part of part_of part of cellular_component cilium organelle part ciliary part Any constituent part of a cilium, a specialized eukaryotic organelle that consists of a filiform extrusion of the cell surface. Each cilium is bounded by an extrusion of the cytoplasmic (plasma) membrane, and contains a regular longitudinal array of microtubules, anchored basally in a centriole. cilial part cilium part flagellar part flagellum component flagellum part microtubule-based flagellum part cell projection part