Paramecium caudatum is a common protist that inhabits a variety of aquatic ecosystems.

Paramecium are characterized by having two nuclei (a large macro and smaller micronucleus). They feed on bacteria and other microscopic organisms. Paramecium are a common food source for other protozoa such as Didinium and Chaos.

They are covered with tiny "hair-like" organelles called cilia. These cilia are used in both feeding and locomotion.