The term archaebacteria refers to the ancient origin of this group of bacteria, which seems to have diverged very early from the eubacteria. All archaebacteria share certain key characteristics. (i) Their cell wall lack peptidoglycan (important component of cell wall of eubacteria). (ii) Lipids in cell membrane of archaebacteria have different structure than those in all other organisms. (iii) Archaebacteria have distinct ribosomal RNA sequence. (iv) Some genes of archaebacteria possess introns unlike those of other bacteria.