Ethusina brevidentata Chen, 1993

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 : 549-552

Ethusina brevidentata Chen, 1993

Ethusina brevidentata Chen, 1993: 336 (key), 337, fig. 16. — Ng & Ho 2003: 72 (list).

Not Ethusina brevidentata – Chen 1997: 624 (= E. ocellata n. sp.).

TYPE MATERIAL. — Holotype: cl 8.5 mm, cw 8.0 mm, BIOGEOCAL, stn CP 283 ( MNHN-B 19099 ); paratypes: cl 10.0 mm, cw 10.0 mm, BIO- CAL, stn CP 72 ( MNHN-B 18401 );, same location ( IOAS); juv. cl 5.4 mm, cw 4.9 mm, BIOGEO- CAL, stn CP 272 ( MNHN-B 19096 ).

TYPE LOCALITY. — Loyalty Islands, 21°22.25’S, 166°31.07’E, 2370-2375 m.

MATERIAL EXAMINED. — New Caledonia. BIOCAL, stn CP 72, 22°10’S, 167°33’E, 2100 -2110 m, 4.IX.1985, 1 paratype ( MNHN-B 18401).

Loyalty Islands. BIOGEOCAL, stn CP 272, 21°00.04’S, 166°56.94’E, 1615-1710 m, 20.IV.1987, 1 juv. paratype ( MNHN-B 19096). — Stn CP 283, 21°22.25’S, 166°31.07’E, 2370-2375 m, 26.IV.1987, 1 holotype ( MNHN-B 19099).

DISTRIBUTION. — Known only from New Caledonia and the Loyalty Is ( Chen 1993). Depth: 1615-2375 m ( Fig. 34 ).

SIZE. — Maximum size: cl 9.1 mm, cw 9.0 mm ( Chen 1993), cl 10.0 mm, cw 10.0 mm (MNHN-B 18401).

REMARKS

Chen (1993: 337) distinguished her new species, Ethusina brevidentata , from E. dofleini Ihle, 1916 , by the presence of a conspicuously granular carapace and arched lateral borders, outer orbital teeth that are directed outwardly, broader than long telson, and meri of P2 and P3 that are “about 7 times” as long as high. There is no evidence, however, that she examined the type material of E. dofleini , and some of the E. brevidentata material she examined proved to belong to a new species, E. ocellata n. sp. The granular carapace of E. brevidentata is indeed a very diagnostic character that readily separates the two species. Differences with E. ocellata n. sp. are discussed in the description of the new species (see below).

Ethusina challengeri ( Miers, 1886) ( Figs 16 ; 17 ; 33D )

Ethusa (Ethusina) challengeri Miers, 1886 : xxxi, 331, pl. 28, fig. 2, 2a-c.

Ethusa (Ethusina) sinuatifrons – Miers 1886: 329, 332 (nomen nudum).

? Aethusina challengeri – Faxon 1895: 36 (= Ethusina faxoni Rathbun, 1933 ?).

Ethusina abyssicola challengeri – Ihle 1916a: 360; 1916b: 147, 153 (list), 156 (list). — Serène 1968: 40 (list). — Sakai 1937: 82, fig. 1f; 1956: 7 (list); 1976: 67, fig. 26f. — Miyake 1983: 199 (list) (not Ethusina abyssicola Smith, 1884 ).

Ethusina challengeri – Doflein 1904: 292 (list), fig. 65. — Chen 1993: 336 (key).

TYPE MATERIAL. — Holotype: cl 12. 9 mm, cw 12.9 mm, Challenger, stn 237 ( BMNH 84.44 ).

TYPE LOCALITY. — Pacific Ocean off Japan, 34°37’N, 140°32’E, 3429 m.

MATERIAL EXAMINED. — Indian Ocean. Mozambique Basin, SAFARI 1, stn 1, trawl CP 01, 29°52.6’S, 34°32.7’E- 29°52.3’S, 34°33.1’E, 2608 m, 20.VIII.1979, 1 ( MNHN-B 8775).

Mid-Indian Basin, SAFARI 2, stn 35, trawl CP 29, 12°56.8’S, 79°36.6’E- 12°55.0’S, 79°35.6’E, 4950- 4928 m, 20.VIII.1981, 1 ( MNHN-B 28697).

