A thin, domed, porous plate of silica covering the internal opening of an areola, found in genera such as Thalassiosira and Stephanodiscus. A cribrum is a type of velum. Visible only with the SEM. Plural form is cribra.

A similar structure with finer pores, found in many raphid diatoms, is the hymen.

Alternative Term

sieve plate



Ross, R. and Sims, P. (1972). The fine structure of the frustule in centric diatoms: a suggested terminology. British Phycological Journal 7: 139-163.

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.