Protozoa

Abstract

Protozoa constitute a convenience group of eukaryotic microbes that are generally defined by their heterotrophism and unicellularity. Free-living protozoa are ubiquitous and found in planktonic, benthic, and soil biomes and a wide variety of protozoa are symbionts with several being important pathogens. The diversity of the protozoa encompasses nearly the entire diversity of eukaryotes since organisms that can be defined as protozoa are found in all major eukaryotic groups. Accordingly, the first eukaryote likely resembled a protozoan and phagotrophy played a major role in eukaryotic evolution, including the acquisition of phototrophy. Distinctions between organisms that were traditionally grouped as protozoa or algae often blurs when phylogeny is considered.