fossil marine animal genera Linnaeus, 1758 - animals
   Phylum Arthropoda Siebold, 1848 - arthropods
     Class Merostomata Dana, 1852 - horseshoe crabs see Class Xiphosura Latreille, 1802
       1 ?Order †Aglaspida (Walcott, 1911), nom. illeg. see Order Aglaspidida Walcott, 1911
       2 Order †Chasmataspidida Caster & Brooks, 1956
       3 Order Xiphosurida Latreille, 1802
       4 Order †incertae sedis
       5 Order †Eurypterida Burmeister, 1843 - eurypterids