Calcinus tubularis (Linnaeus, 1767)

Calcinus tubularis, the tube hermit crab, is a marine crustacean from the family Calcinidae. It can be found in the Mediterranean Sea and around several islands in the eastern Atlantic Ocean (Madeira, Canary Islands, ...).

Tube hermit crabs are small (up to 25 mm) and, like other hermit crabs, live in gastropod shells, which protects their soft rear body. Unique among hermit crabs, some members of Calcinus exhibit a sexual dimorphism regarding the choice of the shell in which they reside: male animals roam freely in shells of normal gastropods, whereas females inhabit the tubes of gastropods from the Vermetidae family, which are cemented to rocks. Therefore, female tube hermit crabs are rather sessile organisms.