Chrysodidymus synuroideus, the only recognized species, is found in acidic bogs and similar freshwater environments.

Living two-celled colony showing flagella. Bright-field image.

The cells usually are found in pairs, interpreted as two-celled colonies. The cells of the pair form a linear array and are joined at their posterior ends. Cell shape ranges from ovate ("egg-shaped") to narrowly ellipsoidal ("football-shaped" [the American-style or "gridiron" football, for the non-Yanks in the audience]), or vaselike. Cell length is usually within the 5 - 10 micrometer range.

Each cell has two flagella of unequal length at the anterior end. The swimming behavior mediated by these flagella consists of moving back and forth for short distances along the longitudinal axis formed by the two cells. This behavior is diagnostic; two-celled colonies of other species usually tumble when they attempt to swim.

Each cell has one, centrally-located nucleus and, usually, two plate-like, peripheral ("parietal"), golden-colored chloroplasts that do not contain pyrenoids. Cells in stationary phase may develop a reddish pigmentation that masks the golden color of the chloroplast pigments.

A large vacuole at the posterior end of each cell is presumed to contain chrysolaminarin, the beta-linked polyglucan that is the principal storage polysaccharide of most golden algae.

The scales on the cell bodies, and the scales and hairs present on the flagella, are not visible under the light microscope. For details on these structures, see the Ultrastructure section.

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