Which is the best characteristic that distinguishes the kingdom archaebacteria from the kingdom eubacteria

Archaebacteria are the oldest living organisms on earth. They are prokaryotes and unicellular. Archaebacteria are found in very harsh conditions (such as at the bottom of the sea or in volcanic vents). This is thought to be because the early Earth’s atmosphere was filled with poisonous gases and was very hot – nothing could survive, except the archaebacteria. These slowly gave way to modern organisms when the Earth’s conditions settled down and oxygen was introduced to the atmosphere. " 

the glands which are associated with each description is given below:

pancreas - is an endocrine and exocrine gland that secretes juices with enzymes for digestion. salivary glands- with protection and digestion in the mouth. liver- secretes bile for digestion.   lachrymal glands - secrete tears to moisten eyes and protect them from particles and infection.   sweat gland -regulates water, salt, and temperature. oil glands - to form a protective barrier on the skin.   goblet cells - secrete mucus for protection.