Diatom

See also: Algae

Electron microscope photo of a 10-micron-long diatom, Achnanthidium minutissimum (Kützing) Czarnecki.

Diatoms are single-celled algae living in water, encased in tiny glass shells. They are the bottom of the food chain. The mix of their populations serves as a good indicator of the health of a body of water. Algae, including diatoms, account for nearly a quarter of the world's oxygen.