A non-motile cilium where the axoneme has a ring of nine outer microtubule doublets but no central microtubules (and is therefore called a 9+0 axoneme).
Source:
GOC:cilia,
PMID:22118931
Comment
This type of cilia may be present in solitary (authentic primary cilia in many cell types) or in multiple copies (e.g. in Grueneberg ganglion neurons).