Protozoa (from the Greek words proton, meaning "first", and zoa, meaning "animals") is a subkingdom
of microorganism
that are classified generally as unicellular non-fungal eukarvotes. Protozoans are a major component of the ecosystem. The word
protozoan is originally an adjective and is used as a noun.While there is not any exact definition for the term
protozoan, most scientists use the word to refer to a unicellular heterotrophic protist, such as the amoeba and ciliate. The term
algae is used for microorganisms that photosynthesize. However, the distinction between protozoa and algae is often vague. For example, the algae
Dinobryon has chloroplasts for photosynthesis, but it can also feed on organic matter and is motile. Protozoans are referred to generally as animal-like protists.
The Protozoa are a paraphyletic
group (it does not include all genetic relatives of the group). They constitute their own "kingdom" by the Intregated Taxonomic Information System 2009 classification.
Over 30,000 different types of protozoa have been documented.
