Eubacteria are also called true bacteria. They are characterised by the presence of a rigid cell wall and if motile a flagellum. Eubacteria include various subgroups like Cyanobacteria, Mycoplasma, Actinomycetes, etc. Archaebacteria are different from other bacteria in having different cell wall structure. Archaebacteria is unique since they live in some of the harshest environments such as hot springs (thermoacdiophiles), extremely salty areas (halophiles), too marshy areas (methanogens). Methanogens can convert CO2, methanol, formic acid into methane so are called methanogens. They are found in the biogas plant and are a subgroup of archaebacteria. Example: Methanobacterium.