An extremophile is any microbe that thrives in extreme conditions of temperature, pressure, salinity, or concentrations of hostile chemicals. Many extremophiles belong to the kingdom Archaea, also known as Archaebacteria, and most known Archaebacteria are extremophiles. There are also extremophiles to be found outside the kingdom Archaea; for example there are bacteria and eukaryotic prokaryotes that are extremophiles, as well as species of worm, crustacean, and krill.
