It lives in the eastern Atlantic Ocean and Mediterranean Sea at depths between the intertidal zone and 60 m (200 ft).

Calliactis parasitica is up to 100 millimetres (3.9 in) tall, and 80 mm (3.1 in) wide,[2][3] with the base of the column being slightly wider.

[1] Above this lies the limbus (the junction between the basal disc and the column), and just above that are the relatively prominent cinclides (specialised pores), each on a small mound.

[2] Its Atlantic range extends from south-western Europe[2] as far north as the west coasts of Wales and Ireland,[3] and the English Channel.

[3] In the British Isles, the hermit crab is usually Pagurus bernhardus,[2] but other species may be associated with C. parasitica in other parts of its range.

[4] In aquarium settings, the mutualism between C. parasitica and the hermit crab Dardanus arrosor can break down; this breakdown is prevented or reversed when chemical signals from octopuses are present.