Fishes
   Class Elasmobranchii Bonaparte, 1838 see Subclass Elasmobranchii Bonaparte, 1838
     Order Hexanchiformes Compagno, 1973 - six-gill sharks
       1 Family Hexanchidae Gray, 1851 - cow sharks
       2 Family Chlamydoselachidae Garman, 1884 [monotypic] - frill sharks