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: Colonies of 4 cells, arranging learly; cell body spindle-shaped, both ends slightly pointed, 10-22 μm long, 5-8 μm wide; each cell with longitudinal ridges on both sides (Illustrations of The Japanese Fresh-water Algae, 1977).

50 μm 100 μm 150 μm; x 400 : 31 μm 63 μm 94 μm; x 640

S. armatus (Chodat) G. M. Smith var. chodatii G. M. Smith: Colonies of 2, 4, 8 cells, arranging linearly; cell body ovoid or elongated ellipsoidal, both ends rounded, 7-14 μm long, 3-5 μm wide; each cells with longitudinal ridges on both sides, but ridges unclear at the center; outer cells with short spines (2-4 μm long) projecting inward (Illustrations of The Japanese Fresh-water Algae, 1977).