Exopheticus, 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 : 745-747

Genus Exopheticus n. gen.

Psopheticus – Alcock 1900: 292 [in list], 298 [in key], 308 (part). — Tesch 1918: 160 (part). — Sakai 1939: 555 [in key], 558 (part); 1976: 523 [in key], 529 (part). — Balss 1957: 1656 (part). — Serène 1968: 90 [in list] (part). — Guinot 1969b: 528 (part); 1971: 1081 (part); 1990: 333 (part). — Hsueh & Huang 2002: 116 [in key] (part). — Poore 2004: 438 (part).

TYPE SPECIES. — Psopheticus hughi ( Rathbun, 1914) (by present designation; gender masculine).

SPECIES INCLUDED . — Exopheticus hughi ( Rathbun, 1914) n. comb.; E. insignis ( Alcock, 1900) n. comb.

All species are restricted to the Indo-West Pacific region. ETYMOLOGY. — From exo, Greek for “out of ”, and pheticus, derived from the generic name Psopheticus (from psophos, Greek for “sound”), to denote that the type species of the new genus was formerly included in Psopheticus Wood-Mason, 1892 .

DESCRIPTION

Carapace ( Fig. 48A ; Guinot 1990: figs 10-12, as Psopheticus insignis ; fig. 17, as P. hughi ; Chen 1998: fig. 7-1, as P. insignis ) subcircular; front straight, often slightly concave, not marked by median notch or projection. Notch between front, inner edge of supraorbital border absent (distinct in small specimens); orbits wide distally to accommodate eyes; eyes reniform, dorso-ventrally flattened, cornea greatly expanded distally, nearly divided into anterior, posterior portions. Supraorbital borders conspicuously sinuous; suborbital borders rounded, with short, blunt inner tooth (absent in small specimens) not visible dorsally; anterolateral borders arched so that fronto-orbital border is narrower than maximum width of carapace at junction of anterolateral, posterolateral borders. Dorsal surface of carapace smooth, slightly convex, without clear indication of regions. Outer orbital teeth strongly projecting, flattened, triangular; anterolateral tooth on each side of carapace (obsolete in large E. insignis n. comb.). Basal antennal article short, slender, distalmost (third) article reaches front. Eye peduncles ( Fig. 48A ; Guinot 1990: figs 10-12, as P. insignis ; fig. 17, as P. hughi ; Chen 1998: fig. 7-1, as P. insignis ) relatively short to moderately long (0.2-0.5 front width; Fig. 48A ; Guinot 1990: figs 10-12, as P. insignis ; fig. 17, as P. hughi ; Chen 1998: fig. 7-1, as P. insignis ), shorter than front; eyes reniform, dorso-ventrally flattened, cornea greatly expanded distally. Anterior border of endostome well demarcated from buccal cavern, ridges faint but clearly defined. Third maxillipeds completely close the buccal cavern. Stridulating mechanism of subocular, elliptical pterygostomial crest rubbing against proximal portion of cheliped (P1) merus. Thoracic sternum wide. Median sulcus on thoracic sternite 4 absent; sutures 4/5, 5/6, 7/8 interrupted medially, 6/7 complete ( Figs 49 ; 50 ; Guinot 1990: fig. 16, as P. insignis ). Anterior end of sterno-abdominal cavity anterior to thoracic sternite 4. Cheliped fingers ( Guinot 1990: figs 10-12, as P. insignis , figs 17, 18, as P. hughi ; Chen 1998: fig. 7- 2, as P. insignis ) slender, shorter than propodus, dark in colour (light colour in E. hughi n. comb.); carpus with tooth on inner margin; merus becomes greatly elongated with size ( Guinot 1990: figs 11, 12) in E. insignis n. comb. Dorsal margin of merus of P2 ( Guinot 1990: fig. 17, as P. hughi ) with subdistal tooth (may be obsolete in E. insignis n. comb.); dorsal margins of meri of P3-P5 ( Guinot 1990: figs 10-12, as P. insignis , fig. 17, as P. hughi ) with subdistal tooth (may be obsolete in large specimens); dorsal margins of carpi, propodi of ambulatory legs (P2-P5) smooth; dactyli slender, smooth (carinated in small specimens), setose. Male abdomen ( Fig. 48B ; Chen 1998: fig. 7-5, as P. insignis ; Hsueh & Huang 2002: fig. 13H, as P. hughi , fig. 14E, as P. insignis ) 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 much longer than somite 3 so that somites 1, 2 leave large, subquadrate to rectangular portion of thoracic sternite 8 visible in E. insignis n. comb. ( Hsueh & Huang 2002: fig. 14C, as P. insignis ; small triangular portion in E. hughi n. comb.); somite 1 mostly covered by carapace. G1 ( Fig. 48C ; Guinot 1990: figs 13, 14; Chen 1998: fig. 7-6, as P. insignis ; Hsueh & Huang 2002: fig.13D, as P. hughi , fig. 14F, as P. insignis ) long, slender, sinuous, only slightly broadened proximally, truncated tip. G2 ( Fig. 48D ; Guinot 1990: fig. 15; Chen 1998: fig. 7-7, as P. insignis ) slender, nearly equal or slightly longer than G1, flagellum slightly shorter than basal part, with basal spinules, slightly-expanded tip. Penis arising from P5 coxa, long, soft; wide, soft proximal expansion. Female abdomen with 6 freely-movable somites, wide. Telson subovate ( Hsueh & Huang 2002: fig. 13I, as P. insignis ). Somite 3 covers space between P5 coxae, somites 1, 2 slightly narrower than or as wide as somite 3, only small portion or no portion at all of thoracic sternite 8 visible. Vulva of mature females ( Figs 49 ; 50 ) round, extending to sutures 5/6 and 6/7 of thoracic sternite 6, covered by soft membrane; vulvar cover absent.

