Domain Bacteria Woese et al. 1990
   Phylum Proteobacteria Garrity and Holt 2001 see Phylum Proteobacteria Garrity et al. 2005
     Class "Gammaproteobacteria" nom. inval. see Class Gammaproteobacteria Garrity et al. 2005
       Order "Thiotrichales" see Order Thiotrichales Garrity et al. 2005
         Family "Piscirickettsiaceae" see Family Piscirickettsiaceae Fryer and Lannan 2005
           Genus Cycloclasticus Dyksterhouse et al. 1995
           Genus Hydrogenovibrio Nishihara et al. 1991
           Genus Methylophaga Janvier et al. 1985
           Genus Thiomicrospira Kuenen and Veldkamp 1972 (Approved Lists 1980)
           1 Genus Piscirickettsia Fryer et al. 1992