procaryotes
   Domain Archaea Woese et al. 1990
     Phylum Euryarchaeota Garrity and Holt 2001
       Class Methanopyri Garrity and Holt 2001 nom. inval. see Class Methanopyri Garrity and Holt 2002
         1 Order Methanopyrales Huber and Stetter 2001 nom. inval. see Order Methanopyrales Huber and Stetter 2002