Ethusina gracilipes ( Miers, 1886 )

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 : 563-564

Ethusina gracilipes ( Miers, 1886)

( Fig. 22 )

Ethusa (Ethusina) gracilipes Miers, 1886 : xxviii, 332, pl. 29, fig. 2, 2a-c. — Alcock 1899: 34.

Not Aethusina gracilipes – Faxon 1895: 36.

Ethusina gracilipes – Doflein 1904: 292 (list), fig. 65 (part). — Serène 1968: 40 (list). — Chen 1993: 336 (key). — Ng & Ho 2003: 72 (list).

Not Ethusina gracilipes – Rathbun 1906: 891 (= E. isolata n. sp.).

Not Ethusina gracilipes – Rathbun 1937: 94, pl. 30, fig. 4, pl. 31, fig. 4 (= E. isolata n. sp. [part]).

Not Ethusina gracilipes – Ihle 1916b: 146, 151 (list), 152 (list), 153 (list) (part), 156 (list) (part) (= E. robusta ( Miers, 1886)) .

Not Ethusa gracilipes – Serène & Lohavanijaya 1973: 35 (key), 35, figs 56-59, pl. 4, figs C, D. — Serène & Vadon 1981: 119, 121 (= E. indica Alcock, 1894 ).

Not Ethusina gracilipes – Luke 1977: 33. — Lemaitre & Álvarez-León 1992: 50. — Hendrickx 1995: 128; 1997: 166. (= Ethusina sp. )

? Ethusina gracilipes – Marumura & Kosaka 2003: 23.

TYPE MATERIAL. — Lectotype: cl 8.2 mm, cw 8.3 mm; paralectotypes: cl 8.2 mm, cw 8.5 mm, ovig. cl 8.1 mm, cw 8.6 mm, Challenger, stn 207, 1280 m ( BMNH 84.44 ).

Miers (1886) based his description on four specimens without selecting a holotype. One of the extant three syntypes, the only male (a second male mentioned by Miers is missing), is hereby designated the lectotype and the remaining two specimens, both females, are the paralectotypes.

TYPE LOCALITY. — Philippine Islands, Sibuyan Sea, 12°21’S, 122°15’E, 1280 m.

MATERIAL EXAMINED. — Philippine Islands. Sibuyan Sea, Challenger, stn 207, 12°21’S, 122°15’E, 1280 m, 1 lectotype, 1 paralectotype, 1 ovig. lectotype ( BMNH 84.44).

DISTRIBUTION. — Western India ( Alcock 1899) and Philippine Is ( Miers 1886) ( Fig. 22 ). Depth: 1280 m ( Miers 1886), 1520 m ( Alcock 1899) ( Fig. 34 ).

SIZE. — Maximum size: cl 8.2 mm, cw 8.3 mm (BMNH 84.44), cl 8.2 mm, cw 8.5 mm (BMNH 84.44).

REMARKS

Very characteristic of Ethusina gracilipes is the elongated, highly mobile eye peduncles, 1.1 times the eye diameter. The eye peduncles allow the eyes to project well outside the edge of the orbit ( Miers 1886: pl. 29, fig. 1, 1a) and are therefore not concealed or mostly concealed by the carapace as in most species of Ethusina . Nevertheless, the eyes were described as “small” and tapering “very slightly, if at all” ( Miers 1886: 332). Also diagnostic are the very slender chelipeds, P2, and P3, conspicuously swollen branchial and pterygostomial regions, and a conspicuously demarcat- ed and depressed gastric region, all of which are visible in Miers’ figures ( Miers 1886: pl. 29, fig. 1, 1a).

The G1 of the lectotype (cl 8.2 mm, cw 8.3 mm, BMNH 84.44) are slender, each with a pointed distal end, laterally expanded on the inner margins, and fringes of relatively thick spines along both edges of the distal ends.

One of the differences Miers used to distinguish between E. gracilipes and E. robusta ( Miers, 1886) was the relative length and width of the pereopods. Indeed, the pereopods of the specimens illustrated by Miers (1886: pl. 29, fig. 1, 2) are visibly much longer and more slender in E. gracilipes than in E. robusta . The folded P2 and P3 clearly extended well over the anterior border of the carapace in the type material of E. gracilipes but only slightly over the anterior border in the type material of E. robusta . The length of P2 meri was 1.2 times cl in the type material (N = 2) of E. gracilipes , 0.9-1.0 (mean of 1.0) times cl in the type material (N = 4) of E. robusta ; P2 meri 10 times longer than broad in E. gracilipes in contrast to 8.4 to 10.2 (mean of 9.1) in E. robusta . The differences between the eye peduncles and eyes of E. gracilipes and E. robusta can be clearly observed in Miers’ figures and were confirmed in the type material. The wide, short, rounded eye peduncles of the type material of E. robusta were 2.7 times the eye diameter in contrast to 1.1 times the eye diameter in E. gracilipes . The frontal teeth, which are of similar size in both species, are shown to be much longer in E. gracilipes than in E. robusta in Miers’ figures ( Miers 1886: pl. 29, figs 1, 2) but only because the teeth had been severed in the large female of E. robusta that was illustrated (cl 15.2 mm, cw 15.6 mm, BMNH 84.44; see Remarks of E. robusta below). Rathbun (1906, 1937) synonymized E. gracilipes with E. robusta and used the name E. gracilipes to refer to species from the Americas (following Faxon 1895) and the Hawaiian Is that belong to other species. The Hawaiian Is specimens are being described as a new species, E. isolata n. sp. (see below). Material from the Eastern Pacific region (Lemaitre & Álvarez-León 1992; Hendrickx 1997) probably belongs to an Eastern Pacific endemic species absent in the Indo-West Pacific. The two specimens from the Galápagos Is shown in a photograph by Rathbun (1937: pl. 30, fig. 4, pl. 31, fig. 4) are definitely not E. gracilipes . In these specimens the eyes are not visible dorsally and the teeth along the anterior border of the carapace are much shorter than in Miers’ species.

Two of the four extant Siboga specimens from Indonesia identified by Ihle (1916b) as E. gracilipes proved to be E. robusta (see Remarks of E. robusta below). Specimens from the South China Sea identified as E. gracilipes by Serène & L o h a v a n i j a y a (1 9 7 3) a n d S e r è n e & V a d o n (1981) appear to be identical to E. indica Alcock, 1894 , as previously mentioned by Chen (1985: 189, 191). The identity of a specimen of E. gracilipes from Japan ( Marumura & Kosaka 2003) needs to be verified.

Figures

FIG. 22. — Geographical distribution of Ethusina gracilipes (Miers, 1886) (G) and Ethusina robusta (Miers, 1886) (●).

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