[General] Elongate thickenings on the shell-wall, spicules, cornets, etc. When strongly developed they are usually termed keels or wings.

[Radiolaria Polycystina] In Nassellaria: elongated, usually unperforated thickenings in the shell-wall. Sometimes the ribs can extend into wings (shell structure 4) or feet (shell structure 3). Dorsal and primary lateral spines embedded in the wall of the thorax can also form ribs.