolateral teeth. This was a very artificial grouping since species with very different G1, G2, male abdomens, and vulvae were placed together in the same groups. Guinot (1969b: 524) similarly recognized three groups (plus the unique status of some species), which were different from those of Sakai (1969). Although far more significant characters such as the G1, male abdomens, and thoracic sternites were considered, it was concluded that it was premature to create sub-generic or other taxa (“catégories sousgénériques ou autres”) for the genus since several species had not been examined by her. Guinot (1989) made the only revision of the genus so far, listing a total of 28 species, seven of which were not examined.

The status of several species described under Carcinoplax nevertheless remained problematic. Serène & Vadon (1981: 127) listed two unidentified species that presumably were new. Their Carcinoplax sp. A appears to indeed belong in Carcinoplax based on their description of the G1. Carcinoplax sp. B, however, most probably belonged in Pycnoplax n. gen. because, as pointed out ( Serène & Vadon 1981: 127), the G1 was of the same type as that of C. bispinosa Rathbun, 1914 (= Pycnoplax bispinosa n. comb.) and C. surugensis Rathbun, 1932 (= P. surugensis n. comb.). No “ Carcinoplax sp. A and B” specimens could be found in the MNHN collections.

Carcinoplax angusta Rathbun, 1914 does not belong to Carcinoplax sensu stricto. This species was described from specimens collected in the Philippine Is, a female holotype (23.8 × 27.6 mm, USNM 46166; see Guinot 1989: fig. 39, pl. 12, figs A-E) and a pre-adult male (10 × 10.8 mm, same catalogue number). Most of the unique characters that separate C. angusta from Carcinoplax sensu lato were nevertheless clearly outlined by Rathbun (1914: 142): narrow male abdomen; slightly bilobed front; oblique supraorbital borders; sub octagonal, convex carapace; inner margin of suborbital bor- der with a “very large and prominent” tooth; and two small anterolateral teeth (first being a “blunt tooth or large tubercle”). The G1 is slender and the distal portion provided with small spinules ( Zarenkov 1972: fig. 6-4; Guinot 1989: fig. 39D; Chen 1998: fig. 6-7, as C. angustata [sic]) and the G2 is much shorter than the G1 ( Chen 1998: fig. 6-8, as C. angustata [sic]). The sterno-abdominal cavity of males is conspicuously deep. The penis is relatively long, much longer than in Carcinoplax , and it lies in a concave thoracic sternite 8 before joining the G1. The thoracic sternite 8 is not visible from dorsal view. Females have a relatively narrow abdomen and the vulva is large and round (though not as large as in Carcinoplax ) and surrounded by a thick lip. All of these characters clearly separate C. angusta from other species of Carcinoplax sensu stricto and from the other goneplacine genera being described as new. These characters support the inclusion of C. angusta in the family Euryplacidae (see Table 2).

A species morphologically similar to C. angusta , C. microphthalmus Guinot & Richer de Forges, 1981 , was described from a very large male holotype (53.3 × 61.4 mm, MNHN-B 6832; Guinot & Richer de Forges 1981a: pl. 6, figs 1, 1a) and eight male and one female paratypes, also of large size (33.1 × 37.0 mm to 53.2 × 61.8 mm, MNHN-B 6828-6831, 6833; Guinot & Richer de Forges 1981a: pl. 6, figs 2, 3), all from New Caledonia.

Carcinoplax microphthalmus differs from Carcinoplax sensu stricto and from other new goneplacine genera in having a narrow male abdomen ( Guinot & Richer de Forges 1981b: fig. 9C), very slender and long G1 with a pointed tip ( Guinot & Richer de Forges 1981b: fig. 10E-G), and a relatively narrow female abdomen, all suggesting affinities to the Euryplacidae . The G2, however, is as long as or slightly longer than the G1 ( Guinot & Richer de Forges 1981b: fig. 10H) as in Carcinoplax sensu stricto, although the flagellum is as long as the proximal part, not shorter as in Carcinoplax . Also unlike Carcinoplax is a small vulva that is partially covered by a thick vulvar cover, a structure that appears to be absent among euryplacids. Other differences from typical euryplacids are the absence of many small denticles on the G1 and a penis that is not long and protected by a concave thoracic sternite 8. The thoracic sternite is not visible dorsally as in euryplacids. The taxonomic position of C. microphthalmus thus remains uncertain in anticipation of a revision of the Euryplacidae and related genera still in progress.

Figures

FIG. 1. — Carcinoplax longimana (de Haan, 1833), ♀, cl 29.1 mm, cw 37.8 mm, off northeastern Taiwan, TAIWAN 2001, stn CP 81, 205 m (MNHN-B 29648), thoracic sternum and vulva.