Family: Colonies of a fixed number of cells (4, 8, 16, 32, or more) arranged 2- or 3-dimensionally; cells spherical, ellipsoidal, polygonal, etc. in shape; chloroplasts 1 or several, plate-like in shape, with 1 pyrenoid; asexual reproduction by autocoenobium (Illustrations of The Japanese Fresh-water Algae, 1977).
Genus: Planktonic; colony of 4 cells; cell body spherical, covered with elongated spiny projections; cells attached with each other arranging cruciform on a plane, with a small space at the center of the colony; a single chloroplast plate-like, with a pyrenoid (Guide book to the "Photomicrographs of the Freshwater Algae", 1998).
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T. staurogeniaforme ?
cell 6 μm φ
Ueno
Tokyo, 2001
Tetrastrum sp.
cell 6 μm φ
Japan, 1998
Tetrastrum sp.
cell μm
Japan, 199?
T. heterocanthum
cell μm
Higusa-numa
Hikari
Chiba, 2003
T. heterocanthum
cell μm
O-ike park
Yabuki
Fukushima, 2003
T. heterocanthum
cell 7 x 7 μm
Yakebe-ike
Higashi-Murayama
Tokyo, 2006
