Crenarchaeota has the distinction of including microbial species with the highest known growth temperatures of any organisms. Although they are microscopic, single-celled organisms, they flourish under conditions which would quickly kill most “higher” organisms. As a rule, they grow best between 80° and 100°C (100°C = 212°F, the boiling point of water at sea level), and several species will not grow below 80°C. Several species also prefer to live under very acidic conditions in dilute solutions of hot sulfuric acid. Approximately 15 genera are known, and most of the hyperthermophilic species have been isolated from marine or terrestrial volcanic environments, such as hot springs and shallow or deep-sea hydrothermal vents. Recent analyses of genetic sequences obtained directly from environomental samples, however, indicate the existence of low temperature Crenarchaeota, which have not yet been cultivated.