For the first time carnivorous bivalve mollusc Cuspidaria trosaetes Dall, 1925 was recorded in the north-western Sea of Japan. There was only one species of Cuspidaria, C. ascoldica, previously known in this region. Alive specimens of C. trosaetes were collected in the Tatarsky Strait on the continental slope on muddy sediment at the depths of 531–589 m. Stomach contents of C. trosaetes consist of foraminifers, copepods and rissoid gastropods. Cuspidaria trosaetes was selected as a type species of a monotypic subgenus C. (Nordoneaera) Okutani, 1985, which is now considered a separate genus, based on the presence of a thick shell without sculpture and with thick periostracum, as well as a short rostrum. The first obtained data on anatomy of C. trosaetes suggest its close affinity with the type species of the genus Cuspidaria, C. cuspidata. Cuspidaria trosaetes and C. cuspidata share such features as the presence of 5 pairs of septal pores, thin elongated posterior labial palps and the presence of two rows of papillae on the rim of the common siphonal sheath. Taking into account new data we propose to synonymize the monotypic genus Nordoneaera with the genus Cuspidaria.