 "Nanoarchaeum equitans" is a species of microbe 200 to 500 nm in diameter.It was discovered in 2002 in a hydrothermal vent off the coast of Iceland by Karl Stetter.A thermophile that grows in near-boiling temperatures, "Nanoarchaeum" appears to be an obligatory symbiont on the archaeon "Ignicoccus"; it must be in contact with the host organism to survive.