Archaeum

Archaea (Archaebacteria) Temporal range: Paleoarchean or perhaps Eoarchean – recent Had'n Archean Proterozoic Pha.
Halobacterium sp. strain NRC-1, each cell about 5 μm long
Scientific classification
Superdomain:	Neomura
Domain:	Archaea Woese, Kandler & Wheelis, 1990
Kingdoms and phyla
"Euryarchaeota" Woese et al. 1990 "DPANN" "Aenigmarchaeota" Rinke et al. 2013 "Diapherotrites" Rinke et al. 2013 "Nanoarchaeota" Huber et al. 2002 "Nanohaloarchaeota" Rinke et al. 2013 "Micrarchaeota" Baker et al. 2010 "Pacearchaeota" Castelle et al. 2015 "Parvarchaeota" Rinke et al. 2013 "Woesearchaeota" Castelle et al. 2015 "Proteoarchaeota" Petitjean et al. 2014 ("TACK") "Aigarchaeota" Nunoura et al. 2011 "Bathyarchaeota" Meng et al. 2014 Crenarchaeota Garrity & Holt 2002 "Geoarchaeota" Kozubal et al. 2013 "Korarchaeota" Barns et al. 1996 Thaumarchaeota Brochier-Armanet et al. 2008 "Asgard" Katarzyna Zaremba-Niedzwiedzka1 et al. 2017 "Lokiarchaeota" Spang et al. 2015 "Thorarchaeota" Seitz et al. 2016 "Odinarchaeota" Katarzyna Zaremba-Niedzwiedzka1 et al. 2017 "Heimdallarchaeota" Katarzyna Zaremba-Niedzwiedzka1 et al. 2017
Synonyms
Archaebacteria Woese & Fox, 1977 Mendosicutes Gibbons & Murray, 1978 Metabacteria Hori and Osawa 1979

The Archaea (ⁱ/ɑːrˈkiːə/ or /ɑːrˈkeɪə/ ar-KEE-ə or ar-KAY-ə) constitute a domain and kingdom of single-celled microorganisms. These microbes (archaea; singular archaeon) are prokaryotes, meaning that they have no cell nucleus or any other membrane-bound organelles in their cells.

Archaea were initially classified as bacteria, receiving the name archaebacteria (in the Archaebacteria kingdom), but this classification is outdated. Archaeal cells have unique properties separating them from the other two domains of life, Bacteria and Eukaryota. The Archaea are further divided into multiple recognized phyla. Classification is difficult because the majority have not been isolated in the laboratory and have only been detected by analysis of their nucleic acids in samples from their environment.