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 65-240 μm long, 29-36 μm diam.; 1 chloroplast making 2.5-8 turns in each cell; conjugation scalariform; tubes formed from both gametangial cells; female gametangium cylindrical or slightly swelled; zygospores football-shaped (55-85 μm long, 30-36 μm wide) (Illustrations of The Japanese Fresh-water Algae, 1977).