Genus: Cingulum (horizontal groove) located at the center of the body
(Illustrations of The Japanese Fresh-water Algae, 1977).
Cingulum more or less median; sulcus straight (Illrustrated Guide, 1985).
Gymnodinium ordinatum Skuja 1939 ?,
cell body 13 μm long, 10 μm wide,
x 640, Senjo-ga-hara (marsh), Nikko city, Tochigi Pref., Japan, September 2003 by Y. Tsukii
150 μm; x 400