Bivalve molluscs, Mytilus trossulus and Hiatella arctica, as facultative epibionts of the crab, Hemigrapsus sanguineus, infested by the rhizocephalan, Sacculina polygenea

At the period of sexual reproduction of the rhizocephalan parasite, Sacculina polygenea, the sacculinized crab, Hemigrapsus sanguineus, can serve as a temporary carrier for juvenile bivalve molluscs, Mytilus trossulus and Hiatella arctica as facultative epibionts. Such epizoans are never found on the crabs without the rhizocephalan externae or scars produced by the externae. The correlation between sacculinization and the bivalve epibionts is presumably due to maternal ‘brooding care’ with altering grooming behaviour of the crabs infested by S. polygenea.