Cells are united by their bases in two-celled colonies. They have an armour of siliceous scales, consisting of a perforated oval plate with a short apical spine. Two flagella of almost equal length are covered with small linear or clavate scales. The genus comprises single autotrophic species, C. synuroideus, found in freshwater habitats worldwide.

A. Chrysodidymus cell covered with armour of silica scales. B. Oval, perforated cell with a short apical spine.