Species: 45-100 μm long, 30-70 μm wide; short posterior prolongation slightly curved; a prominent ridge on the convex side; longitudinally striated; one ? circular paramylon (paramylum) body near center; flagellum as long as cell body (Kudo, 1966). Cell body nearly spherical at dorsal view; anterior end separated into two spherical projections; cauda strongly curved; dorsal ridge short or absent (cf. dorsal ridge present P. triqueter); cell body 40-80 μm long, 30-50 μm wide; two ? paramylon bodies disc-shaped; striae straight (An Illustrated Guide to Freshwater Zooplankton in Japan, 2000).