Division Synchrony in Primary Cultures of an Endozoic Dinoflagellate1

SUMMARY Division cysts of zooxanthellae harbored by Anthopleura elegantissima were isolated from random host‐associated populations by their preferential attachment to plastic surfaces. By selecting cysts at similar stages in the cell cycle, synchronous division, excystation, and daughter cell reencystment were obtained in a medium enriched with amino acids. The interval of DNA synthesis in a single growth cycle was determined by pulse‐labeling with radioactive thymidine. Analysis of the sequence of morphologic changes within such cycles suggested that the initial selection procedure isolates G2 cells. The transit time from first generation G2 division cysts to subsequent reentry into G2 was about 70 hr.