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: Cell body 23-40 μm long, 20-30 μm wide, dorsal view nearly spherical; cauda short V-shaped and slightly curved or straight, striae also straight; a locomotive flagellum nearly the same as the cell body in length; paramylon bodies disc-shaped with a hole at the center, 1-2 in number; (An Illustrated Guide to Freshwater Zooplankton in Japan, 2000).

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Tail slightly curved
P. acuminatus μm Iyari marsh Omachi Nagano, 2008	P. acuminatus 45 x 34 μm Numa-no-hara m. Madarao highland Niigata, 2006	P. acuminatus paramylon with a hole 35 x 27 μm Kawashima or Kawajima Saitama, 2002	P. acuminatus paramylon with a hole 33 x 27 μm Sayama Saitama, 2001
P. acuminatus 33 x 28 μm Japan, 1998	P. acuminatus 36 x 30 μm near City Hall Fujimi Saitama, 2004	P. acuminatus μm Shimotsuma Ibaraki, 2003	P. acuminatus 39 x 30 μm near Town Hall Shobu Saitama, 2004
P. acuminatus μm Mizuko Fujimi Saitama, 2003	P. acuminatus ?? cell ellipsoidal 35 x 29 μm Akigase Park Saitama, 2002
Tail very short, not curved (V-shaped), slightly slanted
Cell body disc-shaped
var. acuminatus 26 x 22 μm Uruguay, 1999	P. acuminatus 31 x 27 μm Hiroshima, 1998 Movies	P. acuminatus 31 x 25 μm Shiba river near Owada Park Saitama, 2005	P. acuminatus 27 x 22 μm Musashi-Urawa Saitama, 2001
P. acuminatus 30 x 22 μm Higashi-sano Hakuba Nagano, 2004	P. acuminatus 28 x 22 μm Yamagata, 1999	P. acuminatus μm Okubo-cho Ashikaga Tochigi, 2003	P. acuminatus 26 x 21 μm Furuyakami Kawagoe Saitama, 2004
P. acuminatus μm Daidarabotchi-ike Iizuna-kogen Nagano, 2003	P. acuminatus ? 38 x 28 μm long. groove ? near Town Hall Shobu Saitama, 2004
Cell body ellipsoidal
var. iowensis 45 x 26 μm Kugedo Kawagoe Saitama, 2005	var. iowensis 34 x 19 μm Shiba river near Owada Park Saitama, 2005	var. iowensis 34 x 20 μm Akasaka-numa Hasuda Saitama, 2006	var. iowensis 35 x 21 μm Oura central p. Oura Gunma, 2006
var. iowensis 27 x 17 μm Musashi-Urawa Saitama, 2001
var. iowensis μm Ishinazaka Furukawa Miyagi, 2003	var. iowensis μm near railway st. Shimotsuma Ibaraki, 2003	var. iowensis 31 x 21 μm Shiba river near Owada Park Saitama, 2005	var. iowensis μm near Nan-ko Shirakawa Fukushima, 2003
var. iowensis μm Naruto Chiba, 2003	var. iowensis 29 x 20 μm Akao Sakado Saitama, 2004	var. iowensis 25 x 17 μm Iwajuku Gunma, 2001	var. iowensis paramylon with a hole 28 x 18 μm flag. 43 μm Mihashi Park Saitama, 2002
var. iowensis paramylon with a hole 27 x 17 μm Mizuko-kaizuka p. Fujimi Saitama, 2004	var. iowensis paramylon with a hole 25 x 17 μm Okubo Ryoke Akigase park Saitama, 2005	var. iowensis ? or v. acuminatus ? μm Maihara Shiga, 2003	var. iowensis or P. pusillus ? μm Senjo-ga-hara Nikko Tochigi, 2003
Posterior wider than anterior
P. acuminatus paramylon with a hole 34 x 22 μm Mizumoto Park Tokyo, 2001	P. acuminatus μm Higusa-numa Hikari Chiba, 2003	P. acuminatus paramylon with a hole 34 x 33 μm Ukima Park Tokyo, 2001	P. acuminatus paramylon with a hole 28 x 20 μm flag. 40 μm Mihashi Park Saitama, 2002
P. acuminatus paramylon with a hole μm flag. μm river bank Doman-green Park Saitama, 2003	P. acuminatus paramylon with a hole μm flag. μm Motono Chiba, 2003
???
P. acuminatus ? or P. brevicauda ? 33 x 26 μm Ukima Park Tokyo, 2001	P. acuminatus ? 27 x 18 μm Sakitama-kofun p. Gyoda Saitama, 2004

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