Genus: Cell body crescent in shape (long, curved, tapered at both ends); cross section rounded; cell wall smooth or with longitudinal lines, bands on the cell wall in some species; chloroplast laminae ridged and radially arranged, which makes cross section star-shaped; pyrenoids aligned or scattered (Illustrations of The Japanese Fresh-water Algae, 1977).
Species [var. setaceum]: Cell body small, thin, central region straight, spindle-shaped, elongated to and curved near both termini, 150-(252-528)-600 μm long, 6-(8.6-17) μm wide, L/W=30-33; cell wall transparent or slightly yellowish, finely striated (Illustrations of The Japanese Fresh-water Algae, 1977).