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 125-500 μm long, 125-150 μm diam., 3-8 chloroplasts making 0.4-5 turns in each cell (Illustrations of The Japanese Fresh-water Algae, 1977).