[Kingdom] Animalia Linnaeus, 1758 - animals
   Grade Enterozoa
     Grade Cœlomata
       Phylum Appendiculata {Lankester}
         Branch Gnathopoda Straus-Durkheim, 1829
           Grade Condylopoda
             Class Arachnida Lamarck, 1801
               Branch Branchiopulmonata
                 Order Eurypterina Burmeister, 1843
                   1 Genus Pterygotus Agassiz, 1845
                   2 Genus Slimonia Page, 1856