[Phylum] Chordata Bateson, 1885 - chordates
   Subphylum Craniata auct.
     Infraphylum Vertebrata Lamarck, 1801 - vertebrates
       Superclass Gnathostomata Gegenbaur, 1874 - jawed vertebrates
         Class Chondrichthyes Huxley, 1880 - cartilaginous fishes
           Subclass Euselachii Hay, 1902 - sharks, rays, and related fossils
             Infraclass Elasmobranchii Bonaparte, 1838
               Superorder Squalomorphi
                 Order Hexanchiformes Compagno, 1973 - six-gill sharks
                   1 Family Chlamydoselachidae Garman, 1884 - frill sharks
                   2 Family †Crassodontidanidae Kriwet & Klug, 2016
                   3 Family Hexanchidae Gray, 1851 - cow sharks
                   4 Family Heptranchidae Barnard, 1925