Flagellate
Flagellates are single-celleded protists with one or more flagella, whip-like organelles often used for propulsion. Originally they were grouped together as the class or phylum Mastigophora, but the different lines do not appear particularly closely related. These include:
It is quite possible the ancestral eukaryote was a flagellate, and if not they appeared fairly early on in their development. The animals, fungi, and plants are all derived from various lines of flagellates - something reflected in the presence of flagellate cells in most forms, whose ultrastructure is a useful guide to determining relationships.
