<Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (September 2017) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This section does not cite any sources . Please help improve this section by adding citations to reliable sources . Unsourced material may be challenged and removed . (September 2017) (Learn how and when to remove this template message) </Td> </Tr> <P> Most known extremophiles are microorganisms . The domain Archaea contains renowned examples, but extremophiles are present in numerous and diverse genetic lineages of bacteria and archaeans . Furthermore, it is erroneous to use the term extremophile to encompass all archaeans, as some are mesophilic . Neither are all extremophiles unicellular; protostome animals found in similar environments include the Pompeii worm, the psychrophilic Grylloblattidae (insects) and Antarctic krill (a crustacean). Many would also classify tardigrades (water bears) as extremophiles but while tardigrades can survive in extreme environments, they are not considered extremophiles because they are not adapted to live in these conditions . Their chances of dying increase the longer they are exposed to the extreme environment . </P> <P> There are many classes of extremophiles that range all around the globe, each corresponding to the way its environmental niche differs from mesophilic conditions . These classifications are not exclusive . Many extremophiles fall under multiple categories and are classified as polyextremophiles . For example, organisms living inside hot rocks deep under Earth's surface are thermophilic and barophilic such as Thermococcus barophilus . A polyextremophile living at the summit of a mountain in the Atacama Desert might be a radioresistant xerophile, a psychrophile, and an oligotroph . Polyextremophiles are well known for their ability to tolerate both high and low pH levels . </P>

Which domain includes organisms that require extreme environmental conditions for survival