Genus: Elongate, with a broad rounded or truncate posterior end during locomotion; highly plastic; 
delicate pellicle shows a fine striation; a free flagellum, long and conspicuous, tapers toward free 
end; a second flagellum adheres to the pellicle; a contractile vacuole, anterior, close to the reservoir 
(Kudo, 1966).  
Species: 
 
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P. trichophorum: 40-70 μm long (Kudo, 1966); 20-80 μm long (Illustrated Guide, 1985); 20-70 μm long (How to know the protozoa, 1979).