Spine
Diatoms have many different types of spines. "Spine" is a general term for a pointed silica extending from the valve. Spines may be solid or hollow, very long or tiny, single or many and they may arise from different points of the valve in different taxa.
Image Credit: Marina Potapova and Sarah Spaulding
Valves of Stephanodicus have many marginal spines. The spines are solid, rather than hollow.
Image Credit: Eduardo Morales
Staurosirella has hollow spines that are positioned in the costae, or thickened silica ridges, of the valve. These spines are hollow and forked at the tip.
Image Credit: Mark Edlund
Setae is a more specialized term, but could also be applied to the long spines of Chaetoceros elmorei are considered to aid in maintaining bouyancy in this planktonic species.