In some older systems of classification, Zoomastigophora is a phylum (more commonly known as zooflagellates) within the kingdom Protista. Organisms within this group have a spherical, elongated body with a single central nucleus. They are single-celled, heterotrophic eukaryotes and may form symbiotic relationships with other organisms, including Trichomonas.^[1] Some species are parasitic, causing diseases such as the African Sleeping Sickness, caused by the zooflagellate Trypanosoma brucei.^[2] Zooflagellates have one or more flagella but do not have plastids or cell walls.^[3]

A few are mutualistic, such as those that live in the guts of termites and aid the bacteria present in breaking down wood.^{[citation needed]}