Authors: Finlay, B.J. and Esteban, G.F.
Protozoa are microscopic organisms. Each protozoon typically exists as a single, independent cell, and all free-living protozoa fit within the definition of phagotrophic microbial eukaryotes. This article describes the functional roles of protozoa, the nature of protozoan species, protozoa and ecosystem function, and the biological diversity and global species richness of the protozoa.