procaryotes Domain Archaea Woese et al. 1990 Phylum Euryarchaeota Garrity and Holt 2001 Class Methanococci Boone 2001 nom. inval. see Class Methanococci Boone 2002 Order Methanococcales Balch and Wolfe 1981 Family Methanococcaceae Balch and Wolfe 1981 Genus Methanococcus Kluyver and van Niel 1936 (Approved Lists 1980)