Examples of archaebacteria include the halophiles, the methanogens and the thermophiles. Arcahebacteria are unicellular organisms belonging to the domain Archaea. One characteristic they all have in common is the ability to thrive in extreme environmental conditions that existed several billion years ago.
The halophiles are found in conditions where salt content is high. This includes lakes and seawater. The methanogens produce methane and are found in the intestines of ruminants and in bogs and sewage treatment plants. Thermophiles are found in environments with intense heat, such as in springs and near hydrothermal vents. Archaebacteria are similar to eubacteria in that they lack a nucleus.