Protozoa are 1) microscopic, single-celled eukaryotic organisms. 2) they lack a cell wall, but some of them have an elastic "shell" known as a pellicle. 3) They are mostly naked, but some protozoa have a simple endoskeleton or exoskeleton. 4) They are mostly heterotrophs, meaning that they cannot make their food, so they consume other animals, plants, or dead organic matter. 5) Protozoa are found as free-living in different habitats such as freshwater and soils and also in symbiotic or parasitic relationships with other organisms.