noun, singular: protozoon
In a five-kingdom scheme of classifying organisms, they belong to a taxonomic group within Kingdom Protista, and typically divided on the basis of their means of locomotion: Flagellates (e.g. Giardia lambdia), Amoeboids (e.g. Entamoeba histolytica), Sporozoans (e.g. Plasmodium knowlesi), Apicomplexa, Myxozoa, Microsporidia, and Ciliates (e.g. Balantidium coli).
Word origin: from Greek protohi = first and zoa = animals
Related forms: protozoan (noun or adjective), protozoic (adjective).
See also: protista.