Cavoportunus
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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
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, 2
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A, 4A). Front with 4 teeth, slightly projecting beyond tip of internal supraorbital angle ( Figs. 1
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, 2
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A, 4A). Orbit relatively large, with moderate dorsal inclination, inner supraorbital margin rounded, upper border of orbit with single fissure ( Figs. 1
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, 2
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A, 4A). Infraorbital margin straight, with forward-directed tooth ( Fig. 2
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). Anterolateral margin with 9 teeth, first tooth largest, second to ninth teeth smaller, subequal in size ( Figs. 1
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, 2
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A, 4A). Posterolateral junction of carapace rounded ( Figs. 1
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, 2
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A, 4A). Basal antennal article with lobe-like process ( Fig. 2
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C). Merus of third maxilliped produced anterolaterally ( Figs. 2
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C, 3C). Cheliped length approximately 1.8 times width of carapace, manus slightly less massive than merus, fingers relatively long, slender ( Figs. 1
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, 2
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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
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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
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E, 4D); G2 elongate, tapering, about four-fifths length of G1 ( Fig. 4
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E). Penis coxal, long, slender, proximally lodged between 2 raised processes of sternite 8 ( Fig. 3
View FIGURE 3
D). Vulvae mostly surrounded by thick, whitish, crescent-shaped rim; salient, short sternal cover on outer margin; separate, small, round operculum ( Fig. 3
View FIGURE 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
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, with one species transferred from Crosnius Stimpson, 1860, and three from
Portunus (Portunus) Weber, 1795
. The American
Portunus (Achelous) floridanus Rathbun, 1930
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, was allied with three species in the subgenus
Portunus (Portunus)
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:
P. (P.) anceps ( Saussure, 1858)
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,
P. (P.) hastatus ( Linnaeus, 1767)
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, and
P. (P.) ventralis ( A. Milne-Edwards, 1879)
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, but their generic status was deemed uncertain. Mantelatto et al. (2009) did not treat the other 16 species and subspecies of
Achelous
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, many of which are Indo-West Pacific in distribution. The generic placements of seven other American species previously placed in
Portunus (Achelous)
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(in their original generic combination):
Portunus (Achelous) angustus Rathbun, 1898
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,
Achelous brevimanus Faxon, 1895
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,
Portunus (Achelous) guaymasensis Garth & Stephenson, 1966
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,
Neptunus (Hellenus) iridescens Rathbun, 1894
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,
Portunus (Achelous) isolamargaritensis Türkay, 1968
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,
Portunus (Achelous) stanfordi Rathbun, 1902
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, and
Achelous tuberculatus Stimpson, 1860
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, 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
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,
Achelous elongatus A. Milne-Edwards, 1861
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,
Lupa granulatus H. Milne Edwards, 1834
,
Achelous granulatus unispinosus Miers, 1884
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,
Neptunus octodentatus Gordon, 1938
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,
Achelous orbicularis Richters, 1880
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,
Portunus (Achelous) orbitosinus Rathbun, 1911
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,
Portunus (Achelous) suborbicularis Stephenson, 1975
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, and
Portunus (Cycloachelous) yoronensis Sakai, 1974
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. 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
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. Davie (2002) only recognized
Lupa granulatus
in Cycoachelous, but kept the related
Portunus orbitosinus
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in the subgenus
Achelous
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. However, it is more parsimonious if both are placed together in
Cycloachelous
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. The only two “
Cycloachelous
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” species with similar carapace features but with very different male thoracic sternums and gonopods that could be considered to belong to
Cycloachelous
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are
Neptunus (Achelous) dubia
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and
Portunus (Cycloachelous) yoronensis
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, 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
View FIGURE 1
, 2
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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
View FIGURE 1
, 2
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A, 4A) (distinct granular ridges on the carapace of
P. spinimanus
); c) the infra-orbital margin is straight ( Fig. 2
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C) (curved in
P. spinimanus
); d) the upper border of the orbit has a single fissure ( Figs. 1
View FIGURE 1
, 2
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A, 4A) (two fissures in
P. spinimanus
); e) the anterior margin of the male third abdominal somite is sinuous ( Figs. 2
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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
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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
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D, 4C) (absence of such depressions in
P. spinimanus
); and h) the subdistal part of the G1 is swollen and bilobed ( Figs. 3
View FIGURE 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
View FIGURE 5. A, B
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
View FIGURE 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
View FIGURE 5. A, B
, 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.