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 165-225 μm long, 15-17 μm diam., 1 chloroplast making 4-7 turns in each cell (Illustrations of The Japanese Fresh-water Algae, 1977).