Organisms can vary in size, shape, and behavior. But do you know how much they can vary in size? Find out how small the smallest organism is.
The Smallest Living Organism
The smallest virus is the Porcine circovirus, a virus that infects pigs, with a diameter of 17 nm (a nanometer is a metric unit that is a billionth of a meter). Since many biologists do not believe viruses are living organisms, the smallest known organism would be the Nanoarchaeum equitans, a tiny Archaea (an organism similar to bacteria), at 400 nm. This organism was discovered in 2002 by Karl Stetter, a German microbiologist, in a hydrothermal vent near the Icelandic coast.
A Nanoarchaeum equitans (the two bottom right circles) and its host