Genus: Cigar- or foot-shaped; a single macronucleus and 1 to several vesicular or compact microuclei (Kudo, 1966). Species: Oblong; 50-105 (80-90) μm long; a compact micronucleus; two contractile vacuoles; fresh water (Kudo, 1966). Similar in shape to P. bursaria but much more rounded at both ends; 70-90 μm long; two conctractile vacuoles; a single ovoid macronucleus with a single micronucleus; caudal cilia present (Carey, 1992). Generally believed P. trichium = P. putrinum (see below)

50 μm 100 μm 150 μm; x 400

31 μm 63 μm 94 μm; x 640

P. putrinum Claparède and Lachmann, 1858: Similar to P. bursaria in shape; but single contractile vacuole; no symbiotic chlorella; 80-150 μm long; fresh water (Kudo, 1966).