Cilium- and flagellum-specific protein that plays a role in axonemal structure organization and motility (By similarity). Involved in the regulation of the size and morphology of cilia. Required for axonemal microtubules polyglutamylation (By similarity). Microtubule inner protein (MIP) part of the dynein-decorated doublet microtubules (DMTs) in cilia axoneme. Belongs to the CFAP20 family.