undulipodium

An undulipodium or 9+2 organelle is an intracellular projection of a eukaryotic cell containing a microtubule array.

The eukaryotic flagellum, also called a cilium or undulipodium, is structurally and evolutionarily distinct from prokaryotic flagella.

It is found at the base of a eukaryotic undulipodium (cilium or flagellum) and serves as a nucleation site for the growth of the axoneme microtubules.