An order of the *Chlorophyceae
containing nonflagellate unicellular (e.g. Chlorella), colonial (e.g. Scenedesmus), coenobial (e.g. Pedias-trum), and coenocytic coenobial (e.g. Hydrodictyon) algae. Motility is restricted to the gametes and zoospores. Sexual reproduction is isogamous or anisogamous but never, so far as is known, oogamous. Asexual reproduction is by motile zoospores or nonmotile aplanospores (autospores).