Genus: Two chloroplasts plate-like or slightly spiralled; a nucleus centrally located between the chloroplasts; mostly unicells, filaments rare (Illustrations of The Japanese Fresh-water Algae, 1977). Species: Cell body constricted near the both ends, (68-160)-288 μm long, (7-8)-10.8 μm wide, L/W = 10-16, cell wall densely granulated (Illustrations of The Japanese Fresh-water Algae, 1977).

31 μm 63 μm 94 μm; x 640

Gonatozygon brebissonii de Bary, cell body 146 μm long, 8 μm wide, x 640, Azami-ike (pond), Norikura highland, Azumi, Matsumoto city (formerly Azumi village), Nagano Pref., Japan, June 8, 2006 by Y. Tsukii
31 μm 63 μm 94 μm; x 640

Cell body 263 μm long, 7 μm wide, x 400, x 640

Images of collecting locality: Azami-ike (pond), Norikura highland, Azumi, Matsumoto city (formerly Azumi village), Nagano Pref., Japan, June 8, 2006 by Y. Tsukii

* Gonatozygon brebissonii var. echinatum Krieger: cell body cylindrical 96-140 μm long, 5-(5.5-7.5) μm wide, L/W = 15-20, cell wall covered with many fine hairs, both ends slightly swelled (Illustrations of The Japanese Fresh-water Algae, 1977).

Gonatozygon brebissonii Wolle var. brebissonii: cell body cylindrical 177-(180)-300 μm long, 10.5-15-(15.5) μm wide, L/W = 12-20, cell wall covered with many hairly spines, both ends slightly swelled (Illustrations of The Japanese Fresh-water Algae, 1977).

Gonatozygon monotaenium de Bary: cell body cylindrical (74-145)-284 μm long, 7.5-(9)-11.5 μm wide, L/W = 10-25, cell wall with many granules, both ends slightly swelled (Illustrations of The Japanese Fresh-water Algae, 1977).