Peridinium willei is a species of Dinoflagellata in the family Peridiniaceae. It has been called perennial.
It is found in the United States, Sweden, Norway, Brazil, and the Netherlands. P. willei lives in fresh water with one study saying it less likely occurs in lakes above 12 degrees or below 4 degrees.
Protozoa (sg.: protozoan or protozoon; alternative plural: protozoans) are a polyphyletic group of single-celled eukaryotes, either free-living or parasitic, that feed on organic matter such as other microorganisms or organic debris. Historically, protozoans were regarded as "one-celled animals".
When first introduced by Georg Goldfuss, in 1818, the taxon Protozoa was erected as a class within the Animalia, with the word 'protozoa' meaning "first animals", because they often possess animal-like behaviours, such as motility and predation, and lack a cell wall, as found in plants and many algae.