The siliceous unit that lies at each end of the frustule. The two valves are linked by the girdle bands.

The morphology of the valve provides many of the features used to classify diatoms.

S Leptostauron Cruciform
Image Credit: Eduardo Morales
A scanning electron micrograph showing the intricate sculpturing of the outside of a valve of Staurosirella leptostauron. Spines project from the costae, lineolate areolae make up the striae, and minute structures compose the apical pore fields.