Cell wall contain glycoprotein or protein instead of polysaccharide
Some methanigens,salt-loving archaea and extreme thermophiles (sulfolobus thermoproteus abs pyrodictium) have glycoprotein in their walls.
In contrast other methanogens (methabococcus ethanomicrobium and methanogenium) and the extremec thermophile Desulfurococcus have protein walls.