I. Archaea Domain: They are prokaryotic, which have no nuclear membrane with distinct biochemistry and RNA markers from eubacteria, possess unique ancient evolutionary history due to which they are considered some of the oldest species of organisms on Earth; traditionally classified as archaebacteria; often characterized by living in extreme environments
Kingdom Archaebacteria: The Archaea are a group of single-celled microorganisms. A single individual or species from this domain is called an archaeon. They have neither have cell nucleus nor any other membrane-bound organelles (a specialized subunit within a cell that has a specific function) within their cells. In cell biology, the nucleus is a membrane-enclosed organelle found in eukaryotic cells. In the past they had been classed with bacteria as prokaryotes (or Kingdom Monera) and named archaebacteria, but this classification is regarded as outdated. Some examples are:
A. Methanogens: Methanogens are microorganisms which metabolize hydrogen and carbon dioxide into methane. They are common in wetlands.
B. Halophiles: Halophiles are extremophile organisms that thrive in environments with very high concentrations of salt. Extremophile organisms are the one that thrives in and may even require physically or geochemically extreme conditions.
C. Thermoacidophiles: These thrive in acid, sulfur rich and high temperatures (up to 110 °C).