Family: Colonies of a fixed number of cells or reticulated bag in shape; chloroplasts plate-like or reticulated, with one or many pyrenoids; asexual reproduction by zoospores, sexual reproduction by fertilization (Illustrations of The Japanese Fresh-water Algae, 1977).
Genus: Colonies of a fixed number of cells, flat, circular in shape; cell body polygonal in shape, with horn-like projections; cell wall garanulated, wrinkled or notched; chloroplasts plate-like or reticular; asexual reproduction by zoospore; sexual reproduction by isogametes (Illustrations of The Japanese Fresh-water Algae, 1977).

P. boryanum 1 clip Kurome river Asaka Saitama, 2000	P. tetras 1 clip Kurome river Asaka Saitama, 2000
P. duplex 1 clip μm Higashi-hiroshima Hiroshima, 1998	P. tetras 1 clip μm Higashi-hiroshima Hiroshima, 1998
P. tetras 1 clip μm Higashi-hiroshima Hiroshima, 1998	P. tetras 1 clip μm Higashi-hiroshima Hiroshima, 1998	P. tetras 1 clip 16 = 11 + 5 N/L=0.50 μm Higashi-hiroshima Hiroshima, 1998