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: About 30-50 μm long, 10-20 μm wide; circular in cross section; with caudal prolongation; pelicle obliquely ridged; flagellum as long as the body (Kudo, 19660). Cell body 28-55 μm long, 10-21 μm wide, two paramylons thick disc-shaped, parietal (An Illustrated Guide to Freshwater Zooplankton in Japan, 2000).

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P. pyrum 50 x 17 μm Tonbo-no-numa Isumi Chiba, 2007	P. pyrum 48 x 20 μm water reservoir near Yamaguchi Univ. Yamaguchi, 2004	P. pyrum 45 x 18 μm Furu-tone river Kasukabe Saitama, 2004	P. pyrum ? or P. trypanon ? 43 x 17 μm Izumi 741 Namegawa Saitama, 2004
P. pyrum 42 x 18 μm Akao Sakado Saitama, 2004	P. pyrum 42 μm tail 17 μm Naruto Chiba, 2003	P. pyrum flat body 41 x 20 μm Akigase Park Saitama, 2002	P. pyrum 40 x 17 μm Japan, 1998 Movies
P. pyrum 40 μm tail 15 μm Hazama marsh Ashikaga Tochigi, 2003	P. pyrum 40 x 14 μm Kashiwa v.m.p. Kashiwa Chiba, 2008
P. pyrum 38 x 15 μm Sakitama-kofun p. Gyoda Saitama, 2004	P. pyrum 38 x 13 μm Imori pond Myoko highland Niigata, 2004	P. pyrum 37 x 16 μm Shiba river near Owada Park Saitama, 2005	P. pyrum 35 x 16 μm Chiba, 2001
P. pyrum 35 x 15 μm Higashi-sano Hakuba Nagano, 2004	P. pyrum 35 μm tail 13 μm Kodama Saitama, 2003	P. pyrum flat body 35 x 17 μm kenko-fukushi m.p. Koshigaya Saitama, 2005	P. pyrum flat body 33 x 14 μm Higashi-sano Hakuba Nagano, 2004
P. pyrum 32 μm tail 10 μm Senjo-ga-hara Nikko Tochigi, 2003	P. pyrum 31 x 14 μm Shiba river near Owada Park Saitama, 2005	P. pyrum 30 x 18 μm Mihashi Park Saitama, 2002	P. pyrum 20 x 12 μm Mihashi Park Saitama, 2006
P. pyrum or P. trypanon ? flat body 29 x 13 μm Saitama, 1999	P. pyrum 23 x 12 μm tail 10 μm Tsuchiura Ibaraki, 2002	P. pyrum 40 x 17 μm Tane-ike Togakushi highland Nagano, 2005	P. pyrum 39 x 15 μm Hanyu-Suigo p. Hanyu Saitama, 2006
P. pyrum 38 x 15 μm Hasu-ike Mizumoto Tokyo, 2006	P. pyrum 41 x 17 μm 35 x 15 μm Jionji-shinsui p. Iwatsuki-ku Saitama, 2006	P. pyrum 33 x 21 μm Kibagata p. Komatsu Ishikawa, 2007	P. pyrum or P. trypanon ? 33 μm tail 9 μm Shishizuka Tsuchiura Ibaraki, 2003

Similar species -->> P. trypanon;

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