Archaea
![](/Images/godic/202501/26/Halobacteria4643.jpg")
![Archaea were first found in extreme environments, such as volcanic hot springs. Pictured here is Grand Prismatic Spring of Yellowstone National Park.](/Images/godic/202501/26/Grand_prismatic_spring4643.jpg")
![The ARMAN are a new group of archaea recently discovered in acid mine drainage.](/Images/godic/202501/26/Rio_tinto_river_CarolStoker_NASA_Ames_Research_Center4643.jpg")
![Membrane structures. Top, an archaeal phospholipid: 1, isoprene chains; 2, ether linkages; 3, L-glycerol moiety; 4, phosphate group. Middle, a bacterial or eukaryotic phospholipid: 5, fatty acid chains; 6, ester linkages; 7, D-glycerol moiety; 8, phosphate group. Bottom: 9, lipid bilayer of bacteria and eukaryotes; 10, lipid monolayer of some archaea.](/Images/godic/202501/26/Archaea_membrane.svg4643.png")
The Archaea (/ɑːrˈkiːə/ or /ɑːrˈkeɪə/ ar-KEE-ə or ar-KAY-ə; singular archaeon) constitute a domain and kingdom of single-celled microorganisms. These microbes are prokaryotes, meaning that they have no cell nucleus or any other membrane-bound organelles in their cells.