Cavoportunus, Ng, Peter K. L., 2010

Ng, Peter K. L., 2010, A new genus of the family Portunidae (Crustacea: Decapoda: Brachyura) and the identity of Portunus (Cycloachelous) yoronensis Sakai, 1974, Zootaxa 2677, pp. 38-48 : 39-40

Cavoportunus new genus

Type species. Neptunus (Achelous) dubia Laurie, 1906 , by present designation.

Diagnosis. Carapace hexagonal in shape, width approximately 1.3 times length, dorsal surfaces glabrous; frontal margin slightly upturned; surface microscopically granular with distinct regions; metagastric ridge distinctly visible, other ridges indistinct, dorsal surface with numerous small granules ( Figs. 1 , 2 A, 4A). Front with 4 teeth, slightly projecting beyond tip of internal supraorbital angle ( Figs. 1 , 2 A, 4A). Orbit relatively large, with moderate dorsal inclination, inner supraorbital margin rounded, upper border of orbit with single fissure ( Figs. 1 , 2 A, 4A). Infraorbital margin straight, with forward-directed tooth ( Fig. 2 ). Anterolateral margin with 9 teeth, first tooth largest, second to ninth teeth smaller, subequal in size ( Figs. 1 , 2 A, 4A). Posterolateral junction of carapace rounded ( Figs. 1 , 2 A, 4A). Basal antennal article with lobe-like process ( Fig. 2 C). Merus of third maxilliped produced anterolaterally ( Figs. 2 C, 3C). Cheliped length approximately 1.8 times width of carapace, manus slightly less massive than merus, fingers relatively long, slender ( Figs. 1 , 2 A, B, 3A, B). Adult male with 2 prominent deep depressions on sternite 8 inside sterno-abdominal cavity, anterior being larger, in which G1 sits ( Figs. 3 D, 4C). G1 very short, relatively stout, S-shaped; basal part relatively slender, subdistal part prominently dilated, lobiform; distal part with distinct folds on tip ( Figs. 3 E, 4D); G2 elongate, tapering, about four-fifths length of G1 ( Fig. 4 E). Penis coxal, long, slender, proximally lodged between 2 raised processes of sternite 8 ( Fig. 3 D). Vulvae mostly surrounded by thick, whitish, crescent-shaped rim; salient, short sternal cover on outer margin; separate, small, round operculum ( Fig. 3 G).

Etymology. Cavoportunus is a combination of the Latin cavo, for “hollow”, alluding to the depressions for the G1 on the male sterno-abdominal cavity, and the generic name Portunus . The gender is masculine.

On the composition of Achelous De Haan, 1833 , and Cycloachelous Ward, 1942 . According to Ng et al. (2008: 151), the subgenus Achelous De Haan, 1833 , of Portunus Weber, 1795 , comprises 22 species and subspecies. Portunus dubius ( Laurie, 1906) has been retained in the subgenus Achelous since its original description by Laurie. Alcock (1899: 30) was the first to diagnose the subgenus in detail: “Carapace suborbicular or not very broad, flat, the postero-lateral junctions rounded. Front slightly projecting beyond the internal supra-orbital angles: the last spine of the antero-lateral border either hardly larger or actually smaller than any of the others. Orbits of moderate size and with a moderate dorsal inclination. Antero-external angle of basal antennal articles forming a lobe-like process. Epistome hardly produced in the middle line: anteroexternal angle of merus of external maxillipeds strongly produed in a lateral direction. Hand hardly less massive than the arm.” Rathbun (1930: 62) diagnosed it more simply: “Carapace narrow, the antero-lateral margin being the arc of a circle with short radius, whose center is near center of cardiac region. Last spine of antero-lateral margin usually not much if any larger than the others.” Some authors (e.g. Garth & Stephenson 1966; Stephenson & Rees 1967), however, have expressed doubt about the validity of Achelous and have refrained from using the subgenus, treating it merely as a synonym of Portunus Weber, 1795 s . str. (e.g., Stephenson 1972a, b). Ward (1942) independently established a new genus, Cycloachelous , with Lupa granulatus H. Milne Edwards, 1834 , as the type species. This genus was not recognized by most workers, who have treated Cycloachelous species as part of Portunus (e.g. Stephenson 1972a, b; Stephenson & Rees 1967). Davie (2002), however, following comments by Stephenson & Campbell (1959) on the features of Portunus granulatus , decided to recognise Cycloachelous as a valid subgenus of Portunus , but only for this P. granulatus . Ng et al. (2008), however, continued to treat Cycloachelous as a synonym of Achelous .

