Reversible metamorphosis in coral planula larvae

When planktonic planula larvae of the scleractinian coral Pocillopora damicornis settle, they secrete a calcareous exoskeleton for substrate attachment and metamorphose into a benthic polyp complete with mouth, tentacles, and mesenteries. If, however, these polyps are stressed within 3 d of settlement, they can retract all tissue from the skeleton and revert to a motile planktonic form resembling the initial larval stage. These 'secondary larvae' are capable of resettling and once again metamorphosing into a benthic polyp. Also, planulae may undergo a pelagic metamorphosis to a planktonic polyp with mouth and tentacles. This developmental plasticity permits an enhanced microhabitat selection ability, and has likely contributed to the broad dispersal of this pan-Pacific species.