Genus: Colonies of 4-32 cells; cell body long crescent or spindle in shape, tapered at both ends;
cells attached with each other at the center of the body, paralleled or radially arranged;
no gelatinous sheath; a chloroplast; no pyrenoids; planktonic
(Guide book to the "Photomicrographs of the Freshwater Algae", 1998).
Species: Cell body needle-shaped, tapered to the sharply pointed ends, spirally twisted or curved, 35-48 μm long, 1-2 μm wide; daughter cells culstered around one another in the middle twisted part of the cells; a single chloroplast parietal, plate-like, usually filling the cell, without pyrenoids (Photomicrographs of the Freshwater Algae, 1987).
* Ankistrodesmus falcatus (Corda) Ralfs: 25-30 μm long, 2-3 μm wide (Illustrations of The Japanese Fresh-water Algae, 1977).
Ankistrodesmus gracilis (Reinsch) Korshikov (Syn: Selenastrum gracile Reinsch): A colony of 8-32 cells, cells crescent in shape, 10-15 μm long, 3-5 μm wide, a single flattened chloroplast and a pyrenoid (Illustrations of The Japanese Fresh-water Algae, 1977).