Microgoneplax, 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 : 724-725

Genus Microgoneplax n. gen.

Ommatocarcinus – Chen 1998: 285 (part).

TYPE SPECIES. — Microgoneplax caenis n. sp. (by present designation; gender feminine).

SPECIES INCLUDED . — Microgoneplax caenis n. sp.; M. cope n. sp.; M. elegans ( Chen, 1998) n. comb.; M. pelecis n. sp.; M. prion n. sp.

All species are restricted to the Indo-West Pacific region.

ETYMOLOGY. — From mikros, Greek for “small,” in reference to the small size of the G2 (much shorter than the G1) and the small overall size of the known species, and the generic name Goneplax , to indicate that although the species included in the new genus superficially resemble Goneplax in the general shape of their carapaces and elongated eye peduncles, they actually belong to a separate genus.

DESCRIPTION

Adults of small size (cw rarely more than 4.5 mm). Carapace ( Figs 41A ; 42 ; 43A ; 44A ; 45A ; 46 ; Chen 1998: fig. 14-1, as Ommatocarcinus elegans ) transversely rectangular, wider than long, relatively wider in larger individuals; widest at conspicuous outer orbital teeth; front slightly deflected ventrally, straight to slightly convex, not marked by median emargination (emargination described in M. elegans n. comb. [ Chen 1998: fig. 14-2]). Notch between front, inner edge of supraorbital border. Orbits wide, greatly expanded distally; supraorbital borders conspicuously sinuous, with tubercles; suborbital borders sinuous, with wide inner tooth not visible dorsally. Dorsal surface of carapace smooth, moderately convex, without clear indication of regions. Outer orbital angle with conspicuous, outwardly oriented, acute tooth; tooth medially placed on carapace. Slightly convex lateral borders without anterolateral teeth. Basal antennal article short, distalmost (third) article nearly reaches front. Eye peduncles long ( Figs 41A ; 42 ; 43A ; 44A ; 45A ; 46 ; Chen 1998: fig. 14-1, as Ommatocarcinus elegans ), slightly shorter or as long as front (0.7-1.0 front width); cornea elongated, spherical distal margin, not reniform (not conspicuously dorso-ventrally flattened, not clearly divided into anterior, posterior portions). Subhepatic, pterygostomial regions, with low, round tubercles. 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 tubercles of 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 ( Figs 42 ; 46 ; Chen 1998: figs 14-3, 14-4, as O. elegans ) long, slender, shovel-like, curved (conspicuously curved in large males), shorter than elongated propodus; inner (ventral) margin of propodus with large, round tubercles particularly in large males; carpus with blunt tooth on inner margin; merus typically with conspicuous tubercles on outer (dorsal) margin, long simple setae. Dorsal margins of ambulatory leg (P2-P5) meri ( Figs 42 ; 46 ) unarmed, dactyli slender, with carina on each side. Male abdomen ( Fig. 41B ) with 6 freely-movable somites plus telson, narrowly triangular (relatively wide in M. elegans n. comb.; see Chen 1998: fig. 14-6, as O. elegans ), somites 4-6 gradually decreasing in width from somite 3 (widest somite). Telson longer than wide. Somite 3 covers most space between P5 coxae, somite 2 slightly narrower than somite 3; somites 1, 2 leave large portion of thoracic sternite 8 visible. G1 ( Figs 41C ; 43B ; 44B ; 45B ; Chen 1998: fig. 14-7, as O. elegans ) long, slender, slightly broadened proximally, distal end varies among species. G2 ( Figs 41D ; 43C ; 44C ; 45C ; Chen 1998: fig. 14-8, as O. elegans ) short, less than half G1 length; slightly curved, thick flagellum about same length of proximal part (peduncle), much expanded tip. Penis arising from P5 coxa, moderate size, 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 small portion of thoracic sternite 8 visible. Vulva of mature females not expanded, ovoid, extending from 5/6 suture to median portion of thoracic sternite 6, vulvar cover present.

REMARKS

Microgoneplax n. gen. is being described as a new genus to accommodate the small-size species of Goneplax sensu lato where the G2 is much shorter than the G1, in contrast to Singhaplax where the G2 is longer or as long as the G1. Both genera share the basic morphology of the carapace and pereopods (see Remarks for Singhaplax above). There are, however, some additional differences. The male abdomen is wide (narrow in Singhaplax , except in one species), the front is straight (slightly convex in Singhaplax ), the suborbital tooth is conspicuous (short or obsolete in Singhaplax ), and the inner (ventral) margin of the P1 merus has conspicuous tubercles (smooth or with short granules in Singhaplax ). The outer orbital teeth are always medially placed on the carapace, whereas in some species of Singhaplax they are more anteriorly placed.

A short G2, the most derived character ( Guinot 1979: 243), is also present in Paragoneplax n. gen., but absent in the remaining members of the Goneplacidae sensu lato. The significance of this character in the suprageneric classification of the Goneplacidae is discussed in the description of Paragoneplax n. gen. (see above).

Members of the species of Microgoneplax n. gen. are also characterized by their small size. Males of different species can be distinguished because of their characteristic G1 but females are difficult to identify, particularly if they are pre-adults, do not have a characteristic vulva, or lack both chelipeds (P1). Females have been collected together with males of two different species, so co-occurrence of males and females is not always a reliable way to identify females.

Other characters that separate Microgoneplax 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. 41. — Microgoneplax caenis n. sp., ♂ holotype, cl 4.2 mm, cw 7.1 mm, between Panglao and Pamilacan islands, Philippine Is, PANGLAO 2004, stn T27 (NMCR 27014):A, dorsal surface of the carapace; B, abdomen;C, right G1, ventral view; D, right G2,ventral view. Scale bars: A, 5 mm; B, 2 mm; C, D, 1 mm.

FIG. 42. — Microgoneplax caenis n. sp., ♂ holotype, cl 4.2 mm, cw 7.1 mm, between Panglao and Pamilacan islands, Philippine Is, PANGLAO 2004, stn T27 (NMCR 27014).

FIG. 43. — Microgoneplax cope n.sp., ♂ holotype,cl 4.4 mm,cw 8.4 mm,Futuna I., South Pacific,MUSORSTOM 7, stn DW 513 (MNHN-B 30063): A, dorsal surface of the carapace; B, left G1, ventral view; C, left G2, ventral view. Scale bars: A, 5 mm; B, C, 1 mm.

FIG. 44. — Microgoneplax pelecis n. sp.,♂ holotype,cl 3.9 mm,cw 6.7 mm,Kai Is, Indonesia,KARUBAR,stn DW 29 (MNHN-B 30065): A, dorsal surface of the carapace; B, left G1, ventral view; C, left G2, ventral view. Scale bars: A, 5 mm; B, C, 1 mm.

FIG. 45. — Microgoneplax prion n. sp., ♂ holotype, cl 3.9 mm, cw 7.3 mm, Chesterfield Is, MUSORSTOM 5, stn DW 280 (MNHN-B 29318): A, dorsal surface of the carapace; B, left G1, ventral view; C, left G2, ventral view. Scale bars: A, 5 mm; B, C, 1 mm.

FIG. 46. — Microgoneplax prion n. sp., ♂ holotype, cl 3.9 mm, cw 7.3 mm, Chesterfield Is, MUSORSTOM 5, stn DW 280 (MNHN-B 29318) (photo by P. Laboute, IRD, Nouméa).