epitheca (plural epithecae)
- (microbiology, planktology) The upper half of the theca of a thecate protist such as a diatom or dinoflagellate.
- The frustule's structure is usually composed of two overlapping sections, known as valves. The upper valve is termed the epitheca and is slightly larger and overlaps the lower valve, the hypotheca.
- ucl.ac.uk diatom webpage
- The diatom frustule is often likened to a pill-box ... with an epitheca (larger upper valve), and a hypotheca (smaller lower valve).