[Radiolaria Polycystina] In Nassellaria: free portion of the apical spine (main spines/skeleton) in the cephalis.

[Pteropoda] The axis of the coiled shell of the Limacinidae to which the columellar muscle is attached and that also forms the inner aperture border where a thin membrane, the columellar membrane, is formed in some species (Limacina in oral view ; Peraclis in oral view ).