Family: Cell body cylindrical or spindle-shaped, loosely attached with each other to form a filamentous colony; cell wall smooth, consists of a single partition, one layer; 1-2 chloroplasts plate- or ribbon-like, with pyrenoids; a single nucleus centrally placed.
Genus: Cell body cylindroid or spindle in shape; spiral ribbon-like chloroplasts or laminae of the chloroplast arranged spirally around central rod (Illustrations of The Japanese Fresh-water Algae, 1977).

S. obscura 2 clips 72 x 13 μm Hiroshima, 1998