Methanogens, Halophiles, and Thermoacidophiles are found in the Archaea kingdom. They once believed to be a form of bacteria, but are no longer classified as bacteria. They live in extreme environments and are stll sometimes classified under archaebacteria. They are thought to be the oldest form of life found on earth.
Halophiles are found in environments with a high salt count. They change their structure in order to survive.
Thermoacidophiles like it acidic and hot.
Methanogens live in anerobic environments such as swamps where muck abounds. They thrive off of conditions that other bacteria would not be able to live in.