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Chlamydomonas (division Chlorophyta) A genus of unicellular green algae in which each cell contains a single nucleus and a chloroplast the shape of which varies with species. The cell may be motile or nonmotile according to conditions of growth: motile cells have a pair of similar flagella at one end. There are many species. They are widely distributed and common, found in almost all types of aquatic environment and on moist soil. C. nivalis can grow on snow in mountains in N. America, the masses of cells giving rise to a reddish coloration known as ‘red snow’. (Chlamydomonas is sometimes classified as a genus of protozoa in the class Phytomastigophora.)