Natura - nature
   actualia - actual entities
     Mundus Plinius - physical world
       naturalia - natural bodies
         Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
           Domain Bacteria Woese et al. 2024
             Kingdom Pseudomonadati (Gibbons and Murray 1978) Oren and Göker 2024
               Phylum Pseudomonadotaᵀ Garrity et al. 2021
                 Class Betaproteobacteria Garrity et al. 2006
                   Order Spirillales Prévot 1940 (Approved Lists 1980)
                     1 Family Gallionellaceae Henrici and Johnson 1935 (Approved Lists 1980)
                     2 Family Methylophilaceae Garrity et al. 2006
                     3 Family Nitrosomonadaceae Garrity et al. 2006
                     4 Family Spirillaceaeᵀ Migula 1894 (Approved Lists 1980)
                     5 Family Sterolibacteriaceae Boden et al. 2017
                     6 Family Sulfuricellaceae Watanabe et al. 2015
                     7 Family Thiobacillaceae Boden et al. 2017
                     8 Family Usitatibacteraceae Vieira et al. 2021 [monotypic]