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 Methanoregulaceae Sakai et al. 2012
             1 Genus Methanolinea Imachi et al. 2008
             2 Genus Methanoregula Bräuer et al. 2011
             3 Genus Methanosphaerula Cadillo-Quiroz et al. 2009