Genus: Trichome without mucous sheath; straight, long, consisting of numerous cells (Illustrations of The Japanese Fresh-water Algae, 1977).
Species: Trichome straight or slightly curved, without constriction at cell-cell junction, 2-3 μm wide; cell-body length nearly the same as its width (Illustrations of The Japanese Fresh-water Algae, 1977).
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O. planctonica ?
2 x 2 μm φ
L/W=1.0
Numappara marsh
Kuroiso
Tochigi, 2003
O. planctonica ?
3-5 x 2 μm φ
L/W=
Senjo-ga-hara
Nikko
Tochigi, 2003
O. planctonica ?
x 2 μm φ
L/W=
Shishizuka
Tsuchiura
Ibaraki, 2003
O. planctonica ?
2-3 x 2 μm φ
L/W=1.0-1.5
Kurome river
Asaka
Saitama, 2004
O. planctonica ?
x 1.5-2 μm φ
L/W=
Koma river
Sakado
Saitama, 2003
