†Placodermi McCoy, 1848
Count: [†*] †18f;24g;25s
   †Arthrodira Woodward, 1891
  Count: [†*] †18f;24g;25s
     †Brachythoraci Gross, 1932
    Count: [†*] †18f;23g;24s
       †Eubrachythoraci Miles, 1971
      Count: [†*] †18f;20g;22s [11 May 2017]
         †Pachyosteomorphi Stensiö, 1944
        Count: [†*] †14f;17g;18s [11 May 2017]
           †Aspinothoracidi Stensiö, 1959
          Count: [†*] †9f;8g;6s [12 May 2017]
             Genus †Gymnotrachelus Dunkle & Bungart, 1939 [monotypic]
            Count: [†*] †1s [10 May 2017]
               1 †Gymnotrachelus hydei Dunkle & Bungart, 1939
              Count: -