The behaviour of algal cells towards egg capsules ofConvoluta roscoffensisand its role in the persistence of theConvoluta-alga symbiosis

Egg capsules collected from wild colonies and laboratory cultures of Convoluta roscoffensis carried a variety of organisms. However, algae were not found on capsules laid by animals that had previously been washed free of exogenous algae. It is concluded that symbiotic algae are not transmitted during reproduction of laboratory-maintained C. roscoffensis and that all the algae associated with the capsules are free-living. Cells of all Platymonas and Tetraselmis species tested aggregated around and adhered to the capsules of C. roscoffensis. No evidence for chemotaxis of P. convolutae and T. tetrathele towards the capsules was found.