[Kingdom] Animalia Linnaeus, 1758 - animals
   Grade Enterozoa
     Grade Cœlomata
       Phylum Vertebrata (Lamarck, 1801)
         Branch Craniata Linnaeus, 1758
           Grade Cyclostoma
             Class Hyperoartia (Müller, 1844)
               Genus Petromyzon Linnaeus, 1758