Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         [crown] Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
           Domain Bacteria Woese et al. 1990 [paraphyletic?]
             Phylum Aquificae Reysenbach 2001 [monotypic]
               Class Aquificaeᵀ Reysenbach 2002
                 Order Aquificalesᵀ Reysenbach 2002
                   Family Aquificaceaeᵀ Reysenbach 2002
                     1 Genus Aquifexᵀ Huber and Stetter 1992 [monotypic]
                     2 Genus Hydrogenivirga Nakagawa et al. 2004
                     3.1 Genus Hydrogenobaculum Stöhr et al. 2001 [monotypic]
                     3.2 Genus Hydrogenobacter Kawasumi et al. 1984
                     4 Genus Thermocrinis Huber et al. 1999