Ethusina exophthalma, 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 : 560-562

Ethusina exophthalma n. sp.

( Fig. 21 )

TYPE MATERIAL. — Holotype: cl 7. 1 mm, cw 6.9 mm, MUSORSTOM 10, stn CP 1331 ( MNHN-B 28710 ); paratypes: cl 7. 6 mm,

damaged; cl 8.2 mm, cw 8.6 mm, same station ( MNHN-B 28711).

TYPE LOCALITY. — Fiji, Bligh Water between Viti Levu and Vanua Levu islands, 17°02.4’S, 178°01.8’E, 694- 703 m.

MATERIAL EXAMINED. — Fiji. MUSORSTOM 10, stn CP 1331, 17 °02. 4’S, 178°01.8’E, 694-703 m, 8.VIII.1998, 1 holotype ( MNHN-B 28710), 1 paratype, 1 ovig. paratype ( MNHN-B 28711).

ETYMOLOGY. — From exo and ophthalmos (Greek for out and eye, respectively) in reference to the protruding eyes that extend well outside the lower margins of the orbits and can be clearly seen dorsally, a unique character among the species of Ethusina .

DISTRIBUTION. — Known only from Fiji. Depth: 694- 703 m ( Fig. 34 ).

SIZE. — Maximum size: cl 7.6 mm (MNHN-B 28710), cl 8.2 mm, cw 8.6 mm (MNHN-B 28711).

DESCRIPTION

Carapace ( Fig. 21A ) almost as broad as long in males, slightly broader than long in paratype female; dorsal surface with conspicuous, small granules. Urogastric, cardiac regions slightly elevated, bordered by conspicuous grooves; cervical, branchial grooves shallow. Branchial regions inflated along sides.

Anterior border of carapace ( Fig. 21A ) with acute, straight outer orbital teeth, longer than but not reaching frontal teeth. Frontal teeth nearly triangular, acute to obtuse tips, lateral frontal teeth nearly equal or slightly shorter than median frontal teeth. Orbital sinuses very broad, U-shaped, nearly symmetrical, inner margins almost straight, outer J-shaped; lateral frontal sinuses U-shaped; median frontal sinus V-shaped, wider than lateral frontal sinuses (nearly equal in paratype female) but much narrower than orbital sinuses.

Eye peduncles ( Fig. 21B ) much longer than cornea, 1.3-1.6 times eye diameter; very mobile. Eyes and most of eye peduncles visible dorsally across orbits.

Anterior border of endostome ( Fig. 21B ) lies well below posterior border of antennular fossae of basal antennular articles.

Male chelipeds (P1) smooth, equal; propodi slen- der, 0.7 as long as fingers; fingers slender, with broad cutting edges. Chelipeds of female paratype similar to male chelipeds except few broad, round teeth.

P2, P3 relatively long; length of P2 meri 1.0- 1.4 times cl, P2 meri 6.1-7.6 times longer than broad. P4, P5 with few short hairs, more conspicuous in female paratype; P5 dactyli thick, curved.

Male abdomen with four somites (3-5 fused, basal half swollen), rounded telson. Somite 1 length 3.6 times as broad, somite 6 slightly trapezoidal. Female abdomen with six somites, broad, rounded telson; somite 3 broadest, somite 6 longest.

G1 ( Fig. 21C ) slender; each distal end rounded, symmetrical, laterally expanded on each inner margin, fringes of spines; G2 ( Fig. 21D ) relatively long, each distal part narrower; curved distal end, pointed tip.

REMARKS

Together with Ethusina gracilipes ( Miers, 1886) , E. exophthalma n. sp. is unique among the known species of Ethusina by having greatly elongated eye peduncles, which allow the eyes to project well outside the lower margin of the orbital sinuses and are therefore not concealed or mostly concealed by the carapace as in most species of Ethusina .

The eye peduncles are also long in E. gracilipes ( Miers 1886: pl. 29, fig. 1, 1a) but not nearly as long as in E. exophthalma n. sp. Also in contrast to E. gracilipes , the orbital sinuses are very broad and U-shaped (wider than in E. gracilipes ) and the dorsal surface of the carapace conspicuously more granular. The P2 and P3 are much more slender in E. gracilipes (P2 meri 10 times longer than broad) than in E. exophthalma n. sp. (P2 meri 6.1-7.6 times longer than broad). There are also differences in the G1, which are asymmetrical and spade-like, being broadened along the inner margins and having pointed tips in E. gracilipes , in contrast to nearly symmetrical and round-tipped in E. exophthalma n. sp. ( Fig. 21C ).

Figures

FIG. 21. — Ethusina exophthalma n. sp., holotype cl 7.1 mm, cw 6.9 mm, Fiji, Bligh Water between Viti Levu and Vanua Levu islands, MUSORSTOM 10, stn CP 1331, 694-703 m (MNHN-B 28710); A, dorsal surface of carapace; B, ventral view of anterior portion of body; C, left G1, ventral view; D, left G2, ventral view. Scale bars: A, 5 mm; B, 2 mm; C, D, 1 mm.

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