On some species of the genera Campylaspenis and Campylaspis (Crustacea, Cumacea, Nannastacidae) from the Sea of Japan (Northwest Pacific), with description of a new species of Campylaspenis.

The cumacean genus Campylaspenis (Cumacea: Nannastacidae) currently consists of two species, characterized by an unusual character, the presence of a pair of large penial lobes in adult males, the only character which distinguishes the genus from the genus Campylaspis. This study, based on specimens from the Sea of Japan, describes a new species, C. sigeogamoi sp. nov, and Campylaspis pisum Vassilenko & Tzareva, 2004 is re-described and transferred to the genus Campylaspenis. Additionally, two species of Campylaspis, C. crispa (re-described) and C. brevirostris (briefly re-described) are reported. These four species with a carapace with three oblique ridges closely resemble each other except that the two Campylaspenis males have a pair of large penial lobes, suggesting that these four species may share a common ancestor. Among them, Campylaspenis sigeogamoi and Campylaspis crispa are similar to each other in the normal pseudorostrum and no distinct transverse ridge on the frontal lobe of the carapace, and Campylaspenis pisum is similar to Campylaspis brevirostris including the short, upturned pseudorostrum and transverse ridge on the frontal lobe. The similarity of the two pairs of species suggests that presence of penial lobes may not be a generic level character in this group.