procaryotes
   Domain Archaea Woese et al. 1990
     Phylum Euryarchaeota Garrity and Holt 2001
       Class Methanococci Boone 2001 nom. inval. see Class Methanococci Boone 2002
         1 Order Methanococcales Balch and Wolfe 1981
         2 Order Methanomicrobiales Balch and Wolfe 1981
         3 Order Methanosarcinales Boone et al. 2001 nom. inval. see Order Methanosarcinales Boone et al. 2002