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Biology/Natural History: This species is said to generally live symbiotically with the sponge Suberites latus or Suberites ficus, which dissolves and overgrows its shell. This specimen was in a "house" made largely or entirely of the hydroid Hydractinia milleri. This hydroid is said to encrust shells which have hermit crabs living in them, and eventually to overgrow the shell as the crab grows. The hermit crab frequently rubs the flagellae of its second antennae over the hydroid colony. In another Hydractinia-hermit crab symbiosis this behavior was found to result in the hermit crab gathering and eating some of the plankton the Hydractinia had captured.
The presence of Hydractinia on a hermit crab seems to at least partially deter predation by octopus. Octopus usually readily capture hermit crabs and other crustaceans. However, an octopus clearly thinks twice about attacking a hermit crab with Hydractinia on its shell. Click here for a movie showing how octopus deal with Hydractinia-covered hermit crabs.