procaryotes
   Domain Archaea Woese et al. 1990
     Phylum Crenarchaeota Garrity and Holt 2001
       Class Thermoprotei Reysenbach 2001 see Class Thermoprotei Reysenbach 2002
         Order Desulfurococcales Huber and Stetter 2001 nom. inval. see Order Desulfurococcales Huber and Stetter 2002
           Family Pyrodictiaceae Burggraf et al. 1997
             Genus Pyrodictium Stetter et al. 1984