The Archaebacteria are a super-classification of odd bacteria that are neither prokaryotes nor eukaryotes; some scientists believe they represent a separate kingdom. The primary genus is Archaebacteria, whose members fall in three categories: microbes that can live in extremely salty environments (halophiles), microbes that produce methane (methanogens), and microbes that can live in extremely hot environments (thermophiles). All are of interest to biotechnologists because they have unique biochemical features (e.g., the enzymes of the theromophiles are extremely stable at high temperatures).

From the science dictionary at