Pycnoplax, 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 : 661-662

Genus Pycnoplax n. gen.

Carcinoplax – Tesch 1918: 154 (part). — Sakai 1939: 555 [in key], 555; 1969: 269; 1976: 523 [in key] (part). — Chen 1984: 188; 1998: 266 (part). — Serène 1968: 89 [in list] (part). — Serène & Lohavanijaya 1973: 62, 63 [in key to species] (part). — Dai et al. 1986: 366 [in key to species] (part). — Guinot 1989: 273 (part). — Dai & Yang 1991: 394 [in key to species] (part). — Hsueh & Huang 2002: 116 [in key] (part). — Davie 2002: 193 (part). — Karasawa & Kato 2003b: 130 [in list], 140 [in list], 141 [in table] (part). — Poore 2004: 434 (part).

TYPE SPECIES. — Carcinoplax surugensis Rathbun, 1932 (by present designation; gender feminine).

SPECIES INCLUDED . — Pycnoplax bispinosa ( Rathbun, 1914) n. comb.; P.latifolia n. sp.; P.meridionalis ( Rathbun, 1923) n. comb.; P. surugensis ( Rathbun, 1932) n. comb.; P. victoriensis ( Rathbun, 1923) n. comb.

Most species are restricted to the Indo-West Pacific region; two species found in temperate areas contiguous to the Indo-West Pacific region.

ETYMOLOGY. — From pycno, Greek for “dense” or “thick”, in reference to the diagnostic thick G1, and plax, Greek for “plate” or “tablet”, which is derived from the generic name Carcinoplax (from karkinos, Greek for “crab”), to denote that four of the five species included in the new genus were formerly included in Carcinoplax sensu lato.

DESCRIPTION

Carapace ( Figs 13A, B ; 16A ; 17 ; Guinot 1989: pl. 12, fig. G, as Carcinoplax meridionalis , and pl. 12, fig. F, as C. victoriensis ) transversely quadrate, slightly wider than long, widest at junction of anterolateral, posterolateral borders; front lamellar, straight, not marked by median notch or projection. Notch between front, inner edge of supraorbital border (absent or barely discernible in P. bispinosa n. comb.); orbits narrow, not expanded distally; supraorbital borders slightly sinuous; suborbital borders rounded, with short, blunt inner tooth not visible dorsally; anterolateral borders convex; posterolateral borders long, arched. Dorsal surface of carapace smooth (2 slight horizontal ridges across carapace in P.victoriensis n. comb.; Guinot 1989: pl. 12, fig. F, as Carcinoplax victoriensis ) strongly convex, without clear indication of regions. Outer orbital angle with short, triangular tooth (absent in P. bispinosa n. comb., see Fig. 13B ); 2 anterolateral teeth on each side of carapace. Basal antennal article short, thick, distalmost (third) article reaches front. Eye peduncles ( Figs 13A, B ; 16A ; 17 ) short, much shorter than front (0.2 front width); cornea spherical, only slightly expanded distally. Anterior border of endostome well demarcated from buccal cavern, ridges faint but clearly defined. Third maxillipeds completely close the buccal cavern. 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, 7/8 interrupted medially, 6/7 complete ( Figs 14 ; 15 ; 18 ). Anterior end of sterno-abdominal cavity anterior to thoracic sternite 4. Cheliped fingers moderately slender, shorter than propodus (longer in P. latifolia n. sp.), tips darker in colour (except P. victoriensis n. comb.; Poore 2004: pl. 24, fig. b). Carpus with tooth on inner margin. Dorsal margins of meri, carpi, propodi of ambulatory legs (P2-P5) unarmed; dactyli slender, smooth, setose. Male abdomen with 6 freely-movable somites plus telson, relatively wide, somites 4-6 gradually decreasing in length from somite 3 (widest somite). Telson wider than long. Somite 3 covers space between P5 coxae, somite 2 slightly narrower than or as wide as somite 3 so that thoracic sternite 8 not visible or only leaving small portion visible (in P. bispinosa n. comb. and P. meridionalis n. comb.). G1 ( Fig. 16C ; Zarenkov 1972: fig. 6-2; Serène & Lohavanijaya 1973: figs 158-162; Chen 1984: figs 4-5, 4-6; Guinot 1989: fig. 30A, as Carcinoplax bispinosa ; Guinot 1969b: fig. 73; 1989: fig.31A; Chen 1984: figs 3-5, 3-6; Dai & Yang 1991: fig. 192-1, as C. surugensis ) stout, thick, proximally broad, diagonally oriented or straight with bent distal portion, with small spinules, pointed tip. G2 slender, slightly longer or noticeably longer than G1, typically dark brown, flagellum shorter or almost as long as proximal part (peduncle); tip pointed ( P. surugensis n. comb.), pointed with several spinules ( P. meridionalis n. comb.), slightly-expanded with 2 terminal spinules ( P. bispinosa n. comb., P. latifolia n. sp., P. victoriensis n. comb.). Penis arising from P5 coxa, moderate size; broad, soft proximal expansion. Female abdomen with 6 freely-movable somites, wide. Telson wider than long. Somite 3 covers space between P5 coxae, somite 2 narrower than somite 3 so that it leaves small portion of thoracic sternite 8 visible, or somite 2 as wide as somite 3 so that thoracic sternite 8 not visible. Vulva of full-grown, mature females ( Figs 15 ; 18 ) relatively small, not greatly enlarged, extending from suture 5/6 to suture 6/7, oblong or triangular vulvar cover (no evidence of a vulvar cover in small P. surugensis n. comb.; Fig. 14 ).

