Archebacteria have been many times classified with bacteria because of all fundamental similarities. Archaebacteria contain two sub-groups:
(1) Methanogens and (2) Thermoacidophiles
Methanogens are strict anaerobe which produce methane from carbon dioxide or formic acid. Thats why these are called methane producers or methanogens.
Thermo-acidophiles are found in hot sulphur springs. Under aerobic conditions and at a temperature around 80 degree centigrate, these oxidise sulphur to sulphuric acid and can make the enviroment highly acidic.
Archaebacteria can survive in the absence of oxygen. Some archaebacteria are halophiles or salt loving and can live in strong solutions.