Flagellum
Eukaryotic flagella – those of animal, plant, and protist cells – are complex cellular projections that lash back and forth.  Eukaryotic flagella are classed along with eukaryotic motile cilia as undulipodia to emphasize their distinctive wavy appendage role in cellular function or motility.  Primary cilia are immotile, and are not undulipodia; they have a structurally different 9+0 axoneme rather than the 9+2 axoneme found in both flagella and motile cilia undulopodia.