# Evolutionary they are primitive. They were the first to be born on our planet and they are present nowdays within their primitive characters. They are the "Oldest living fossils".
# Mostly archaebacteria are obligate anaerobes.
# Thermococcus, Methanococcus and Methanobacterium exemplify archaebateria that contain protien homologous to eukaryotic core histones.
# Their cell wall is not made up of peptidoglycan like that of eubacteria. Their cell wall is made up of complex polysaccharides and complex polypeptide.
#Their cell membrane is not a unit membrane, while in eubacleria the cell mernbrane is unit membrane .
Cell membrane of archaebacteria is highly complex because of branched lipid chain.
# In archaebacteria sequence of nucleotide in 16s- rRNA is differ from other prokaryote.

Archaebacteria includes following bacteria :

1. Methanogenes : "Methane producing bacteria"
(a) These bacteria convert carbon-di-oxides of swampy areas (Marshy) into methane. eg- Methanobacterium, Methanococcus, Methanomicrobium.
(b) These bacteria convert the organic substances (cellulose) present in cow dung into methane by fermentation (gobar gas fermenter). eg- Methanobacterium, Methanococcus, Methanomicrobium.
(c) An archaebacterium is found in the rumen of cattle as a symbiont, where it digest the cellulose and by fermentation convert it into merthane. eg- Rumenococcus

2. Halophiles : These archaebacteria are found in extreme salty areas.
Halophiles are surrounded by purple membrane in which a pigment 'bacteriorhodopsin' is found due to this reason membrane absorbs the bright light and directly forms ATP i.e. they can't prepare food (carbohydrates) like eubacteria. Instead of it they directly form ATP.

3. Thermo-acidophiles :
(a) These archaebacteria are found al those places where temperature is approx 80"C and medium is acidic [pH = 2]
(b) They are found in hot sulphur springs. These can also survive at 1OO"C temprature.
(c) Hot water sulphur springs are found in the Himalayan region.

Note : Barophyllic prokaryotes- Prokaryotes which grow and multiply in very deep marine sediments.