The subgenus Achelous was recently redefined mainly on the basis of molecular data ( Mantelatto et al. 2009) and the subgenus was elevated to the status of a full genus to include 10 American species, six of which were originally in the subgenus Achelous De Haan, 1833 , sensu Ng et al. (2008) , including the type species P.

spinimanus Latreille, 1819 , with one species transferred from Crosnius Stimpson, 1860, and three from Portunus (Portunus) Weber, 1795 . The American Portunus (Achelous) floridanus Rathbun, 1930 , was allied with three species in the subgenus Portunus (Portunus) : P. (P.) anceps ( Saussure, 1858) , P. (P.) hastatus ( Linnaeus, 1767) , and P. (P.) ventralis ( A. Milne-Edwards, 1879) , but their generic status was deemed uncertain. Mantelatto et al. (2009) did not treat the other 16 species and subspecies of Achelous , many of which are Indo-West Pacific in distribution. The generic placements of seven other American species previously placed in Portunus (Achelous) (in their original generic combination): Portunus (Achelous) angustus Rathbun, 1898 , Achelous brevimanus Faxon, 1895 , Portunus (Achelous) guaymasensis Garth & Stephenson, 1966 , Neptunus (Hellenus) iridescens Rathbun, 1894 , Portunus (Achelous) isolamargaritensis Türkay, 1968 , Portunus (Achelous) stanfordi Rathbun, 1902 , and Achelous tuberculatus Stimpson, 1860 , were not discussed. These are here very tentatively retained in Achelous sensu lato in the absence of any alternate classification. Neither did Mantelatto et al. (2009) discuss the generic and/or subgeneric assignments of the nine Indo-West Pacific taxa discussed: Neptunus (Achelous) dubia Laurie, 1906 , Achelous elongatus A. Milne-Edwards, 1861 , Lupa granulatus H. Milne Edwards, 1834 , Achelous granulatus unispinosus Miers, 1884 , Neptunus octodentatus Gordon, 1938 , Achelous orbicularis Richters, 1880 , Portunus (Achelous) orbitosinus Rathbun, 1911 , Portunus (Achelous) suborbicularis Stephenson, 1975 , and Portunus (Cycloachelous) yoronensis Sakai, 1974 . On the basis of their similar carapace shapes and features (rounded carapaces with low anterolateral teeth all subequal in size), all the Indo-West Pacific species can be easily referred to Cycloachelous Ward, 1942 . Davie (2002) only recognized Lupa granulatus in Cycoachelous, but kept the related Portunus orbitosinus in the subgenus Achelous . However, it is more parsimonious if both are placed together in Cycloachelous . The only two “ Cycloachelous ” species with similar carapace features but with very different male thoracic sternums and gonopods that could be considered to belong to Cycloachelous are Neptunus (Achelous) dubia and Portunus (Cycloachelous) yoronensis , here regarded as subjective synonyms (see below).

Remarks. Neptunus (Achelous) dubius Laurie, 1906 , differs from the type species of Achelous , Portunus spinimanus , in a number of characters: a) the carapace is longer than wide, width about 1.3 times length ( Figs. 1 , 2 A, 4A) (broader carapace, width 1.6–1.8 times length in P. spinimanus ); b) the presence of only a few indistinct ridges on the carapace ( Figs. 1 , 2 A, 4A) (distinct granular ridges on the carapace of P. spinimanus ); c) the infra-orbital margin is straight ( Fig. 2 C) (curved in P. spinimanus ); d) the upper border of the orbit has a single fissure ( Figs. 1 , 2 A, 4A) (two fissures in P. spinimanus ); e) the anterior margin of the male third abdominal somite is sinuous ( Figs. 2 B, 4B) (straight in P. spinimanus ); f) the male sixth abdominal somite is relatively broader and shorter, with a length to width ratio of 0.77 maximum ( Figs. 2 B, 4B) (0.98 in P. spinimanus ); g) the presence of two distinct depressions lateral to the sternal medial groove on the male sternum to accommodate G1 ( Figs. 3 D, 4C) (absence of such depressions in P. spinimanus ); and h) the subdistal part of the G1 is swollen and bilobed ( Figs. 3 E, 4D) (slender and elongated tip of the G 1 in P. spinimanus ).

