EXCYSTATION OF APOSTOME CILIATES IN RELATION TO MOLTING OF THEIR CRUSTACEAN HOSTS

¹ Rockefeller Institute, New York, and the Marine Biological Laboratory, Woods Hole, Massachusetts

Observations and experiments have been made with the encysted phoronts of Gymnodinioides inkystans on the gills of the hermit crab (Pagurus longicarpus) and of Gymnodinioides sp. on the gills of the fiddler crab (Uca pugnax). The phoronts of both species would excyst in vitro, in a mixture of crab blood with sea water and antibiotics, and give rise to engorged trophonts, only if the cysts were taken from gills of a crab which was near molting. This excystation occurred somewhat more readily in the presence of blood from the same crab, near the molt, than in the presence of blood from a crab not close to molting. It is concluded that the encysted phoronts probably require a series of stimuli from the host in order to prepare them for the final stimulus which produces excystation just before the actual molt.