Pachygrapsus fakaravensis Rathbun, 1907

Poupin, Joseph, Davie, Peter J. F. & Cexus, Jean-Christophe, 2005, A revision of the genus Pachygrapsus Randall, 1840 (Crustacea: Decapoda: Brachyura, Grapsidae), with special reference to the Southwest Pacific species, Zootaxa 1015 (1), pp. 1-66 : 12-15

Pachygrapsus fakaravensis Rathbun, 1907 ( Figures 3a–f ; 14a ; 15a )

Pachygrapsus fakaravensis Rathbun, 1907: 29 , pl. 5, fig. 1, pl. 9, fig. 6, 6a [type locality: Fakarava Atoll, Tuamotu Archip., French Polynesia]. — Tesch, 1918: 76 (Key). — Sakai, 1976: 636, pl. 218, fig. 3 ( Japan). — Hwang & Yu, 1980: 153, pl. 11­2 (Taiwan). — Monteforte, 1984: 172, annex I, tab. a (Tuamotu Archip.). — Poupin, 1994: 62, fig. 58, pl. 7e (Tuamotu Archip.). — Davie, 1998a: 63 (Hawaiian Is.). — DeFelice et al., 2001: 45 (Hawaiian Is.). — Ng et al., 2001: 40, fig. 8e (Hawaiian Is., Taiwan; references).

Type material Male holotype, 18.0 x 19.4 mm ( USNM 32844 ) .

Material Examined

French Polynesia. Tuamotu Archip.: Fakarava Atoll, outer reef, coll. USS Albatross , 12 October 1899, M holotype 18.0 x 19.5 mm ( USNM 32844 ); Taiaro Atoll, outer reef, low tide at night, on big coral rocks, Taiaro Expedition, coll. J. Poupin, 12–20 February 1994, 1 ov. F 15.0 x 16.5 mm ( MNHN B25782) . — Hawaiian I.: Milolii , intertidal on rocks at night, coll. G. Paulay, 31 October 1997, 1 ov. F. 12.9 x 15.1 mm ( UF 2255 ; erroneously labelled P. plicatus ) .

Diagnosis

Carapace subquadrate; lateral margins almost parallel with no tooth behind exorbital angle ( Fig. 3a ). Dorsal surface weakly convex with strong transverse striae with setae. Front 0.5 times carapace width at exorbital angles; anterior margin sinuous ( Fig. 3b ). Infraorbital margin dentate along entire length, separated from outer orbital tooth by deep notch ( Fig. 14a ).

Chelipeds equal. Merus with deep transverse striae with setae; dorsal, anterior margins with few mobile spines, inner ventrodistal lobe with 3–4 teeth. Carpus with few granules, short striae with setae; inner spine stout, blunt. Outer face of chela with several longitudinal striae formed by rounded tubercles with setae on lower half; upper half with rounded granules surrounded by setae ( Fig. 3c ). Tips of fingers spoon­like, glabrous.

Meri of ambulatory legs with deep transverse to oblique ridges with setae; lower margin of P5 meri without sub­median tubercle ( Fig. 3d ). Carpi, propodi with two longitudinal striae with setae. Dactyli ending in strong corneous claw; dorsal, ventral margins with rows of strong, moveable spines.

Male with numerous short setiferous striae on abdominal tergites, thoracic sternites; sixth somite of abdomen plus telson triangular ( Fig. 3e ). Female with several short setiferous striae on abdominal tergites ( Fig. 3f ). G1 with long, horn­like process with minute spinule medially ( Fig. 15a ).

Colour: overall brown to dark brown with violet hues and paler areas on ambulatory legs.

Measurements: carapace of specimens examined ranging from 12.9 x 15.1 to 15.0 x 16.5 mm.

Distribution

West and Central Pacific. Japan; Taiwan, Hawaiian Is., French Polynesia (Tuamotu Archip.: Fakarava, Makatea, Mataiva, Taiaro, Takapoto).

Habitat Collected at upper level of reefs at night; uncommon. Remarks

Pachygrapsus fakaravensis is uncommon, rarely reported in the literature. It is morphologically close to the Indo­West Pacific P. plicatus (H. Milne Edwards, 1837) , which has similar coarse striations on the carapace and the same longitudinal striae on the outer face of the chelae. The two species have been collected together in French Polynesia. They can be separated by the shape of the lateral carapace margins (subparallel in P. fakaravensis , posteriorly convergent in P. plicatus ), the presence of setae on the longitudinal striae of the outer face of the chelae of P. fakaravensis , and by the abdominal tergites having short striae in P. fakaravensis but being smooth in P. plicatus . The shape of the G1, figured here for the first time for P. fakaravensis , also separates the two species ( Fig. 15a, e ).

After examining P. corrugatus (von Martens, 1872) from the west and central Atlantic ( USNM 72340, 122786, 252325), it is clear that P. fakaravensis is morphologically close to the latter and may thus be considered a sibling species. It is surprising that neither Rathbun (1907) in her description of P. fakaravensis , nor Manning & Chace (1990) in recording and illustrating a male of P. corrugatus from Ascension I., mentioned this sharp similarity. Both species share a subrectangular carapace, with almost parallel lateral margins; coarse and hairy striae on the carapace; several longitudinal striae furnished with setae on the outer face of the chelae; abdominal tergites with short transverse striae; similarly shaped infraorbital margins, with a small protrusion distally followed by a deep indentation; and similar G1 ( Fig. 15a, f ). The two species can, however, easily separated using the relative striation of the abdominal tergites, which is more pronounced in P. fakaravensis than in P. corrugatus . This difference is especially obvious in males. Striae are also present on the thoracic sternites of P. fakaravensis but absent in P. corrugatus ( Fig. 3e , 1d ).