On the basis of the carapace shape and form of the chelipeds, Neptunus (Achelous) dubia is close to Cycloachelous . However, it differs from the type species of this taxon, Lupa granulatus H. Milne Edwards, 1834 , markedly in the form of the male thoracic sternum and structure of the G1 ( Fig. 5 D). In Neptunus dubia , thoracic sternite 8 is deeply excavated to form two deep depressions (anterior more prominent) to accommodate the base and swollen subdistal part of the G1 ( Figs. 3 D, E, 4C, D). In the species of Cycloachelous , the male thoracic is normal, with sternite 8 gently concave and without any obvious depressions; and the G1 is also not prominently swollen, the distal parts being elongated and slender ( Fig. 5B , D). For these reasons, a new genus, here named Cavoportunus , is established for Neptunus dubia Laurie, 1906 .

Comparative material. Portunus (Achelous) spinimanus ( Latreille, 1819) : 1 male (57.1 × 31.5 mm), 1 female (60.0 mm × 33.5 mm) ( ZRC 2008.0150), Brazil, Cabiunas, coll. UFRJ, 25 April 1993. Cycloachelous granulatus (H. Milne Edwards, 1834) ; 3 males (22 × 15.4 mm, 21.5 × 14.2 mm, 19.3 × 13.5 mm), 1 female (16.6 × 11.5 mm) ( ZRC 2000.0653), Guam, Pago Bay, outside University of Guam Marine Laboratory, coll. P. K. L. Ng & C. H. Wang, 15–18 April 2000. Cycloachelous orbicularis ( Richters, 1880) ; 1 male (18.7 × 14.23mm) (NHMLAC JM0131), Northwest Hawaiian Is., French Frigate Shoals, 23.709°N 166.3ºW to 23.7ºN 166.298ºW, 12–21 m, submerged banks, dredge, station FFS 0 100, DBT3, coll. R. Moffitt & R. Brainard, 17 October 2006.

Figures

FIGURE 1. Live colour. Cavoportunus dubius (Laurie, 1906). Female (13.0 × 10.2 mm) (NSMT-KY- 08 - 15), dorsal overall view. Scales = 1.0 mm. (Photograph: H. Komatsu).

FIGURE 2. Cavoportunus dubius (Laurie, 1906). A, lectotype male (10.2 × 8.1 mm) (NHM 1907.5.22.320); B, C, male (18.5 × 14.6 mm) (ZRC 2001.0627). A, overall dorsal view; B, ventral view of thoracic sternum and abdomen; C, frontal view of carapace.

FIGURE 3. Cavoportunus dubius (Laurie, 1906). A-C, parts of paralectotype, male (NHM 1907.5.22.320). A, B, left cheliped; C, right third maxiliped; D, E, male (18.5 × 14.6 mm) (ZRC 2001.0627). D, thoracic sternum with intact right G 1; E, different views of G 1; F, G, female (18.5 × 14.3 mm (ZRC 2001.0627). F, abdomen; G, thoracic sternum; H, juv. male (9.7 × 7.3 mm) (WMNH-Na-Cr 0539) thoracic sternum. Abbreviations: p = penis; pb = press button. Scales = 1.0 mm.

FIGURE 4. Cavoportunus dubius (Laurie, 1906). A, lectotype male, (10.2 × 8.1 mm) (NHM 1907.5.22.320); B-F. male, (18.5 × 14.6 mm) (ZRC 2001.0627). A, carapace; B, male abdomen; C, male thoracic sternum with intact right G 1; D, different views of left G 1; E, right G 2; F, distal part of right G 2. Scales: A-E = 1.0 mm, F = 0.2 mm.

FIGURE 5. A, B, Cycloachelous orbicularis (Richters, 1880), male (18.7 × 14.23 mm) (NHMLAC JM 0131) (Photographs: J. C. E. Mendoza); C, D, Cycloachelous granulatus (H. Milne Edwards, 1834), male, (22 × 15.4 mm) (ZRC 2000.0653). A, C, dorsal overall views; B, D, anterior male thoracic sternums showing abdominal cavities and gonopods. Scales = 1.0 mm.