Differences in the spatial distribution and shell morphology of Thylacodes adamsii (Gastropoda: Vermetidae) distributed in the Pacific and the Sea of Japan coastal areas of Japan

Abstract

Thylacodes adamsii is a sessile gastropod and common inhabitant of rocky shores along the warm temperate coastal regions of Japan. We investigated the spatial distribution of this species in Shirahama facing to the Pacific Ocean, and in Maizuru facing to the Sea of Japan. Results showed that this species inhabits the middle intertidal zone in low densities in Shirahama, whereas it lives in high densities on oyster shells in the subtidal zone in Maizuru. Additionally, distinct shell morphology was found in the populations between the two localities. Observations of radular morphology suggest that they are most probably conspecific. Distinct shell morphology may be a result of adaptation to the different habitats.