Vertebrata Cuvier, 1812 - vertebrates see Infraphylum Vertebrata Lamarck, 1801
   Class Agnatha Cope, 1889 [paraphyletic]
     Subclass Cephalaspidomorpha see Class Agnatha Cope, 1889
       Order †Osteostraci Lankester, 1868 - osteostracans see Order Cephalaspidiformes Halstead Tarlo, 1967
         1 Family †Tremataspidae Woodward, 1891 see Family Tremataspididae Woodward, 1891, nom. praeval.
         2 Family †Dartmuthiidae Robertson, 1935 see Family Tremataspididae Woodward, 1891, nom. praeval.
         3 Family †Ateleaspidae Traquair, 1899 see Family Ateleaspididae Traquair, 1899, nom. praeval.
         4 Family †Sclerodontidae Berg, 1940 see Family Tremataspididae Woodward, 1891, nom. praeval.
         5 Family †Cephalaspidae Agassiz, 1844 see Family Cephalaspididae Agassiz, 1844, nom. praeval.
         6 Family †Kiaeraspididae Stensiö, 1932, nom. praeval.