Cilium- and flagellum-specific protein that plays a role in axonemal structure organization and motility. Involved in the regulation of the size and morphology of cilia. Required for axonemal microtubules polyglutamylation (By similarity). Plays a role in cilia stability (PubMed:24574454). Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme. Display curved body axis, short somite length and defective heart-looping orientation. Belongs to the CFAP20 family.