Glossary
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Theca
A theca is one half of a diatom frustule. A theca consists of a valve and one or more copulae. The larger valve and its copulae are termed the epitheca, while the smaller valve and its copulae are termed the hypotheca. In Latin theca means a sheath, case, or box.
See also copula, valve, and frustule.
Image Credit: Adapted from Round et al. 1990
Image Credit: Adapted from Round et al. 1990
A frustule is composed of two valves and its component parts, termed epitheca and hypotheca.