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: 80-100 μm; similar to P. longicauda; twisted 40-60 degree (How to know the protozoa, 1979). Var. tortuosa: twisted about 90 degree.

31 μm 63 μm 94 μm; x 640

Images of collecting locality: Ko-numa (pond/marsh), Minakami town (formerly Tsukiyono town), Gunma Pref., Japan, April 15, 2007 by Y. Tsukii