Syphopatella walshi (Reeve) is a commensal gastropod that is associated with gastropod shell occupied by a hermit crab, rather than directly attaching itself to the hermit crab’s body. Consequently, S. walshi might remain in gastropod shell at the time of shell exchange by hermit crabs. The present study aims at elucidating the host-finding behaviour of S. walshi, as it is not clear when and how S. walshi moves into a gastropod shell.

Specimens were collected from the stony shore of Magarisaki in Amakusa Shimoshima Island, south-western Japan. In order to observe their solitary behaviour, S. walshi was removed from gastropod shells and placed in a container with or without sea water to imitate low/high tide conditions. They were apparently more active when immersed in seawater, suggesting that S. walshi migrates when gastropod shells (or hermit crabs) remain underwater. Further, female individuals were observed to move despite a previous speculation to the contrary. These observations were considered in terms of life history and environmental adaptation.