prokaryotes - bacteria see Domain Bacteria Woese et al. 1990
   Domain "Bacteria" Woese et al. 1990
     Phylum "Aquificae" Reysenbach 2001 [monotypic]
       Class Aquificae Reysenbach 2002 [monotypic]
         Order Aquificales Reysenbach 2002
           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 Hydrogenivirga Nakagawa et al. 2004
             4 Genus Hydrogenobacter Kawasumi et al. 1984
             5 Genus Hydrogenobaculum Stöhr et al. 2001
             6 Genus Thermocrinis Huber et al. 1999