Epitheca and Hypotheca
Definition
The two halves of the frustule. The epitheca (larger) fits over the hypotheca (smaller) like a lid over a box. During cell division each daughter cell retains one half and builds a new opposing half, so average cell size decreases over generations until sexual reproduction resets it.
- Epitheca
- Larger half, fits over the hypotheca
- Hypotheca
- Smaller half, fits inside the epitheca
- Division effect
- Average cell size shrinks across generations
- Reset mechanism
- Sexual reproduction
Common questions
Why does diatom size decline matter for forensic diatom analysis?+
Since a population's size range shifts predictably between reproductive resets, size-frequency distribution in a water or sediment sample can support comparing a questioned sample's diatom assemblage against a reference site, alongside species composition.
How does the epitheca/hypotheca structure relate to species identification?+
The frustule's valve shape, ornamentation, and the epitheca-hypotheca fit are part of the morphological features used to key out diatom species under the microscope, independent of the size-reduction cycle itself.
Related terms
- Assemblage
- The full community of diatom taxa present in a sample. The relative frequencies and absolute counts of species in an assemblage reflect...
- Frustule
- The silica cell wall of a diatom, composed of two overlapping valves (epitheca and hypotheca). Frustules are taxonomically distinctive, chemically resistant to...
- Raphe
- A longitudinal slit or canal in the valve of certain pennate diatoms that allows cytoplasmic streaming and active gliding movement across surfaces....
- Sporopollenin vs Biogenic Silica
- Pollen and spore walls are made of sporopollenin (a highly resistant biopolymer). Diatom frustules are made of biogenic opaline silica (SiO2·nH2O), a...
- Valve and Girdle Band
- The valve is the flat face of each frustule half, carrying the species-specific pore patterns used for identification. The girdle band is...