The taxonomy of green algae endosymbiotic in ciliates and a sponge

The taxonomy of coccoid chlorophycean algae living endosymbiotically in ciliates (Climacostomum virens Ehrenb., Euplotes daidaleos Diller et Kounaris, Paramecium bursaria Ehrenb., Stentor polymorphus (Müll.) Ehrenb.) and a sponge (Spongilla sp.) was studied by investigation of physiological and ultrastructural features. Algae isolated from different hosts are not identical but all belong to the genus Chlorella. They excrete mono- and disaccharides and thus differ principally from free-living Chlorella spp. Other features show them to be closely related to the Chlorella vulgaris group, e.g. Chlorella vulgaris Beij., Chlorella sorokiniana Shih. et Krauss, Chlorella saccharophila (Krüg.) Mig., and Chlorella lobophora, Andr. The taxonomic value of the term “Zoochlorella” is discussed. It is proposed to regard it as a nomen ambiguum and to replace it by the prefix “symbiotic” and the exact genus or species designation or in uncertain cases by “symbiotic green alga”.