Chelicerata Heymons, 1901
   †Eurypterida Burmeister, 1843 - eurypterids
     †Eurypterina Burmeister, 1843
       †Diploperculata Lamsdell, Hoşgör & Selden, 2013
         Superfamily †Pterygotioidea Dunlop, Penney & Jekel, 2010, orth. inval. see Superfamily Pterygotoidea Clarke & Ruedemann, 1912
           Family †Hughmilleriidae Kjellesvig-Waering, 1951
             1 Genus †Herefordopterus Tetlie, 2006
             2 Genus †Hughmilleria Sarle, 1903