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 Methanomicrobiales Balch and Wolfe 1981
           1 Family Methanomicrobiaceae Balch and Wolfe 1981
           2 Family Methanocorpusculaceae Zellner et al. 1989
           3 Family Methanospirillaceae see Family Methanospirillaceae Boone et al. 2002
           4 ?Genus Methanocalculus Ollivier et al. 1998