Family: Unicells; cell body spherical or broad ellipsoidal; chloroplasts 1 to several in number, cup-shaped or plate-like, reticulated or star-shaped; with or without pyrenoids; reproduction by autospores and zoospores; many species found in soil (Illustrations of The Japanese Fresh-water Algae, 1977).
Genus: Unicellular or colonial within a gelatinous sheath; planktonic; cell body spherical; 1 or several chloroplasts cup-shaped, with a pyrenoid (Guide book to the "Photomicrographs of the Freshwater Algae", 1998).

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Planktosphaeria sp. cell μm φ Kanayama G.P. Kiyose Tokyo, 2003	Planktosphaeria sp. cell μm φ Shishizuka Tsuchiura Ibaraki, 2003	Planktosphaeria sp. cell μm φ Showa-machi g.p. Showa Saitama, 2003	Planktosphaeria sp. cell μm φ Omine-numa Tsukiyono Gunma, 2003
Planktosphaeria sp. cell 8-10 μm φ near Tama river Fuchu Tokyo, 2004	Planktosphaeria sp. cell 11 μm φ Koma river Sakado Saitama, 2003	Planktosphaeria sp. cell 9-20 μm φ Imou bog Toyohashi Aichi, 2004	Planktosphaeria sp. cell μm φ Mizuko Fujimi Saitama, 2003
Planktosphaeria sp. ? cell μm φ O-ike park Yabuki Fukushima, 2003	Planktosphaeria sp. ? cell μm φ Miyadera Iruma Saitama, 2003	Planktosphaeria sp. ? cell μm φ Kami-terayama Saitama Tochigi, 2004	Planktosphaeria sp. or Trebouxia ? cell 9-20 μm φ Furu-tone river Kasukabe Saitama, 2004
Planktosphaeria sp. cell 6-11 μm φ Aquatic botanical g. Sawara Chiba, 2004	Planktosphaeria sp. cell 4-61 μm φ near Yamaguchi Univ. Yamaguchi, 2004

Similar genus --> Dictyosphaerium

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