Calcinus tubularis  Calcinus tubularis is a species of hermit crab. It is found in the Mediterranean Sea and around islands in the Atlantic Ocean, where it lives below the intertidal zone. Its carapace, eyestalks and claws are marked with numerous red spots. "C. tubularis" and its sister species, "C. verrilli", are the only hermit crabs known to show sexual dimorphism in shell choice, with males using normal marine gastropod shells, while females use shells of gastropods in the family Vermetidae, which are attached to rocks or other hard substrates. The genus "Calcinus" has its centre of diversity in the central Pacific Ocean, and only two species occur in the north-eastern Atlantic – "Calcinus paradoxus" and "Calcinus tubularis". "C. tubularis" is a chiefly Mediterranean species; its range extends from Madeira in the west to Lebanon in the east, with outlying records from Madeira, the Canary Islands, Cape Verde and Ascension Island. Although it is distinctively coloured, the sedentary behaviour of "C. tubularis" allows epibionts to colonise its shells, providing excellent camouflage, and it can easily go unnoticed; it was first reported on the coast of the Portuguese mainland in 2011, but is thought to have been living there for a long time. The carapace of "Calcinus tubularis" is bluish in colour, with many red spots, and extends forwards as a short, triangular rostrum. The eyestalks are white with similar red spotting, as is the last segment of each of the walking legs, and both the fixed and movable fingers of the claws. The colour scheme exists in a dark form and a light form, which appears to be linked to camouflage, particularly for females. "C. tubularis" is of "normal size" for a "Calcinus" species, frequently exceeding a carapace width of . "Calcinus tubularis" is a rare species, found below the intertidal zone. It is one of only two species of hermit crab (the other being the closely related "C. verrilli") in which sexual dimorphism in shell use has been observed. Males inhabit gastropod shells, chiefly those of "Pisania maculosa" or "Cerithium vulgatum", which they can move freely; females occupy the fixed tubes made by the vermetid snail "Lementina arenaria".