Ethusina isolata, Castro, 2005

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 : 583-586

Ethusina isolata n. sp.

( Fig. 31 )

Ethusina gracilipes – Rathbun 1906: 891; 1937: 94 (part) (not E. gracilipes ( Miers, 1886)) .

TYPE MATERIAL. — Holotype: cl 9.2 mm, cw 9.2 mm, Albatross, stn 4028 ( USNM 29933 ); paratypes: cl 6.3 mm, cw 5.9 mm, Albatross, stn 4132 ( USNM 29934 ); cl 6.4 mm, cw 6.1 mm, Albatross, stn 3909 ( USNM 29932 ).

The female specimen was selected as the holotype because it is the only specimen with all pereopods attached.

TYPE LOCALITY. — Hawaiian Is, Kauai, off Kokole Pt, 21°54.58’N, 159°49.58’W, 470- 573 m.

ETYMOLOGY. — From isolatus (Latin for isolated) in reference to the isolated geographical location of the species, so far known only from the Hawaiian Is.

MATERIAL EXAMINED. — Hawaiian Islands. Albatross, stn 3909, Oahu, off Diamond Head, 564-589 m, 5.V.1902, 1 paratype ( USNM 29932). — Stn 4028, Kauai, off Kokole Pt, 21°54.58’N, 159°49.58’W, 812-873 m, 24.VI.1902, 1 holotype ( USNM 29933). — Stn 4132, Kauai, off Hanamaulu, 22°01.5’N, 159°21.16’W, 470-573 m, 1.VII.1902, 1 paratype ( USNM 29934).

DISTRIBUTION. — Known only from the Hawaiian Is. Depth: 416-1100 m ( Fig. 34 ).

SIZE. — Maximum size: cl 6.4 mm, cw 6.1 mm (USNM 29932), cl 9.2 mm, cw 9.2 mm (USNM 29933).

DESCRIPTION

Carapace ( Fig. 31A ) as long as broad in female holotype, slightly longer than broad in males; dorsal surface with few short, sparse setae, conspicuous small granules. Urogastric, cardiac regions elevated, urogastric region bordered by conspicuous lateral grooves; branchial grooves very shallow. Branchial regions slightly inflated along sides. Anterior border of carapace ( Fig. 31A ) with triangular, acutely tipped outer orbital teeth, straight in female holotype, directed outwardly in males, longer than but not reaching as high as frontal teeth. Frontal teeth longer and more conspicuous in males; lateral frontal teeth slender, slightly shorter than triangular median frontal teeth in female holotype, shorter than acute median frontal teeth. Orbital sinuses broad, U-shaped in female holotype, V-shaped in males; small, short vertical fissure at dorsal lower margin of each sinus; inner margins J-shaped, outer oblique; lateral frontal sinuses asymmetrical, obliquely U-shaped; median frontal sinus U-shaped in female holotype, V-shaped in males, wider than lateral frontal sinuses but narrower than orbital sinuses.

Eye peduncles wide, slightly longer than or as long as cornea, immobile. Most of eyes visible dorsally. Anterior border of endostome lies well below posterior border of antennular fossae of basal antennular articles.

Chelipeds (P1) smooth, equal or nearly equal; propodi slender, almost as long as fingers; fingers very slender, margin nearly smooth in female paratype, broad cutting edges in males.

P2, P3 ( Fig. 31A ) relatively short, granular articles except dactyli; length of P2 meri 0.8 times cl in female holotype, 1.1 in males, P2 meri 8.3-8.9 times longer than broad. P4, P5 with very sparse, short hairs; P5 dactyli relatively slender, curved.

Male abdomen with four somites (3-5 fused, basal half swollen), triangular telson. Somite 1 length 2.3 times as broad, somite 6 rectangular. Female abdomen with six somites, broad, triangular telson; somite 3 broadest, somite 6 longest. G1 ( Fig. 31B ) very slender; distal third narrow, each tip straight, slightly rounded, short spines along tip, inner margins; G2 relatively short, each distal part broad; straight distal end, blunt tip.

REMARKS

Ethusina isolata n. sp. is known from only three specimens collected from the Hawaiian Is by the Albatross and identified by Rathbun (1906: 891) as E. gracilipes ( Miers, 1886) . The Hawaiian specimens are not conspecific with Miers’ species, which is characterized by elongated, highly mobile eye peduncles that project the eyes well outside the orbits and the presence of conspicuously inflated branchial and pterygostomial regions ( Miers 1886: pl. 29, fig. 1, 1a). The specimens do not agree with any of the described species of Ethusina and are therefore regarded as undescribed.

Ethusina isolata n. sp. shares several characters with the two other species of Ethusina that are found only along the eastern limits of the Indo- West Pacific region, E. crenulata n. sp. and E. huilianae n. sp. They all share a similar shape of carapace, P2 and P3, and very slender G1. Differences among the three species are summarized in Table 1.

Figures

FIG. 31. — Ethusina isolata n. sp.; A, holotype cl 9.2 mm, cw 9.2 mm, Hawaiian Islands, Kauai, Albatross, stn 4028, 812-873 m (USNM 29933), dorsal surface of carapace and P2; B, paratype, 6.3 mm, cw 5.9 mm, Hawaiian Islands, Kauai, Albatross, stn 4132, 470-573 m (USNM 29934), left G1 ventral view with G2 in situ (left), dorsal view (right). Scale bars: A, 5 mm; B, 1 mm.

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