A flexible whiplike intracellular extension of many eukaryotic cells, with a characteristic nine-fold symmetry, an arrangement of nine paired peripheral microtubules and one central pair, often termed 9 _ 2 symmetry; it appears to grow out from a basal body (kinetosome) in the cell and is a fundamental component of the eukaryotic cell. Both the cilium and the eukaryotic flagellum (not the bacterial flagellum which lacks the 9 _ 2 pattern) are considered undulipodium.
Origin: LL. Undulo, to move in waves, fr. L. Unda, wave, _ Mod.L. Podium, fr. G. Podion, dim. Of pous, foot