Genus: Highly flattened; pellicle firm; body form constant (Kudo, 1966). Chloroplasts small, discoid, pyrenoids usually absent; most species flat and leaf-shaped; often with ridges or fins running helically or longitudinally (Illustrated Guide, 1985). Species: Cell body 37-68 μm long, 25-45 μm wide, dorsally broad ovoidal, cauda relatively long and curved, striae straight, a longitudinal prominent ridge at the center which makes frontal view triangular; a locomotive flagellum nearly the same as the cell body in length; paramylon bodies large disc-shaped, 1-2 in number (An Illustrated Guide to Freshwater Zooplankton in Japan, 2000).

Similar species -- >> P. pleuronectes;

31 μm 63 μm 94 μm; x 640

Phacus curvicauda Swirenko: Cell body 24-26 μm diam., (25)-38-30 μm long; 2 paramylons (Illustrations of The Japanese Fresh-water Algae, 1977).