Symbiodinium gen. nov. and Symbiodinium microadriaticum sp. nov., a Zooxanthella: Taxonomy, Life Cycle, and Morphology.*

SYNOPSIS. The life cycle of the zooxanthella of Cassiopeia sp., as determined by in vitro studies, includes a dominant vegetative autotrophic stage, a reproductive cyst producing autospores, aplanospores, or motile gymnodinioid zoospores, or possible gametes. The predominance of these stages is partially determined by environmental factors, e.g., photoperiodicity. As none of the existing genera of free‐living or parasitic algae are wholly applicable to this organism, a new genus, Symbiodinium , is proposed. The type species, S. microadriaticum , is described.