Genus: Filament without branching; cell body cylindrical; one or several chloroplasts band-shaped, spirally arranged within the cell, pyrenoids present; septum with or without folded structure (Guide book to the "Photomicrographs of the Freshwater Algae", 1998). About 300 species (Illustrations of The Japanese Fresh-water Algae, 1977).
Species: Vegetative cells 30-70 μm long, 30-38 μm wide; a single chloroplast making 1-4 turns in each cell; conjugation scalariform; female gametangium swelled toward male gametangium; zygospores ellipsoidal or broad ellipsoidal or spherical in shape (45-65 μm long, 30-35 μm wide) (Illustrations of The Japanese Fresh-water Algae, 1977).