Archaebacteria are actually not animals. Animals are multicellular organisms comprised of eukaryotic cells (having a nucleus). Archaebacteria are single celled prokaryotes. They are not considered bacteria and are considered a separate domain in the three domain system (the other two are bacteria and eukarya).

Archaebacteria tend to live in extreme environments. One example is methanopyrus kandleri which can live at temperatures above 100 degrees celsius (above the boiling temperature of water) and was discovered living in sea vents on the ocean floor. Another example is methanobrevibacter smithii which is found in the human digestive system.