Genus: Highly flattened; pellicle firm; body form constant (Kudo, 1966). Chloroplasts small, discoid, pyrenoids usually absent; most species flat and leaf-shaped; often with ridges or fins running helically or longitudinally (Illustrated Guide, 1985).
Species: (An illustrated guide to freshwater zooplankton in Japan, 2000).

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P. trypanon 40 x 22 μm Mizuko Fujimi Saitama, 2003	P. trypanon 44 x 22 μm river bank Doman-green Park Saitama, 2003	P. trypanon 41-42 x 18-19 μm Shimo-muneoka Shiki Saitama, 2004	P. trypanon 45 x 18 μm kenko-fukushi m.p. Koshigaya Saitama, 2005
P. trypanon 39 x 19 μm Okubo Ryoke Akigase park Saitama, 2005	P. trypanon ? 43 x 21 μm Mitsumata-numa Kawagoe etc. Saitama, 2005	P. trypanon 50 x 30 μm Banpaku memorial p. Tsukuba Ibaraki, 2006	P. trypanon μm Ryugahara m.4 Yuri-Honjo Akita, 2008

Similar species -->> P. pyrum;

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