Chelicerata Heymons, 1901 see Superclass Chelicerata Heymons, 1901
   Euchelicerata Weygoldt & Paulus, 1979
     [Class] Xiphosura Latreille, 1802 - horseshoe crabs
       1 †"synziphosurines"
       2 [Order] Xiphosurida Latreille, 1802