Anisocallisoma, Hendrycks & Conlan, 2003

Hendrycks, EA & Conlan, KE, 2003, New and unusual abyssal gammaridean Amphipoda from the north-east Pacific, Journal of Natural History 37, pp. 2303-2368 : 2313-2314

Anisocallisoma gen. nov.

Diagnosis

Head much deeper than long; lateral cephalic lobe small, rounded, situated near ventral margin of head; eye absent; antenna 1, peduncle 1 short and deep, accessory flagellum one-articulate, conical, lacking distal brush setae; mandibular molar, broadly triangular, non-triturative; maxilla 1, palp one-articulate, inner plate with one subapical seta; maxilla 2, plates subequal, ovate, inner plate with few medial setae; maxilliped, outer plate, medial margin crenate with four to six small spines; gnathopod 1, coxa small, tapering distally, basis swollen, propodus simple, dactylus minute; gnathopod 2, propodus palm weakly oblique; coxae 1–4 shallow, much less than corresponding peraeonite; coxa 4, ventral margin slightly tapering, rounded, posteroventral lobe weakly developed, posterior margin shallowly excavate; peraeopods 3–4, propodus slightly expanded, weakly prehensile; peraeopods 5–7, dissimilar, peraeopod 5 much shorter than peraeopods 6–7; urosomites 1 and 3 with a dorsal concavity; pleopods 1–3, anterior margin of inner ramus with fan-shaped clusters of setae on the distal segments; uropods 1–2, rami lacking spines; epimeron 2, ventral margin shallowly concave, with fringe of setae; telson broadest at mid-point, cleft 52%.

Type species Anisocallisoma armigera sp. nov. by monotypy.

Etymology

The genus name is a combination of the Greek anisos (unequal) referring to the difference in lengths between peraeopods 5 and 7 and callisoma, which refers to the close relationship to Eucallisoma .

Remarks

Anisocallisoma is distinguished from all other scopelocheirids by the extreme reduction in the number of setae of the maxilla 1 inner plate, having only one subapical seta, and in the palp of maxilla 1, which is one-articulate. The new genus appears closely related to Eucallisoma J. L. Barnard, 1961 with which it shares the expanded, glandular basis of gnathopod 1 and the peculiar, reduced dactylus. However, it can be differentiated easily from Eucallisoma by the shallow coxal plates, dissimilar peraeopods 5–7, maxilla 1 inner plate with only one subapical seta (vs>10+medial setae) and other characters in table 1.