Abstract
Five specimens of Ostrea fluctigera Lamy, 1925 were collected from the Sagami Bay, adhering by their left valves to the lowest body whorl (near the aperture) of empty shells of several gastropod species, including those used by hermit crabs. In each case, the curved edge of the left valve precisely matched the curvature of the lowest body whorl of the snail shell, and both the left and right valves grew as an extension of the snail shell's aperture. The possibility of a mutualistic symbiosis between O. fluctigera and hermit crabs is discussed.
