Order: Filamentous algae without branching; cell body mostly cylindrical.
Family: Chloroplasts plate-like or ribbon-like; sexual reproduction by isogamy.
Genus: Filaments without gelatinous sheath, consisting of up to 20 cells; without rhizoids; (Illustrations of the Japanese Freshwater Algae, 1977).
Google Image Search
P. lauterborni
P. lauterbornii ?
8.5 x 3 μm
Omiya
Saitama, 2001