Vertebrata Cuvier, 1812 - vertebrates Gnathostomata Class Chondrichthyes Huxley, 1880 - cartilaginous fishes Subclass Elasmobranchii Bonaparte, 1838 - shark-like fishes Superorder Euselachii Hay, 1902 see Infraclass Euselachii Hay, 1902 Order †Xenacanthida Glikman, 1964 see Order Xenacanthiformes Berg, 1955 1 Family †Diplodoselachidae Dick, 1981 2 Family †Xenacanthidae Fritsch, 1889