Observations on the theca of the motile phase of free-living and symbiotic isolates ofZooxanthella microadriatica(Freudenthal) comb.nov.

Abstract
A strain of Zooxanthella microadriatica (Freudenthal) comb.nov. has been isolated from decaying Chondrus crispus (L.) Stackh. The ultrastructure of this isolate has been compared to that of Z. microadriatica inhabiting Cassiopea Peron and Lesueur, 1809, sp. In an aqueous medium the cell cycle of both isolates consists of a coccoid non-motile phase alternating with a thecate motile phase.