Psychrophiles, halophiles, methanogens and thermophiles are all examples of Archaebacteria, according to the American Society for Microbiology. The University of California Museum of Paleontology defines Archaebacteria as members of the domain Archaea. Because organisms from this domain do not have the same genetic and biochemical makeup as bacteria, many scientists refer to them as Archaea instead of Archaebacteria.
Psychrophiles live in areas with extremely cold temperatures, notes the American Society for Microbiology. Psychrophiles are very hardy organisms because they are able to survive when their enzyme activity is suppressed or they have decreased membrane fluidity, according to a 2006 article in Embo reports. In contrast, thermophiles are able to survive at extremely high temperatures. Experts from the Science Education Resource Center at Carleton College say optimal growing temperatures for thermophiles range from 60 to 108 degrees Celsius.
Many organisms cannot survive in overly salty conditions, but halophiles thrive in salty environments, according to the American Society for Microbiology. Methanogens are often found in wetlands and within the human digestive system. These organisms produce methane as a byproduct of some chemical processes. In humans, the methane is released in the form of flatulence or belching, explains Wikipedia. In wetlands, methanogens produce the methane that gives marsh gas its characteristic odor.