Nanoarchaeum equitans

Nanoarchaeum equitans is a species of marine archaea discovered in 2002 by Karl Stetter in a hydrothermal vent off the coast of Iceland on the Kolbeinsey Ridge. It has been proposed as the first species of a new phylum and is the only species in the genus Nanoarchaeum; strains have also been found on the sub-polar mid-oceanic ridge and in the Obsidian Pool of Yellowstone National Park. It grows best near boiling temperatures of about 80 degrees Celsius, at a pH of 6 and a salinity of 2 percent, making it a thermophile. Nanoarchaeum equitans is an obligate symbiont of the archaeon Ignicoccus, unable to synthesize its own lipids and dependent on contact with its host to survive; at only 400 nanometers in diameter, it is the smallest known archaeon.