Flagellate

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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:

Excavates (e.g. euglenids, kinetoplastids, Giardia, etc.)
Cercozoa
Ebriids
Ellobiopsids
Dinoflagellates
Haptophytes
Stramenopiles (golden algae, bicosoecids, etc)
Cryptomonads
Green algae
Choanoflagellates

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 by the presence of flagellate cells in most forms, whose ultrastructure is a useful guide to determining relationships.