The occurrence of a new species of Isocyamus (Crustacea,Amphipoda) from Australian and Japanese Pilot Whales,with a key to species of Isocyamus

Isocyamus deltobranchium n. sp. is described from the short-finned pilot whale, Globicephala macrorhynchus Gray 1946 in Japanese waters, and the long-finned pilot whale, Globicephala melaena (Traill 1809) from Tasmania, Australia. To date only two species of Isocyamus have been described: I. delphini (Geurin-Meneville 1836) Gervais and Beneden, 1859 and I. kogiae Sedlak-Weinstein 1991. The present species differs from I. delphini and I. kogiae in having large triangular accessory gills in the males, and a bilobed maxilla 2. It is similar to I. delphini in ventral spination, and single serrated comb on dactylus of gnathopod 1. Isocyamus deltobranchium n. sp. is the second species of cyamid reported from the long-finned pilot whale and the first from the short-finned pilot whale. The occurrence of I. deltobranchium in the northern and southern hemispheres, and in two different host species, suggests that the ranges of the host species overlap.