[Phylum] Chordata Bateson, 1885 - chordates
   Subphylum Craniata auct.
     Infraphylum Vertebrata Lamarck, 1801 - vertebrates
       Superclass Gnathostomata Gegenbaur, 1874 - jawed vertebrates
         Class †Placodermi McCoy, 1848
           †Arthrodira Woodward, 1891
             Order †Phlyctaeniiformes
               Suborder †Brachythoraci Gross, 1932
                 †Pachyosteomorphi Stensiö, 1944 - pachyosteomorphs
                   Family †Rhachiosteidae Stensiö, 1963
                     Genus †Rhachiosteus Gross, 1938