Genus: Solitary or colonial; body surface delicate; one to two chloroplasts; usually with a stigma; fresh water (Kudo, 1966). One to several chloroplasts; pyrenoid and/or eyespot (stigma) in some; cells naked, globular, ellipsoidal or pyriform (Illustrated Guide, 1985). Species:

20 μm 40 μm 60 μm; x 1000

Images of collecting locality: Rice field, Shibasaki, Nagareyama city, Chiba Pref., Japan, February 11, 2008 by Y. Tsukii

O. mutabilis Klebs: Ovoid to spherical; plastic; 15-30 μm long, 8-22 μm wide (Kudo, 1966). Resembles Chromulina; 1-2 chloroplasts; usually a stigma (How to know the protozoa, 1979).

O. granularis Doflein: 5-12 μm long; no stigma (Kudo, 1966).