living organisms see Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
   Eukaryotae see Domain Eukaryota Chatton, 1925
     Animalia Linnaeus, 1758 - animals
       Eumetazoa Butschli, 1910 see [unranked] Eumetazoa Bütschli, 1910
         Arthropoda Siebold, 1848 - arthropods
           Chelicerata Heymons, 1901
             Merostomata Dana, 1852 - horseshoe crabs see Class Xiphosura Latreille, 1802
               Xiphosura Latreille, 1802 see Class Xiphosura Latreille, 1802
                 1 †Aglaspida (Walcott, 1911), nom. illeg. see Order Aglaspida (Walcott, 1911), nom. illeg.
                 2 Xiphosurida R. & E. Richter, 1924 see Order Xiphosurida Latreille, 1802