Group of bacteria whose members differ from the eubacteria in certain physical, physiological, and genetic features (e.g., cell-wall components).
Archaebacteria are aquatic or terrestrial microorganisms that exhibit a diversity of shapes, including spherical, rod-shaped, and spiral forms. They survive in various extreme environments, including very hot or salty ones. Some require oxygen; some do not. Some produce methane as an end product; others depend on sulfur for their metabolism.