These are the amebas. Many species are free living or commensal, but a few species are relatively benign but occasionally serious protozoan parasites of humans and domestic animals. Until recently they have been classified with the flagellated protozoans.
The parasitic species are primarily extracellular, direct life cycle parasites transmitted by ingestion of water contaminated by cysts.
Its members possess pseudopodia for locomotion. Flagella are restricted to developmental stages. There is just a single type of nucleus.