Order: Uninucleate filamentous algae without branching; cell body mostly cylindrical; all cells can divide; chloroplasts parietal with one or more pyrenoids; asexual reproduction by fragmentation of algae or formation of zoospores with two or four flagella; usually eyespot present; sexual reproduction by isogamy, anisogamy or oogamy
Family: Chloroplasts plate-like or ribbon-like; sexual reproduction by isogamy.
Genus: Filamentous algae without branching, no rhizoids, covered with gelatinous sheath; cell body cylindrical or ellipsoidal, cells attached side by side or separated; a single chloroplast band-form, with a pyrenoid (Guide book to the "Photomicrographs of the Freshwater Algae", 1998).

Geminella sp. 7 clips 5-12 x 11 μm Karasugamori Nishinasuno Tochigi, 2001

Geminella sp. 4 clips 5-12 x 11 μm Karasugamori Nishinasuno Tochigi, 2001