Paragoneplax, 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 : 709-710

Genus Paragoneplax n. gen.

Goneplax – Komatsu & Takeda 2003: 1243 (part).

TYPE SPECIES. — Goneplax serenei Zarenkov, 1972 (by present designation and by monotypy; gender feminine).

SPECIES INCLUDED . — Paragoneplax serenei ( Zarenkov, 1972) n. comb.

The genus is restricted to the Indo-West Pacific region.

ETYMOLOGY. — From para, Greek for “beside” or “near”, and the generic name Goneplax , to indicate that although

the species included in the new genus superficially resembles Goneplax in the general shape of its carapace and its elongated eye peduncles, it actually belongs to a separate genus.

DESCRIPTION

Carapace ( Fig. 28C ) transversely rectangular, much wider than long; widest at conspicuous outer orbital teeth; front deflected ventrally, sinuous, with small median projection in larger individuals. Notch between front, inner edge of supraorbital border absent; orbits wide, greatly expanded distally; supraorbital borders conspicuously sinuous; suborbital borders sinuous, without inner tooth; nearly straight lateral borders. Dorsal surface of carapace with slight horizontal ridge, moderately convex, without clear indication of regions. Outer orbital angle with conspicuous, acute, tooth; no anterolateral teeth. Basal antennal article short, distalmost (third) article nearly reaches front. Eye peduncles ( Fig. 28C ) long, slightly shorter than front (0.8-0.9 front width); cornea strongly reniform, dorso-ventrally flattened, nearly divided into anterior and posterior portions. Anterior border of endostome well demarcated from buccal cavern, ridges faint but clearly defined. Third maxillipeds nearly 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. Anterior end of sterno-abdominal cavity anterior to thoracic sternite 4. Cheliped fingers ( Fig. 28C ) long, slender, shovel-like, curved, pollex higher than dactylus in large individuals, shorter than elongated propodus; dactylus light in colour, without dark portion; carpus with conspicuous tooth on inner margin. Dorsal margins of ambulatory leg (P2-P5) meri ( Fig. 28C ) with acute distal tooth; dactyli slender, with carina on each side, non-setose. Male abdomen ( Zarenkov 1972, fig. 7-2, as Geneplax [sic] serenei ; Chen 1998: fig. 12-5, as Goneplax serenei ) with 6 freely-movable somites plus telson, wide, somites 4-6 gradually decreasing in width from somite 3 (widest somite).Telson wide, clearly wider than long. Somite 3 covers space between P5 coxae, somite 2 narrower than somite 3; somites 1, 2 leave large portion of thoracic sternite 8 visible. G1 distally bent in fully grown males but straight in pre-adults ( Zarenkov 1972: fig. 7-2, as Geneplax [sic] serenei ; Chen 1998: fig. 12-6, 12-7, as G. serenei ). G2 ( Chen 1998: fig. 12-8, 12-9, as G. serenei ) slender, much shorter than G1, flagellum slightly curved, shorter than proximal part (peduncle), pointed tip. Penis arising from P5 coxa, long, soft; broad, soft proximal expansion. Female abdomen with 6 freely-movable somites, wide.Telson much wider than long. Somite 3 covers space between P5 coxae, somite 2 slightly narrower than somite 3; somites 1, 2 leave relatively large portion of thoracic sternite 8 visible. Vulva of mature females not greatly expanded, small, round, extending from 5/6 suture to median portion of thoracic sternite 6, vulvar cover absent, covered by soft membrane leaving anterior margin free.

REMARKS

Characteristic of Paragoneplax n. gen. is a G2 that is short, much shorter than the G1, in sharp contrast to the G2 of typical goneplacids, where the G2 is about the same length (or slightly longer or slightly shorter in some species) as the G1. The short size of the G2 is very puzzling. A short G2, considered the most derived character ( Guinot 1979: 243), is also present in Microgoneplax n. gen. (see description of the new genus below), as well as among most members of the families Euryplacidae Stimpson, 1871 , and Pseudoziidae Alcock, 1898 , taxa which were once included in the Goneplacidae sensu Balss 1957 . The hypothesis that both Paragoneplax n. gen. and Microgoneplax n. gen. should be grouped as a separate subfamily within the Goneplacidae sensu stricto is rejected as the species grouped in these two genera differ in some important characters such as the shape of the G1 (distally bent in Paragoneplax n. gen. but slender and straight in Microgoneplax n. gen.), shape of the male abdomen (unusually broad in Paragoneplax n. gen., more slender in Microgoneplax n. gen.), and the absence of a vulvar cover in Paragoneplax n. gen. (absent in Microgoneplax n. gen.). An alternate hypothesis is to consider both taxa as independent subfamilies, an arrangement that is rejected at this time. In any case, it seems prudent to speculate that a shorter G1 evolved independently among goneplacids.

Some additional characters of the new monotypic genus are discussed in the Remarks section for P. serenei n. comb. (see below). Other characters that separate Paragoneplax n. gen. from Goneplax sensu stricto and the five Indo-West Pacific genera that include species that were formerly included in Goneplax sensu lato are summarized in Table 4.

Figures

FIG. 28. — A, Goneplacoides marivenae (Komatsu & Takeda, 2003) n. comb., ♀, cl 7.6 mm, cw 11.6 mm, off southern coast of New Caledonia, SMIB 8, stn DW 177, 320-370 m (MNHN-B 29262); B, Neogoneplax renoculis (Rathbun, 1914) n. comb., ♂, cl 10.1 mm, cw 16.0 mm, South China Sea off Philippine Is, MUSORSTOM 3, stn CP 108, 188-195 m (MNHN-B 10334); C, Paragoneplax serenei (Zarenkov, 1972) n. comb., ♂, cl 8.6 mm, cw 14.9 mm, north of New Caledonia, BATHUS 1, stn CP 669 (MNHN-B 29327).