Procaryotic Genera
   Domain "Archaea" Woese et al. 1990
     Phylum Euryarchaeota Garrity and Holt 2001
       Class Methanococci Boone 2001 nom. inval. see Class Methanococci Boone 2002
         Order Methanomicrobiales Balch and Wolfe 1981
           1 Family Methanomicrobiaceae Balch and Wolfe 1981
           2 Family Methanocorpusculaceae Zellner et al. 1989 [monotypic]
           3 Family Methanospirillaceae [monotypic] see Family Methanospirillaceae Boone et al. 2002
           4 Genus Methanocalculus Ollivier et al. 1998, incertae sedis