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).
Species [ var. arumatus ]: Colonies of 2, 4, 8 cells arranging linearly or slightly sigzag; cell body ovoid or elongated ellipsoidal, both ends rounded, 10-20 μm long, 3.5-8 μm wide; each cell with longitudinal ridges on both sides, ridges distinct at both ends but unclear at the center; outer cells with spiny projections (8-15 μm long) at both ends
[ var. bicaudatus ]: Cell body 10-15 μm long, 2.5-5 μm wide; outer cells with a spiny projection only on one end (Illustrations of The Japanese Fresh-water Algae, 1977).