prokaryotes - bacteria see Domain Bacteria Woese et al. 1990
   Domain "Archaea" Woese et al. 1990
     Phylum "Euryarchaeota" Garrity and Holt 2001
       Class "Methanomicrobia"
         1 Order Methanocellales Sakai et al. 2008 [monotypic]
         2 Order Methanomicrobiales Balch and Wolfe 1981
         3 Order Methanosarcinales Boone et al. 2002
         4 Genus Methanomassiliicoccus Dridi et al. 2012, incertae sedis