The sea anemone Calliactis tricolor and its association with the Hermit crab Dardanus venosus

The association of certain sea anemones and hermit crabs is established in different ways according to the species involved. The present study shows that the behaviour patterns of the two partners in associations between Calliactis tricolor (Lesueur) and Dardanus venosus (H. M. Edwards) in the Caribbean are similar to those seen in the Mediterranean C. parasitica and D. arrosor .
Although about half the crabs display an active behaviour pattern in laboratory trials, the anemone frequently settles on shells unaided and most C. tricolor respond to molluscan shells by clinging with their tentacles until the pedal disc can be attached. As a rule it is necessary for the anemone to relax and to cling to the shell if the crab is to be successful in transferring the anemone to its shell.
The behaviour patterns of D. venosus include a distinctive tapping of the edge of the base of C. tricolor after which the anemone is pulled or lifted off and transferred to the shell. An experimenter can also cause the anemone to relax and to detach itself by tapping the edge of the base with plastic rods after the manner of the crab.
The mechanisms by which the tentacles of Calliactis cling to, and by which the base settles upon, shells still remain to be elucidated. The participation of nematocysts in these processes could not be demonstrated in this study.
C. tricolor is found on some other pagurid and non-pagurid crabs in various localities. These associations need to be investigated fully in order that the behaviour patterns of C. tricolor may be correctly interpreted and compared with those of other species of Calliactis .