actinie commensale

The cloak anemone (Adamsia palliata) is a sea anemone in the order Actiniaria found in shallow coastal waters of the northeastern Atlantic Ocean and Mediterranean Sea. Uniquely, this species forms an obligate mutualistic association with the hermit crab Pagurus prideaux, attaching itself to the shell occupied by the crab rather than anchoring to a hard substrate as most sea anemones do. The anemone wraps its basal disc around the shell opening, eventually growing a flexible extension called a carcinoecium that enlarges the effective volume of the shell as the crab grows, reducing the frequency with which the crab must find a new shell. In exchange, the crab carries the anemone to new food sources and the anemone's nematocyst-armed tentacles provide the crab with protection from predators. Adamsia palliata occurs from the intertidal zone to depths of around 200 meters, feeding on organic particles and small invertebrates captured by its tentacles. The mutualism between this anemone and its host crab represents one of the most specialized invertebrate symbioses in European coastal marine ecosystems.