Frustules biraphid, valves narrow, linear or sigmoid, a narrow central sternum, raphe in a keel formed by the valve face and mantle positioned around the margin of the valves.
The narrow valves and construction of the keel are features used to separate this genus from Surirella. In the past Stenopterobia was understood to contain sigmoid species only (e.g. S. intermediate-- see Hustedt 1930), but more recent interpretations, based on electron microscopical observations (e.g. Round et al. 1990; Krammer and Lange-Bertalot 1991), include species with straight valves such as S. delicatissima in the genus.
Light Microscope Image(s)
Each image is accompanied by the genus and species, California Academy of Sciences slide number (ie. CAS 612010), location of the specimen on the slide, and dimension in microns.