The members of Anisonema have two, heterodynamic flagella; unequal in length; both emergent from the canal; the shorter, thinner flagellum beats actively with a sweeping motion, is directed anteriorly and the longer one trails posteriorly and is up to three times the length of cell. The trailing flagellum forms a hook as it leaves the flagellar pocket and bends backward. This feature is not unique to the genus Anisonema and may be encountered in the genus Dinema and Ploeotia. Cells of Anisonema are slightly dorso-ventrally flattened with limited metabolic capacity and no visible mouth. Pellicle smooth or with fine ridges. Anisonema has a distinctive movement in which gliding is interrupted by sudden backward jerks. The genus Anisonema contains about 25 species. The most commonly reported species from freshwater and marine sites is Anisonema acinus.