DIATOMS

Cyclotella
Centric

Epithemia
Pennate
DIATOMS: Microscopic photosynthetic organisms with siliceous secondary plant walls termed "frustules." Mostly 20 - 100 µm, and generally of two forms: pennate or centric. Marine and freshwater organisms of various ecological preferences -- planktonic, benthic, etc. Diatoms are destroyed by hydrofluoric acid so they are never present in routine palynological preparations, and diatom processing involves treatment with strong oxidizing agents, which destroys pollen.