Ethusa andamanica Alcock, 1894

Castro, Peter, 2005, Crabs of the subfamily Ethusinae Guinot, 1977 (Crustacea, Decapoda, Brachyura, Dorippidae) of the Indo-West Pacific region, Zoosystema 27 (3), pp. 499-600 : 513-515

Ethusa andamanica Alcock, 1894

( Fig. 4 )

Ethusa andamanica Alcock, 1894: 405 ; 1896: 284; 1899: 33. — Kemp & Newell 1912: 27. — Ihle 1916b: 153 (list), 155 (list).

Aethusa andamanica – Alcock & Anderson 1895: pl. 14, fig. 8.

? Ethusa andamanica – Doflein 1904: 27, 291 (list), pl. 13, figs 7, 8, 64. — Parisi 1914: 302, figs 3, 4.

TYPE MATERIAL. — Unknown (Zoological Survey of India, Calcutta?). The description was based on a male specimen ( Alcock 1894: 405), but Alcock (1899) refers to a female specimen. It is not clear if male specimens were not available or if the absence of a male alluded ( Alcock 1899: 34) was due to the absence of chelipeds and the second pair of pereopods in a male specimen and not to a male specimen. Kemp & Newell (1912: 29) refer to the “ types ” of the species. A juvenile female collected by the Investigator (stn 238, 13.IV.1898), originally at the Indian Museum but now deposited at BMNH (cl 6.8 mm, cw 7.1 mm; BMNH 1939.9.20.10) carries the label “ type ”. None of the two specimens measured by Alcock (1894, 1899), however, agree with the size of the BMNH specimen.

TYPE LOCALITY. — Andaman Sea, 362- 402 m.

MATERIAL EXAMINED. — Andaman Sea. Investigator , stn 238, 13°16’N, 93°8’E, 110-137 m, 13.IV.1898, “ type ”, Indian Museum, 1 juv. cl 6.8 mm, cw 7.1 mm ( BMNH 1939.9.20.10).

? Gulf of Aden. Meteor, cruise 5, stn 287 Ku, 12°16’N, 44°8.5’E, 472-479 m, 16.III.1987, 1 juv. ( SMF 29342).

DISTRIBUTION. — Off southwestern India ( Kemp & Newell 1912), Andaman Sea ( Alcock 1894), and Nicobar Is ( Doflein 1904); questionably from Japan ( Parisi 1914) and the Gulf of Aden. Depth: 110- 439 m (530 m in Doflein 1904) ( Fig. 34 ).

SIZE. — Maximum size: cl 10 mm (Kemp & Sewell 1912).

REMARKS

Alcock (1894) described the species from the Andaman Sea and placed it close to Ethusa orientalis Miers, 1886 , and, ultimately, as a “variety” of E. orientalis ( Alcock 1899: 34) . Unfortunately, the description ( Alcock 1894), later re-descriptions ( Alcock 1896, 1899; Kemp & Newell 1912), and the illustration of the species ( Alcock & Anderson 1895) were rather brief and there was no mention of the morphology of the anteri- or border of the endostome.

The similarities between the shape of the carapace of E. andamanica and E. orientalis ( Fig. 14A ) are indeed very close. Also similar are the relatively short and thick pereopods. The only differences given by Alcock (1894: 405) were the presence in A. andamanica of a smooth carapace, not well defined cervical and branchiocardiac grooves, and outer orbital teeth that were “not so prominent in relation to the front”. It is not known if the type material is extant but a juvenile female missing all pereopods (cl 6.8 mm, cw 7.1 mm; BMNH 1939.9.20.10) that was collected by the Investigator in the Andaman Sea off the Andaman Is and that carries the label “ type ” (see above) allowed the examination of the endostome. The extension of the anterior border of the endostome above the antennular fossae of the basal antennular articles, in contrast to a shorter endostome that just reaches to the basal antennular articles in E. orientalis ( Miers 1886: pl. 28, fig. 1a), plus the characters given by Alcock (1894), confirms the status of E. andamanica as a separate species.

