Genus: Unicellular; planktonic; cell body elongated cylindroid, curved or twisted; both ends rounded, with spiny projections; cell wall not separated into two parts (compare to Centritractus); several chloroplasts plate-like, without pyrenoids (Guide book to the "Photomicrographs of the Freshwater Algae", 1998).
Species: Cell body cylindrical, curved, without projections at both ends, 5-6 μm in diam., 50-100 μm long (Illustrations of Japanese fresh-water algae, 1977).
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Similar genus -->> Centritractus
O. parvulum
x 7 μm
Akigase Park
Saitama, 2002
O. parvulum
μm
Omine-numa
Tsukiyono
Gunma, 2003
O. parvulum
μm
Kejo-numa
Furukawa
Miyagi, 2003
O. parvulum
155 x 6.5 μm
Watarase Wetland
Fujioka
Tochigi, 2005
O. parvulum ?
117 x 7-8.5 μm
Minuma-no-numa
Omiya daisan p.
Saitama, 2005
O. parvulum
70 x 7 μm
Okubo Ryoke
Akigase park
Saitama, 2005
O. parvulum
60 x 5 μm
near Akai wetland
Aizuwakamatsu
Fukushima, 2005
O. parvulum
x 5 μm
near Karakemi marsh
Omachi
Nagano, 2005
O. parvulum
70 x 5 μm
Ichinose-enchi
Norikura highland
Nagano, 2005
O. parvulum
195 x 5 μm
Shijuhachi-ike
Shiga highland
Nagano, 2005
O. parvulum
110 x 6 μm
Azami-ike
Norikura highland
Nagano, 2006
O. parvulum
115 x 9 μm
Tane-ike
Togakushi highland
Nagano, 2006