prokaryotes - bacteria see Domain Bacteria Woese et al. 1990
   Domain "Archaea" Woese et al. 1990
     Phylum "Euryarchaeota" Garrity and Holt 2001
       Class "Methanomicrobia"
         Order Methanocellales Sakai et al. 2008 [monotypic]
           1 Family Methanocellaceae Sakai et al. 2008 [monotypic]