Family: Small, less than 50 μm; oblong to ovate;
ridges faint or absent.
Genus: Body ovate in locomotion, longer than broad, with clear zone as anterior part;
uninucleate (Illustrated Guide, 1985).
Clydonella sp. (Schaeffer, 1926),
cell body 15 μm long, 17 μm wide, L/W=0.9,
x 640, Kurome river, Asaka city, Saitama Pref., Japan, January 9, 2005 by Y. Tsukii
94 μm; x 640