Family: Colonies of fixed number of cells (4, 8, 16, 32, or more) arranged 2- or 3-dimensionally;
cells spherical, ellipsoidal, polygonal, etc. in shape; chloroplasts 1 or several, plate-like in shape,
with 1 pyrenoid; reproduction only by asexual autospores.
Genus: Colonies of 4 (or 2, 8, 16) cells attached side by side, arranged linearly or zigzag; cell body elliptical or spindle or crescent in shape; terminal cells with spiny projections in many species; cell wall usually smooth, but in some species granulated or dented or ridged (Illustrations of The Japanese Fresh-water Algae, 1977).
Scenedesmus circumfusus, Uruguay 1999, photo by Y. Tsukii