REMARKS

Serène & Vadon (1981: 127) suggested the inclusion of Carcinoplax bispinosa and C. surugensis in a separate genus based on their characteristic G1. Guinot (1969b: 526) commented on the differences between C. surugensis and other Carcinoplax species: wide sternum and abdomen, stout G1, and a G2 with a flagellum that is almost as long as the proximal part (peduncle) and ending in a pointed tip. It was nevertheless kept in Carcinoplax in her subsequent revision of the genus ( Guinot 1989). Carcinoplax surugensis was considered closer to C. meridionalis based on the shape of the carapace ( Guinot 1989: 303), even if the G1 of the latter, which proved to be similar, was not commented upon.Two species herein included in the new genus ( C. meridionalis and C. victoriensis ) were included by Guinot (1989: 314) in a list of eight “non-revised” species of Carcinoplax that are now, with only one exception, placed in other genera.

Pycnoplax n. gen. is similar in the general shape of its carapace to Carcinoplax . A case in point is the remarkable similarity between the carapaces of P. bispinosa n. comb. and C. tenuidentata n. sp. (see Remarks for P. bispinosa n. comb. below). The morphology of the G1 of Pycnoplax n. gen. (thick and stout, in contrast to slender and dorso-ventrally thin in Carcinoplax ), male abdomen (wider than in Carcinoplax ), and vulva (smaller and typically having a vulvar cover in Pycnoplax n. gen. in contrast to the greatly expanded vulva lacking a vulvar cover in Carcinoplax ), and a complete 6/7 thoracic suture (incomplete in Carcinoplax ), however, clearly separates the two genera. There are also slight differences in the basal antennal article (wider in Pycnoplax n. gen. than in Carcinoplax ) and the G2 (distal part relatively longer than proximal portion in Pycnoplax n. gen., much shorter in Carcinoplax , and the presence of proximal denticles on the distal part in Pycnoplax n. gen., absent in most species of Carcinoplax ).

Figures

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. 16. — Pycnoplax latifolia n. sp.,♂ holotype,cl 6.2 mm,cw 7.8 mm,Izu Is, Japan,Shinnyo-maru, cruise SY96,275-350 m (CBM-ZC 4624): 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. 17. — Pycnoplax latifolia n. sp.,♂ holotype,cl 6.2 mm,cw 7.8 mm,Izu Is, Japan,Shinnyo-maru, cruise SY96,275-350 m (CBM-ZC 4624).

FIG. 14. — Pycnoplax surugensis (Rathbun,1932) n. comb.,♀, cl 10.0 mm,cw 14.5 mm,South China Sea off Philippine Is, MUSORSTOM 2, stn CP 26, 299-320 m (MNHN-B 30056), thoracic sternum and vulva.

FIG. 15. — Pycnoplax bispinosa (Rathbun, 1914) n. comb., ♀, cl 11.2 mm, cw 13.4 mm, Tablas Strait, west of Mindoro, Philippine Is, MUSORSTOM 3, stn CP 120, 219-220 m (MNHN-B 30058), thoracic sternum, vulva, vulvar cover, and remains of sperm plug.

FIG. 18. — Pycnoplax victoriensis (Rathbun,1923) n. comb., ♀, cl 12.1 mm,cw 14.6 mm,off Victoria,Australia,stn SS01/00 187,500 m (NMV J52213), thoracic sternum, vulva, vulvar cover, and remains of sperm plug.