Occlusion

An occlusion is a porous layer of silica partially or completely covering an areola. The layer of silica can be a delicate membrane or a thicker plate. Occlusions are often useful for distinguishing groups of diatoms. Electron microscopy is usually needed to resolve the structure.

Seven types in two groups are included in this glossary.

1. hymen - pores < 15 nm

2. velum - pores > 15 nm
a. cribrum - pores > 30 nm
b. rota - bar across the areola
c. vola - projection extending from wall
d. foricula - wide attachment
e. tectulum - attached by small struts

See the glossary entry for each type.

Citations

Anonymous (1975) Proposals for standardization of diatom terminology and diagnoses Nova Hedwigia, Beihefte 53: 323-354
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
Cox, E.J. (2012) Ontogeny, homology, and terminology - wall morphogenesis as an aid to character recognition and character state definition for pennate diatom systematics Journal of Phycology 48: 1–31

Publication Link: 10.1111/j.1529-8817.2011.01081.x
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.