Hymen

A hymen is a very delicate, porous membrane of silica occluding an areola or an alveolus. It is visible only with electron microscopy. 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. The plural is hymenes.

In contrast, a cribrum is an occlusion with larger pores.

Hymenes are found in many raphid genera such as Cocconeis and Neidiopsis. In some raphid diatoms such as Navicula, a hymen forms the only occlusion of an areola, covering the inner opening. In others such as Diploneis, a hymen covers the inner opening of the areola and a cribrum covers the outer opening of the areolae.

See also cribrum and occlusion (a general term for covering).

Alternative Terms

rica: Used in some older literature (e.g., Ross et al., 1979).

Citations

Cox, E.J. (1999) Variation in patterns of valve morphogenesis between representatives of six biraphid diatom genera (Bacillariophyceae). Journal of Phycology 35: 1297-1312
Cox, E.J. (2004) Pore occlusions in raphid diatoms - a reassessment of their structure and terminology, with particular reference to members of the Cymbellales. Diatom 20: 33-46.

Publication Link: 10.11464/diatom1985.20.0_33
Idei M., Sato S. and Mann D.G. (2020) The Amazing World of Diatoms. Sogensha Publishers, Osaka, Japan, pp. 176.
Ross, R., Cox, E.J., Karayeva, N.I., Mann, D.G., Paddock, T.B.B., Simonsen, R. and Sims, P.A. (1979) An amended terminology for the siliceous components of the diatom cell Nova Hedwigia, Beihefte 64: 513-533
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.

Diploneis smithii - hymenes — Internal view of *Diploneis smithii* (TEM) showing areolae in two biseriate striae. Hymenes occlude the openings of the areolae and have pores ~ 9 nm in diameter. Visible through the hymenes are cribra occluding the outside openings of the areolae. Scale bar = 1 µm.

Hymenes Bahls2014 — Inside of a valve of *Neidiopsis hamiltonii* (SEM) showing two adjacent, parallel areolae. Each areola is covered on the inside by a hymen, which has closely spaced pores ~ 8 nm in diameter. Scale bar = 0.5 µm.