[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
                 1 Order Xiphosura Latreille, 1802 see Class Xiphosura Latreille, 1802
                 2 Order Eurypterina Burmeister, 1843
                 3 Order Trilobitina