Cavoportunus Ng, 2010, new genus
Creators: name: Ng, Peter K. L.
Publisher: name: Zenodo
Year: 2010
Subjects: Biodiversity
Taxonomy
Animalia
Arthropoda
Malacostraca
Decapoda
Portunidae
Cavoportunus

description: 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.
description: Published as part of Ng, Peter K. L., 2010, A new genus of the family Portunidae (Crustacea: Decapoda: Brachyura) and the identity of Portunus (Cycloachelous) yoronensis Sakai, 1974, pp. 38-48 in Zootaxa 2677 on pages 39-40, DOI: 10.5281/zenodo.199230