prokaryotes - bacteria see Domain Bacteria Woese et al. 1990
   Domain "Archaea" Woese et al. 1990
     Phylum "Euryarchaeota" Garrity and Holt 2001
       Class "Methanomicrobia"
         Order Methanomicrobiales Balch and Wolfe 1981
           Family Methanomicrobiaceae Balch and Wolfe 1981
             1 Genus Methanoculleus Maestrojuán et al. 1990
             2 Genus Methanofollis Zellner et al. 1999
             3 Genus Methanogenium Romesser et al. 1981
             4 Genus Methanolacinia Zellner et al. 1990
             5 Genus Methanomicrobium Balch and Wolfe 1981
             6 Genus Methanoplanus Wildgruber et al. 1984