More or less bean-shaped cells with two unequal flagella inserted in the lateral invagination, shorter flagellum directed anteriorly during swimming, the longer trailing; with a single plate-like chloroplast; pyrenoid; eyespot; reshwater species with a contractile vacuole; cells covered with up to 7 types of scales: the flagella with an basal layer of square scales overlain by pairs of rod-shaped scales and in some species by small stellate ones and 2 opposite rows of hair-shaped scales; sexual reproduction reported in one species; widespread ndistribution.