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.