Ethusina Smith 1884

Ethusina Smith, 1884: 349. — A. Milne-Edwards & Bouvier 1902: 39. — Miers 1886: 331. — Ihle 1916b: 150 (in list). — Rathbun 1937: 77 (in key), 89. — Monod 1956: 84. — Balss 1957: 1610. — Guinot 1978: 249; 1979b: fig. 3. — Manning & Holthuis 1981: 42. — Hendrickx 1997: 73. — Chen & Sun 2002: 248. — Ng & Ho 2003: 71.

Ethusa – Alcock 1896: 281 (part). — Serène & Lohavanijaya 1973: 33 (part).

TYPE SPECIES. — Ethusina abyssicola Smith, 1884, by monotypy. Gender: feminine.

DIAGNOSIS. — Dorsal surface of carapace granular, with setae or short tomentum; some regions distinct, limited by grooves. Four frontal teeth. Basal antennular article very large, swollen, pushing antennae, eye peduncles, eyes laterally to near oblique position under orbits. Eye peduncles typically short or very short, often but not always immovable, on ventral surface of carapace, often not visible dorsally (rarely very long, enough to make eyes or considerable part of eye peduncles visible dorsally or, in males, beyond outer margins of the outer orbital teeth). Anterior border of endostome always well below posterior border of antennular fossae of basal antennular articles. P2, P3 relatively long (with long, slender meri), often reaching well over frontal teeth when folded.

REMARKS

The relative immobility of the eye peduncles in Ethusina in contrast to their mobility in Ethusa is a character difficult to assess and should not be used in their separation. The eye peduncles are certainly shorter in most species of Ethusina as a result of the expansion of the basal antennal article. The eye peduncles, however, do attain a considerable length in species like E. gracilipes (Miers, 1886) (Miers 1886: pl. 29, fig. 1, 1a) and E. exophthalma n. sp. (Fig. 21A, B), where the basal antennal article is greatly expanded as in other members of the genus. Obviously, the eyes in these species are “mobile” when pushed by the use of needles or forceps because of their length. The same can be said about other species where the eye peduncles are relatively long and in species where in the males the eyes protrude beyond the outer orbital teeth, as in the case of E. longipes Chen, 1987, E. paralongipes Chen, 1993, and E. robusta (Miers, 1886).

The presence in Ethusina desciscens (Alcock, 1896) of eye peduncles that are relatively mobile was considered by Alcock (1899: 35) as “the connecting-link between Ethusa and Ethusina ”. Such alleged mobility, however, was not noticed in any of the specimens of E. desciscens that were examined (see Remarks of E. desciscens below). Obviously, the apparent “mobility” of eye peduncles is also related to how long specimens have been fixed.

The allegedly ambiguous nature of Ethusa and Ethusina led Alcock (1896) and Serène & Lohavanijaya (1973) to consider Ethusina as a junior synonym of Ethusa. Serène & Lohavanijaya (1973) had a very limited amount of material at their disposal (only one specimen, which was misidentified) and they based their decision on the description and illustrations of the various species in the literature. The use of the relative mobility of the eyes as a character separating both genera also led Gore (1983: 211) to comment on the possible overlap between both genera.