REMARKS

Exopheticus n. gen. includes two species previously included in Psopheticus , as P. hughi Rathbun, 1914 , and P. insignis Alcock, 1900 . According to Alcock (1900: 311) Psopheticus insignis “closely connects” Psopheticus and Carcinoplax H. Milne Edwards, 1852 . Serène & Vadon (1981: 127) had also commented on the sharp differences (“totalement différent”) between the G1 of E. insignis n. comb. (as Psopheticus insignis Alcock, 1900 ), similar to that of Carcinoplax , and the G1 of its congener, P. stridulans . They also commented on the similarities between the carapace and chelipeds (P1) of E. insignis n. comb. and those of some species of Carcinoplax , particularly C. longimana (de Haan, 1833) . Guinot (1969b: 528) remarked on the need of establishing a diagnosis for Psopheticus in order to determine if P. insignis and P. hughi belonged to the same genus as P. stridulans . Unfortunately, her revision of Psopheticus ( Guinot 1990) did not include a diagnosis. Such a diagnosis would have undoubtedly demonstrated the peculiarities of P. insignis and P. hughi on one hand and P. stridulans (and three other species of Psopheticus sensu lato) on the other, with their subsequent separation as different genera.

Exopheticus n. gen. is characterized by a slender G1 ( Fig. 48C ; Guinot 1990: fig. 13; Chen 1998: fig. 7-6, as P. insignis ) in contrast to a stout G1 with a broad, nearly triangular proximal part in Psopheticus ( Zarenkov 1972: fig. 6-5; Guinot & Richer de Forges 1981b: fig. F; Guinot 1990: figs 44, 47, 50, 52). The vulva ( Figs 49 ; 50 ) is large, extending between sutures 5/6 and 6/7 of thoracic sternite 6, with smooth margins lacking a vulvar cover, and covered by a soft membrane. This condition is in contrast to Psopheticus , where the vulva is much smaller, extending only along the margin of suture 5/6, in a large depression on thoracic sternite 5, and bordered on the posterior edge by a hook-like vulvar cover (barely visible in Fig. 47 ). The carapace is subcircular in Exopheticus n. gen. (subquadrate in Psopheticus ), the dorsal margins of P3-P5 have only one distal tooth ( Chen 1998: fig. 7-4, as P. insignis ) but several teeth in Psopheticus , the first and second somites of the male abdomen leave a large subquadrate portion of thoracic sternite 8 visible (only a small triangular portion remains visible in Psopheticus and in E. hughi n. comb.; Guinot & Richer de Forges 1981b: fig. 12D; Guinot 1990: fig. 24, as P. insignis ), and the inner margin of the suborbital border is only marked by a short tooth not visible dorsally in larger individuals (conspicuous tooth in Psopheticus ). The stridulating mechanism of Exopheticus n. gen. appears to involve only the rubbing of the cheliped merus against the subhepatic surface of the carapace ( Guinot 1990: figs 58-60, as P. insignis and P. hughi ) whereas teeth in the merus appear to be involved in Psopheticus ( Guinot 1990: figs 55-57).

