A pointed, silica extension of the valve, shorter than a seta. Spines and may be solid or hollow, very long or tiny, single or many, and they may arise from different points on 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.