Foramen

A foramen is the large, unoccluded opening in the external or internal wall of a loculate areola, opposite the velum (Ross et al. 1979 p. 527). From Latin for hole. Plural is foramina.

For instance, in Thalassiosira the foramina are on the outside of the areolae and in Coscinodiscus the foramina are on the inside of the areolae.

See also occlusion and alveolus for more examples and illustrations.

Citations

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.