Five new species of the tribe Ischyrocerini Stebbing, 1899 from Japan (Crustacea: Amphipoda: Ischyroceridae)

Five new species of the ischirocerid amphipods, two species of Microjassa Stebbing, 1899 and three species of Neoischyrocerus Conlan, 1995, are described from Japanese waters between 0–40 m depth. Microjassa excavata sp. nov. is characterized by the strongly excavated posteroventral margin of the male coxa 2, and M. vestigialis sp. nov. by the vestigial accessory flagellum of antenna 1. Neoischyrocerus furcatus sp. nov. and N. praecox sp. nov. share the low ridges on the lateral and medial surfaces of dactyli of the gnathopods and pereopods 5–7, but N. praecox is different from N. furcatus in the small size and the early maturation. Moreover, Neoischyrocerus longipes sp. nov. has the remarkably long pereopod 5 in both sexes. Diagnoses of the both genera are emended and a key to the species of the tribe Ischyrocerini Stebbing, 1899 in Japan is provided.