On the antarcturid genus Fissarcturus (Isopoda: Valvifera): description of F. argentinensis n. sp., first description of the male of F. patagonicus (Ohlin, 1901), and biogeographic remarks on the genus

Abstract Fissarcturus argentinensis n. sp. (Valvifera, Isopoda) is described from the Mar del Plata submarine canyon. This species can be separated from other species of the genus by: (1) its medium-sized eyes, (2) the number and arrangement of spines on the body surface, and (3) the pleopod I with the endopod smaller than the exopod and lacking plumose setae on both rami. The distribution of F. patagonicus ( Ohlin, 1901 ) is extended, and the male is described and illustrated for the first time. Remarks on the penial plate, a character that has received little attention in the taxonomy of the genus, are provided. The distribution data of the species currently assigned to Fissarcturus are compiled and updated. A general trend of eye size reduction with depth is suggested for the members of this genus.