 
 
|  Genus: Cell body long, contractile; posterior end pointed or rounded; 
in gelatinous matrix (Kudo, 1966). Species: | 
 50 μm
 50 μm
 100 μm
 100 μm
 150 μm; x 400 :
 150 μm; x 400 : 
 31 μm
 31 μm
 63 μm
 63 μm
 94 μm; x 640
 94 μm; x 640
 
 
 
 
 
 
 
 
 
 
 
O. sessile Kent 1881: Fully extended body up to 300 μm long; colorless or slightly brownish; colony up to 5 x 3 mm; freshwater (Kudo, 1966).
O. vernalis (Stokes): Fully extended body up to 250 μm long; highly contractile; freshwater (Kudo, 1966).
O. ectatum Mast: 
Fully extended body up to 225-400 μm long; 
with many chlorellae; colony up to 3 mm in diam.; freshwater 
(Kudo, 1966).
O. vernale (Stokes): Cell body 250 μm long (Kahl, 1930).
O. versatile O.F. Müller, 1786: Fully extended body up to 300-600 μm long; with many chlorellae; colony up to 10 mm in diam. within gelatinous matrix; macronucleus band-form; contractile vacuole central with a canal connected to cytosotme; freshwater (Kojima et al., 1995).