COMPARATIVE ULTRASTRUCTURE OF THE ZOOSPORES OF 8 SPECIES OF CHARACIUM (CHLOROPHYTA)

Eight species of Characium can be separated into three groups on the basis of zoospore basal body orientation. In group I species, C. starrii, C. fusiforme and C. vacuolatum, the basal bodies are in the clockwise absolute orientation, mature vegetative cells are uninucleate, the pyrenoid is penetrated by thylakoids and the zoospores are covered by a thin cell wall. In group II, C. pseudopolymorphum, C. hindakii, C. californicum and C. typicum, the basal bodies are directly opposed, mature cells are multinucleate, the pyrenoid is not penetrated by thylakoids and the zoospores are naked or covered by a thin, fuzzy coating. In group III C. perforatum, the basal bodies are counterclockwise, mature cells are uninucleate, the pyrenoid is penetrated by thylakoids and the zoospores are naked. The following taxonomic treatment is proposed: Group I should be included in the genus Chlamydopodium; Characiopodium gen. nov. is erected for the species of Group II; and Fusochloris gen. nov. is erected for Characium perforatum of Group III. It appears that convergence of similar vegetative cell morphology has occurred multiple times among the chlorococcalean algae including a similar combination of features also observed in three groups within the genus ''Neochloris'' (Pl. Syst. Evol. 168, 195-219, 1989; 177, 213-219, 1991).