A very delicate, porous membrane of silica covering the opening of an areola or an alveolus. The pores of the hymen may be round or elongated and range from 5-10 nm (0.005-0.010 µm) in their shortest diameter. Found in many raphid genera such as Cocconeis and Neidiopsis. Visible only with the SEM. Plural form is hymenes.
A similar structure with larger pores, found in many centric and some raphid diatoms, is the cribrum.
Round, F.E., Crawford, R.M. and Mann, D.G. (1990). The Diatoms. Biology and Morphology of the Genera. Cambridge University Press, Cambridge, 747 pp.