In comparing her new species, P. hughi , with P. stridulans and P. insignis (= E. insignis n. comb.), Rathbun (1914: 145) mentioned that in the latter two species the first and second somites of the male abdomen do not cover the thoracic sternites as in the holotype of P. hughi (USNM 46180), the only specimen she apparently examined. Practically all the male specimens of E. hughi n. comb. that were examined during this study, however, showed that the first and second somites leave a small triangular area of the thoracic sternite 8 exposed as in the species of Psopheticus and unlike E. insignis n. comb., where a much larger, square to rectangular portion is left exposed. In some small specimens of E. hughi n. comb., however, an even smaller portion of the sternum is left exposed. The drawing of the posterior portion of the abdomen of E. hughi n. comb. in Hsueh & Huang (2002: fig. 13C, as Psopheticus hughi ) is unfortunately not clear as to which portions of the thoracic sternum are left exposed.

In contrast to Psopheticus , Exopheticus n. gen. shares with Carcinoplax the structure of its G1, G2, and vulva. Exopheticus n. gen. is nevertheless distinguished from Carcinoplax in that its thoracic suture 6/7 is complete (interrupted medially in Carcinoplax ), the first and second somites of the male abdomen leave a large subquadrate portion of thoracic sternite 8 visible (only a small portion of the thoracic sternite is visible in Carcinoplax ), the orbits are wide distally to accommodate the reniform eyes (orbits not expanded and the cornea of the eyes are rounded in Carcinoplax ), the supraorbital borders are sinuous (only slightly curved in Carcinoplax ), there is an obvious, specialized stridulating mechanism (absent in Carcinoplax ), and the dorsal margin of the carpi and propodi of the P3-P5 have a subdistal tooth (absent in Carcinoplax , except C. spinosissima Rathbun, 1914 ).

Figures

FIG. 48. — Exopheticus insignis (Alcock, 1900) n. comb., ♂ holotype, cl 22.4 mm, cw 30.9 mm, Bligh Water, Fiji, MUSORSTOM 10, stn CP 1320, 290-300 m (MNHN-B 29369): A, dorsal surface of the carapace; B, abdomen; C, left G1, dorsal view; D, left G2, ventral view. Scale bars: A, B, 5 mm; C, D, 1 mm.

FIG. 49. — Exopheticus insignis (Alcock, 1900) n. comb.,♀, cl 22.7 mm,cw 31.5 mm,South China Sea off Philippine Is, MUSORSTOM 2, stn CP 20, 192-185 m (MNHN-B 30059), thoracic sternum and vulva.

FIG. 50. — Exopheticus hughi (Rathbun, 1914) n. comb., ♀, cl 30.5 mm, cw 41.4 mm, off northeastern Taiwan, TAIWAN 2001, stn CP 102, 326-331 m (MNHN-B 29668), thoracic sternum and vulva.

FIG. 47. — Psopheticus stridulans Wood-Mason, 1892, ♀, cl 22.8 mm, cw 28.1 mm, Tanimbar Is, Indonesia, KARUBAR, stn CP 77, 352-346 m (MNHN-B 30057), thoracic sternum and vulva, vulvar cover, and remains of sperm plug.