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).

C. setaceum 2 clips 295 μm L/W=37 Japan, 1998