∞ generated and posted on 2016.08.26 ∞
Plasma-membrane enclosed cytoplasmic extensions that are relatively long and few in number per cell and which are used to push against the fluid found outside of the cell.
Flagella, singular, flagellum, are longer and whip like while cilia are shorter and oar like. Both cilia and flagella are found in free-living protists while only cilia tend to be found inside of animal bodies. Sponges along with sperm cells, though, employ flagella, and some algae employ biflagellated sperm cells.
Note that bacteria also often possess flagella though bacterial flagella are not related to the flagella of eukaryotic cells other than serving as a means by which cells push against water, that is, bacterial flagella are analogous to eukaryotic flagella rather than homologous.
The following video shows protists swimming and/or eating, including the ciliated protist type known as ciliates: