Note that we deem cilium and microtubule-based flagellum to be equivalent. In most eukaryotic species, intracellular sub-components of the cilium, such as the ciliary base and rootlet, are located near the plasma membrane. In Diplomonads such as Giardia, instead, the same ciliary parts are located further intracellularly. Also, 'cilium' may be used when axonemal structure and/or motility are unknown, or when axonemal structure is unusual. For all other cases, please refer to children of 'cilium'. Finally, note that any role of ciliary proteins in sensory events should be captured by annotating to relevant biological process terms.