Davie (1998a) suggested that it was likely that P. fakaravensis had only recently become established or possibly introduced in the Hawaiian Is. because it was unusual that such a relatively large and distinctive intertidal crab, living in a major harbour on the island of Oahu, had not been previously noticed, especially given the large collections reported by Rathbun (1906) and the extensive collections made by Edmondson (1959).

Figures

FIGURE 1. —Pachygrapsus corrugatus (von Martens, 1872). a) dorsal view; b) front; c) left chela, outer face; d) male abdomen. a–c, ov. female 13.6 x 15.2 mm, Virgin Is. (USNM 72340); d) male 15.4 x 17.3 mm, Bahamas (USNM 122786).

FIGURE 3. —Pachygrapsus fakaravensis Rathbun (1907). a) dorsal view; b) front; c) left chela, outer face; d) right P5; e) male abdomen; f) female abdomen. a, b, d, f, ov. female 15.0 x 16.5 mm (MNHN B25782); c, e, holotype male 18.0 x 19.4 mm (USNM 32844).

FIGURE 14. —Infra–orbital margin: a) Pachygrapsus fakaravensis Rathbun (1907), ov. female 15.0 x 16.5 mm, Taiaro, French Polynesia (MNHN B25782); b) Pachygrapsus laevimanus Stimpson, 1858, neotype male 18.0 x 21.7 mm, Sydney, Australia (AM P7478); c) Pachygrapsus minutus A. Milne­Edwards, 1873, male 5.2 x 7.0 mm, Moruroa, French Polynesia (MNHN B29273); d) Pachygrapsus planifrons de Man, 1888, male 7.0 x 9.0 mm, Rangiroa, French Polynesia (UF 1490); e) Pachygrapsus plicatus (H. Milne Edwards, 1837), male 12.1 x 15.3 mm, Taiaro, French Polynesia (MNHN B29279); f) Pachygrapsus corrugatus (von Martens, 1872) ov. female 13.6 x 15.2 mm, Virgin Is. (USNM 72340); g) Pachygrapsus crassipes Randall, 1840, male 31.9 x 36.6 mm, Sagami Bay, Japan (NSMT Cr7516); h) Pachygrapsus gracilis (de Saussure, 1858), ov. female 8.5 x 11 mm, Angola (MNHN B12903); i) Pachygrapsus loveridgei Chace, 1966, male 8.1 x 10 mm, St. Helena I. (MNHN B17836); j) Pachygrapsus marmoratus (Fabricius, 1787), female 12.7 x 14.3 mm, Préfailles, France (MNHN B22654); k) Pachygrapsus maurus (Lucas, 1846), female 12.7 x 14.3 mm, Banyuls, France (MNHN B12933); l) Pachygrapsus transversus (Gibbes, 1850), male 17.0 x 22.5 mm, French Guiana (MNHN B16013). Scale bar 1 mm.

FIGURE 15. —Male gonopods: a) Pachygrapsus fakaravensis Rathbun (1907), holotype 18.0 x 19.4 mm, Fakarava, French Polynesia (USNM 32844), right G1, abdominal face (left) and detail of terminal portion, sternal face (right); b) Pachygrapsus laevimanus Stimpson, 1858, neotype 18.0 x 21.7 mm, Sydney, Australia (AM P7478), left G1, abdominal (left) and sternal face (right), setae omitted; c) Pachygrapsus minutus A. Milne­Edwards, 1873, cl 8.2 mm, Caroline Is., lateral (left) and abdominal face (right), setae omitted; d) Pachygrapsus planifrons de Man, 1888, 9.5 x 11.8 mm, Hawaiian Is. (USNM 29350), right G1, abdominal (left) and sternal face (right); e) Pachygrapsus plicatus (H. Milne Edwards, 1837), cl 11.7 mm, Hawaiian Is., lateral (left) and abdominal face (right); f) Pachygrapsus corrugatus (von Martens, 1872), cl 8.5 mm, Ascension I., left G1 abdominal face (left) and detail of terminal portion, setae omitted (right); g) Pachygrapsus crassipes Randall, 1840, cl 35.6 mm, California, lateral (left) and abdominal face (right) setae omitted; h) Pachygrapsus gracilis (de Saussure, 1858), cl 8.7 mm, Virgin Is., lateral (left) and abdominal face (right), setae omitted; i) Pachygrapsus loveridgei Chace, 1966, holotype 10.3 x 13.1 mm, St. Helena I. (USNM 112457), left G1, abdominal (left) and sternal face (right); j) Pachygrapsus marmoratus (Fabricius, 1787), cl 30.5 mm, Gibraltar, lateral (left) and abdominal face (right), setae omitted; k) Pachygrapsus maurus (Lucas, 1846), cl 8.5 mm, Canary Is., lateral (left) and abdominal face (right) setae omitted; l) Pachygrapsus transversus (Gibbes, 1850), cl 11.1 mm, Key West, Florida, lateral (left) and abdominal face (right), setae omitted. (c, e, g–l, from Chace, 1966, fig. 10–11; f, from Manning & Chace, 1990, fig. 43). Approximate magnification x 6 (x 12 for detail of terminal portion).