Phylum Chordata Bateson, 1885 - chordates Subphylum Vertebrata Cuvier, 1812 - vertebrates Class Chondrichthyes Huxley, 1880 - cartilaginous fishes Order Hexanchiformes Compagno, 1973 - six-gill sharks 1 Family Hexanchidae Gray, 1851 - cow sharks 2 Family Chlamydoselachidae Garman, 1884 - frill sharks