Doflein (1904: 27) lists additional differences between the males of E. andamanica and E. orientalis , although the characters could not be confirmed due to the disappearance of Doflein’s male specimen from ZMB and the lack of an adult male specimen of E. andamanica . Furthermore, doubts about the identity of Doflein’s specimen as E. andamanica were raised by Kemp & Sewell (1912: 29), who had studied the type material of the species. Doflein’s specimen was collected from the Nicobar Is, near the type locality. Although the position of the anterior border of the endostome as shown in Doflein’s photographs ( Doflein 1904: pl. 13, figs 7, 8) agrees with the purported type at BMNH, the shape of the outer orbital teeth does not. They are slender, not triangular as in the BMNH specimen and Alcock’s figure ( Alcock & Anderson 1895: pl. 14, fig. 8).

Balss (1922: 120) considered E. andamanica a junior subjective synonym of Ethusa sexdentata ( Stimpson, 1858) , solely on the basis of its description and illustration ( Alcock & Anderson 1895: pl. 14, fig. 8) since there is no evidence that he examined the type material. Balss’ decision was seen by him as so obvious that “it did not need much explanation” (“bedarf keiner langen Beweisfürung”). The synonymy was followed by most authors ( Sakai 1937, 1976; Chen 1985, 1986, 1993, 1997), even if there were some reservations ( Nagai 1995: 59). The most obvious difference between the two species is the broadly triangular outer orbital teeth of E. sexdentata . Also diagnostic and clearly visible in the illustration of E. andamanica that Balss referred to ( Alcock & Anderson 1895: pl. 14, fig. 8) are the almost straight lateral borders that result from branchial regions that “do not bulge laterally”. In E. sexdentata the sides of the branchial regions are conspicuously inflated ( Sakai 1976: pl. 23, fig. 1; 1965: pl. 11, fig. 2; Miyake 1983: pl. 6, fig. 5; Chen 1985: fig. 5). Similar to E. sexdentata , however, are the long hairs along the margins of the frontal teeth.

There are strong similarities between E. andamanica and E. crassipodia n. sp. Both have relatively short and thick P2 and P3 but there are important differences (see description of E. crassipodia n. sp. below). The nearly parallel sides of the carapace and triangular outer orbital teeth of E. andamanica are similar to those of E. izuensis Sakai, 1937 , and E. zurstrasseni Doflein, 1904 . These two species can be differentiated from E. andamanica because the frontal teeth are narrower and the pereopods noticeably shorter and stouter in E. izuensis , while the carapace is more granular, the frontal teeth longer, and the outer orbital teeth narrower and pointed in E. zurstrasseni .

A specimen from Sagami Bay, Japan, that was identified as E. andamanica by Parisi (1914) could not be examined. It is most probably a misidentification since the species has never been recorded from Japan. A juvenile male from the Gulf of Aden (cl 5.7 mm, cw 5.4 mm; SMF 29342) was questionably assigned to E. andamanica . The outer orbital teeth were shorter than in the BMNH specimen and Alcock’s figure but their tips were much narrower as that shown in the left tooth of Alcock’s figure.

Figures

FIG. 4. — Ethusa andamanica Alcock, 1894, juv. “type” cl 6.8 mm, cw 7.1 mm, Andaman Sea off Andaman Islands, Investigator, stn 238, 110-137 m (BMNH 1939.9.20.10), dorsal surface of carapace. Scale bar: 5 mm.

FIG. 34. — Bathymetric distribution of Indo-West Pacific ethusine crabs.

FIG. 14. — Ethusa orientalis Miers, 1886, lectotype cl 15.7 mm, cw 15.1 mm, Fiji, E of Kadavu, Challenger, stn 173A, 567 m (BMNH 84-44); A, dorsal surface of carapace; B, left G1, ventral (left) and dorsal (right) views; C, right G2, dorsal view. Scale bars: A, 3 mm; B, C, 2 mm.