[Phylum] Chordata Bateson, 1885 - chordates
   Subphylum Craniata auct.
     Infraphylum Vertebrata Lamarck, 1801 - vertebrates
       Class Petromyzontida [monotypic] - lampreys see Class Petromyzonti
         Order Petromyzontiformes Berg, 1940 - lampreys
           1 Family †Mayomyzontidae Bardack & Zangerl, 1971
           2 Family Petromyzontidae Bonaparte, 1831 - lampreys
           3 Family Geotriidae Gill, 1893 - pouched lampreys
           4 Family Mordaciidae Gill, 1893 - southern topeyed lampreys