Domain Archaea Woese et al. 1990 Phylum Euryarchaeota Garrity and Holt 2001 Class Methanobacteria Boone 2001 nom. inval. see Class Methanobacteria Boone 2002 Order Methanobacteriales Balch and Wolfe 1981 Family Methanothermaceae Stetter 1982 1 Genus Methanothermus Stetter 1982