DOMAIN ARCHAEA: Kingdom Archaebacteria
Single-celled prokaryotic organisms that lack peptidoglycan cell walls and have distinctive ribosomal RNA sequences.
The Archaebacteria include methanogens (organisms that produce methane gas, such as Methanobacterium), salt-loving bacteria (Halococcus), and thermoacidophilic bacteria (Thermoplasma), which grow in extremely high temperatures.