Colonies ellipsoidal to spherical, mostly of 8 or 16 cells of similar size, arranged in a common gelatinous matrix; colonial boundary smooth, part of it penetrating between cells into central region of colony forming individual sheaths around cells cells mostly closely packed, flattened by mutual compression and contiguous in the centre (any intercellular connections resulting from incomplete cleavage); cells obovate or wedge-shaped or more rounded, bearing 2 equal flagella; chloroplast cup-shaped, sometimes longitudinally striated, with one to several pyrenoids; eyespot present, larger in anterior cells; nucleus central; contractile vacuoles 2, anterior; asexual reproduction by formation of 8- or 16-celled plakea which inverts to form a spheroidal daughter colony; sexual reproduction isogamous or anisogamous, heterothallic or rarely homothallic; the constitutive cells of the colony escaping from the gelatinous matrix and functioning as gametes; gametes fuse to form a 4-flagellated planozygote, motile for some time; resting zygote spherical, mostly smooth-walled (one species with spinous wall), often with reddish contents; on germination, one or two biflagellate gone cells escaping from zygote wall and dividing into a gone colony; nutrition phototrophic or photo-organotrophic; common genus in freshwater, especially in pools and ditches and often appearing in cultures from dried soil samples.