Japan. Challenger, stn 237, 34°37’N, 140°32’E, holotype ( BMNH 84.44).

Pacific Ocean. Shatskiy Rise, Hakuho-maru, cruise KH93-03, stn BT-3, 3274- 3287 m, 8.XI.1996, 1 ( CBM-ZC 6468).

Material of Ethusina abyssicola Smith, 1884 :

Atlantic Ocean. Off Massachusetts, Albatross, stn 2713, 38°20’N, 70°08.5’W, 3400 m, 17.IX.1886, 1, 1 ( MNHN-B 24048).

Off Azores, Talisman , stn 131, 38°38’N, 25°06’W, 2995 m, 22.VIII.1883, 3, 1 ( MNHN-B 24152). — Stn 133, 42°15’N, 21°17’W, 3975 m, 24.VIII.1883, 3, 1 ( MNHN-B 24149). — Stn 134, 42°19’N, 21°16’W, 4060 m, 24.VIII.1883, 4, 3 ( MNHN-B 24146), 1 ( MNHN-B 24151), 1 ( MNHN-B 24150).

DISTRIBUTION. — Japan and now from the Northwest Pacific Basin (Shatskiy Rise) and Indian Ocean ( Mozambique and Mid-Indian basins) ( Fig. 17 ). Depth: 2608 and 4928-4950 m ( Fig. 34 ).

SIZE. — Maximum size: cl 25.9 mm ( MNHN-B 28697), cl 12.6 mm, cw 12.1 mm ( MNHN-B 8775).

REMARKS

Miers referred to his new species by a second name, as “ Ethusa (Ethusina) sinuatifrons n. sp. ” in the list of the seven species of Ethusa known at that time ( Miers 1886: 329) and as “ Ethusa sinuatifrons ” in a comparison with another of his new species, Ethusina gracilipes ( Miers 1886: 332) . The name “ Ethusa (Ethusina) challengeri ”, however, was used first in the list of species collected in the Challenger stations ( Miers 1886: xxxi). This name was the one used in the formal description of the species and in the plate and legend that illustrated it ( Miers 1886: 331, pl. 28).

Ethusina challengeri can be distinguished from most other known Indo-West Pacific species of Ethusina by the shape of the frontal portion of its carapace: sinuous, concave median lobes without terminal teeth ( Fig. 16A ; Miers 1886: pl. 28, fig. 2, 2a; Sakai 1937: fig. 1f; 1976: fig. 26f), hence the alternate name used by Miers to name his species (see above). A sinuous front is also the case of E. dofleini Ihle, 1916 (see above) and in some specimens of E. dilobotus Chen, 1993 (see below). The eye peduncles are relatively large and oval, typically but not always tapering anteriorly toward the eye. They are clearly visible dorsally ( Fig. 16A ; Miers 1886: pl. 28, fig. 2). The retina, however, is much smaller than in other Indo- West Pacific species of Ethusina ( Fig. 16B ). The outer orbital teeth are tubercle-like, being short and obtuse. The G1 and G2 are illustrated here for the first time. The G1 are relatively short and stout, each with a band of many plumose setae near the tip ( Fig. 16C ).

Two specimens from the Indian Ocean, a large, fragmented female (cl 25.9 mm, MNHN-B 28697) and a male (cl 12.6 mm, cw 12.1 mm, MNHN-B 8775; Fig. 16 ), agree well with the female holotype ( BMNH 84.44) and a male from the northwestern Pacific Ocean (cl 13.0 mm, cw 12.3, CBM-ZC 6468). Although there are some differences (G1 of the Indian Ocean male each with a rounded tip and a slight reduction of the band of setae in contrast to slightly pointed tips, each with a band of setae that circles the distal end of the G 1 in the Pacific Ocean male; G2 of the Indian Ocean male each with an irregular tip [ Fig. 16D ] in contrast to a simple margin on the tip of the Pacific Ocean male; outer orbital teeth that are slightly larger in the Indian Ocean male than in the Pacific Ocean male), the differences are remarkably minor considering the widespread geographical distribution of the specimens.

