Archaea are single celled microorganisms with no nucleus or organelles. They have four phyla. The most studied of the phyla are the Crenarchaeota and the Euryarchaeota. Crenarchaeota are the more strict anaerobes. They are found in Yellowstone Park and deep sea volcanos. They are thought to assemble the ancestor of archaea and are the most extreme thermophiles. Euryarchaeota produce methane and are found in intestines.   The majority of archaea has never been studied. Archaea reproduce asexually through binary fission.  They swim with their flagella. They are extremophiles and can survive in many environments such as the extreme cold, salt and radioactive environments. They make up 20% of the world’s biomass. Little is known about the deep-sea varieties. There has been research that shows Archaea resemble gram positive bacteria.  Archaea and bacteria are similar in shape and size. They both have no interior membranes of organelles. The cell membranes are bound by a cell wall. The phospholipids making up the cell membranes in archaea are made of glycerol-ether lipids while in bacteria and eukaryotes they are made up of glycol-ester lipids. Archaeal cell walls do not have peptidoglycan. Archaeal lipids lack the fatty acids found in Bacteria and Eukaryotes and instead have side chains composed of repeating units of isoprene. Like Bacteria, Archaea have 70S ribosomes, but they have a different shape. They both have flagella but bacteria flagellum is hallow and is assembled of subunits moving up while archaeal flagella has the addition of subunits at the base. The genes and metabolic pathways of archaea are closer to those of eukaryotes rather than bacteria. Archaea have more complex RNA polymerases than bacteria, similar to eukaryotes.