Domain Archaea Woese et al. 1990 Phylum Crenarchaeota Garrity and Holt 2001 Class Thermoprotei Reysenbach 2001 see Class Thermoprotei Reysenbach 2002 Order Thermoproteales Zillig and Stetter 1982 1 Family Thermoproteaceae Zillig and Stetter 1982 2 Family Thermofilaceae Burggraf et al. 1997