The siliceous parts of the diatom cell wall. Composed of the larger
and the smaller
The epitheca overlaps the hypotheca similar to a pill box or Petri dish. From Latin for a little piece.
See also valve and cingulum.
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.
Image Credit: Ian Bishop
An SEM image of part of a frustule of Tabelllaria flocculosa. A valve, with its marginal spines, is visible at the bottom of the image. Attached to the valve are many of the copulae, or girdle bands, that make up the girdle.
Image Credit: Eduardo Morales
An SEM image of a complete frustule of Staurosirella pinnata, showing both valves and the entire girdle, or cincture, between them.