New and little-known shell-bearing heterobranch mollusks (Heterobranchia: Aplustridae and Cephalaspidea) from the bathyal zone of the northwestern part of the Sea of Japan

Seven species of the shell-bearing heterobranch gastropods collected during Cruise 51 of R/V Akademik M.A. Lavrentyev in the northern part of the Sea of Japan represent the new data on the fauna of Heterobranchia in the bathyal zone from this area. Taxonomic descriptions of two new species, Parvaplustrum japonicum sp. nov., and Retusa lata sp. nov., are presented herein with remarks on morphology and distribution. The finding of Toledonia cf. limnaeoides (Odhner, 1913) is the first record of the genus Toledonia for the northern Pacific. The present records for Diaphana hiemalis (2693-2725 m) and Cylichna toyamaensis (1001-2555 m) are the deepest.