A basal body is the centriole-derived structure at the base of a cilium or a eukaryotic flagellum. It anchors and organizes the microtubules of the projecting structure. A typical basal body contains nine peripheral microtubule triplets; farther along the cilium, the corresponding outer elements usually continue as doublets. The central pair found in many motile cilia is not a pair of central microtubules running through the basal body.[ref]
Molecular Biology of the Cell, 4th edition by Bruce Alberts and others. Chapter 16, Cilia and Flagella: basal-body triplets and axonemal doublets
In a cell bearing a primary cilium, a mature centriole can dock at the cell membrane and act as its basal body. The same underlying organelle therefore has different roles depending on its position and associated structures: a centriole within a centrosome helps organize an intracellular microtubule system, whereas a basal body organizes a projection from the surface. The ninefold arrangement is connected to assembly of SAS-6 into a central cartwheel scaffold.[ref]
Structural basis of the 9-fold symmetry of centrioles by Daiju Kitagawa and others. Summary and structural model, Figures 5–6
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