Chelicerata Heymons, 1901
Count: 2c;12o; †6o;2f;23g
   †Eurypterida Burmeister, 1843 - eurypterids
  Count: [†g] †21f;73g [26 Dec 2020]
     †Eurypterina Burmeister, 1843
    Count: [†g] †13f;42g [26 Dec 2020]
       Superfamily †Megalograptoidea Caster & Kjellesvig-Waering, 1955 [monotypic]
      Count: [†g] †1f;2g [25 Dec 2020]
         Family †Megalograptidae Caster & Kjellesvig-Waering, 1955
        Count: [†g] †2g [25 Dec 2020]
           Genus †Echinognathus Walcott, 1882
          Count: -