†Placodermi McCoy, 1848 †Arthrodira Woodward, 1891 †Brachythoraci Gross, 1932 †Eubrachythoraci Miles, 1971 †Pachyosteomorphi Stensiö, 1944 †Aspinothoracidi Stensiö, 1959 Genus †Gymnotrachelus Dunkle & Bungart, 1939 [monotypic] †Gymnotrachelus hydei Dunkle & Bungart, 1939