Gore (1983: 211) commented on the apparent morphological overlap between E. challengeri and E. abyssicola Smith, 1884 , the type species of Ethusina . Ethusina abyssicola is restricted to very deep water in the tropical and temperate Atlantic Ocean, including the Caribbean Sea. Examination of a series of specimens of E. abyssicola from the Atlantic (material at MNHN originally identified by E.-L. Bouvier, A. Milne-Edwards, and M. Rathbun) has demonstrated that both species are clearly different from each other, however. The frontal teeth of E. abyssicola ( Smith 1884: pl. 2, fig. 1, 1a) are much more prominent and acute than in E. challengeri , where the medi- an lobes actually lack teeth ( Fig. 16A ). The P2 and P3 are thicker and shorter in E. abyssicola ( Smith 1884: pl. 2, fig. 1) than in E. challengeri ( Miers 1886: fig. 2), clearly extending well over the anterior border of the carapace in E. challengeri but only slightly over the anterior border in E. abyssicola . The G1 of E. abyssicola have a pointed tip and the setae at the base of the tips are long and plumose ( Gore 1983: fig. 3), whereas the tips are distinctively rounded and the setae at the base of the tips are short, thick, and arborescent in E. challengeri ( Fig. 16C ). The tip of the G1 of E. abyssicola illustrated by Manning & Holthuis (1981: fig. 9e) is more truncated than that of the specimens of the same species examined here but is nevertheless different from that of E. challengeri . The tips of the G2 are acute in E. abyssicola but wide and truncated in E. challengeri . Both species share a very small retina (see Doflein 1904: pl. 44, figs 1-3 for E. abyssicola ).

The identity of a female specimen collected from a depth of 4082 m in the Eastern Pacific and questionably referred to as E. challengeri by Faxon (1895) still remains uncertain since the specimen was not available for identification. Rathbun (1937: 93) questionably identified it as E. faxoni Rathbun 1933 , an Eastern Pacific species. The wide geographical distribution of E. challengeri ( Fig. 17 ) and the great depths it inhabits, however, do not preclude its restriction to the Indo-West Pacific region.

Figures

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

FIG. 16. — Ethusina challengeri (Miers, 1886), cl 12.6 mm, cw 12.1 mm, Mozambique Basin, SAFARI 1, stn 1, trawl CP 01, 2608 m (MNHN-B 8775); A, dorsal surface of carapace; B, ventral view of anterior portion of body; C, right G1, ventral (left) and dorsal (right) views; D, left G2, dorsal view. Scale bars: A, 5 mm; B, D, 2 mm; C, 1 mm.

FIG. 17. — Geographical distribution of Ethusina challengeri (Miers, 1886).

FIG. 33. — A, Ethusa granulosa Ihle, 1916, cl 14.7 mm, cw 14.6 mm, Vanuatu, west coast of Malekula, MUSORSTOM 8, stn DW 1061, 458-512 m (MNHN-B 28698) (photograph by J.-L. Menou, IRD, Nouméa); B, Ethusa hawaiiensis Rathbun, 1906, cl 6.7 mm, cw 6.2 mm, Vanuatu, S of Anatom, MUSORSTOM 8, stn CP 963, 400-440 m (MNHN-B 28538) (photograph by J.-L. Menou, IRD, Nouméa); C, Ethusa indica Alcock, 1894, cl 7.8 mm, cw 7.8 mm, Vanuatu, SE of Éfaté, MUSORSTOM 8, stn CP 1036, 920-950 m (MNHN-B 28560) (photograph by J.-L. Menou, IRD, Nouméa); D, Ethusina challengeri (Miers, 1886), cl 25.9 mm, Mid-Indian Basin, SAFARI 2, stn 35, trawl CP 29, 4950-4928 m (MNHN-B 28697) (photograph by P. Briand, IFREMER); E, Ethusina macrospina Ng & Ho, 2003, cl 10.4 mm, cw 11.0 mm, Taiwan, off southwest coast, TAIWAN 2003, stn CD 203, 635-868 m (NTOU) (photograph by T.-Y. Chan, NTOU).