procaryotes
   Domain Bacteria Woese et al. 1990
     Phylum Aquificae Reysenbach 2001
       Class Aquificae Reysenbach 2001 nom. inval. see Class Aquificae Reysenbach 2002
         Order Aquificales Reysenbach 2001 nom. inval. see Order Aquificales Reysenbach 2002
           Family Aquificaceae Reysenbach 2001 nom. inval. see Family Aquificaceae Reysenbach 2002
             1 Genus Aquifex Huber and Stetter 1992
             2 Genus Calderobacterium Kryukov et al. 1984 see Genus Hydrogenobacter Kawasumi et al. 1984
             3 Genus Hydrogenobacter Kawasumi et al. 1984
             4 Genus Thermocrinis Huber et al. 1999