cilium motile cilium GO:0009434 motile primary cilium A cilium which may have a variable arrangement of axonemal microtubules and also contains molecular motors. It may beat with a whip-like pattern that promotes cell motility or transport of fluids and other cells across a cell surface, such as on epithelial cells that line the lumenal ducts of various tissues; or they may display a distinct twirling motion that directs fluid flow asymmetrically across the cellular surface to affect asymmetric body plan organization. Motile cilia can be found in single as well as multiple copies per cell. microtubule-based flagellum nodal cilium motile primary cilia GO:0031514 motile secondary cilium motile cilia GO:0031512