Kingdom Monera contains two very distinct groups, the eubacteria and archaebacteria, but both usually have cell walls surrounding cell membranes, which contain loosely bound DNA and DNA rings but no membrane-bound organelles. Both types come in spherical, rod-shaped and elongated helix forms, while archaea also occasionally have triangular and other forms. These single-celled organisms are generally much smaller and simpler than cells that have nuclei and organelles.
Kingdom Monera is somewhat obsolete within modern biological science, as eubacteria and archaebacteria are actually considered to be nearly as different from each other as either is from eukaryotes. They were originally put together because both are small cells that lack a nucleus, but research shows that, in both chemistry and habits, they often vary greatly. Both their cell walls, when present, and their cell membranes have different chemistry from one another. Indeed, the cell membranes of archaebacteria are unique to them, while those of the eubacteria are essentially the same as those of eukaryotes.
Archaebacteria specialize in extreme environments, including high temperatures, acidic environments and highly saline environments. This is partially because of their unique cell membranes, which are more stable under extreme conditions than those of other organisms. However, according to Palomar College, the greatest reason for dividing the two groups of prokaryotes is their radically different DNA.