Chelicerata Heymons, 1901 see Superclass Chelicerata Heymons, 1901
   Euchelicerata Weygoldt & Paulus, 1979
     1 [Class] Xiphosura Latreille, 1802 - horseshoe crabs
     2 [Order] †Chasmataspidida Caster & Brooks, 1956
     3 [Order] †Eurypterida Burmeister, 1843 - eurypterids
     4 [Class] Arachnida Lamarck, 1801