procaryotes
   Domain Archaea Woese et al. 1990
     Phylum Euryarchaeota Garrity and Holt 2001
       Class Thermoplasmata Reysenbach 2001 see Class Thermoplasmata Reysenbach 2002
         Order Thermoplasmatales Reysenbach 2001 see Order Thermoplasmatales Reysenbach 2002
           Family Picrophilaceae Schleper et al. 1996
             Genus Picrophilus Schleper et al. 1996