Procaryotic Genera
   Domain "Archaea" Woese et al. 1990
     Phylum Euryarchaeota Garrity and Holt 2001
       Class Thermococci Zillig and Reysenbach 2001 [monotypic] see Class Thermococci Zillig and Reysenbach 2002
         Order Thermococcalesᵀ Zillig 1988 [monotypic]
           Family Thermococcaceae Zillig 1988
             1 Genus Thermococcusᵀ Zillig 1983
             2 Genus Palaeococcus Takai et al. 2000
             3 Genus Pyrococcus Fiala and Stetter 1986