Chelicerata
Heymons 1901 
Pycnogonida Latreille 1810 
Pycnogonum
= [Arachnopoda Dana 1853] 
Euchelicerata Weygoldt & Paulus 1979
Offacolus Orr et al. 2000
Prosomapoda nom. nov. 
(prosomal appendages II-V lacking exopods in the
adult instar)
?Andarella Moore, McKenzie & Lieberman 2007
?Borchgrevinkium Novojilov 1959
Camanchia Moore, Briggs, Braddy & Shulta 2011
Legrandella Eldredge 1974
Venustulus Moore in Moore et al. 2005
Weinbergina Richter & Richter 1929
Xiphosura Latreille 1802
= [Merostomata Dana 1952]
Kasibelinurus Pickett 1993
?Maldybulakia Tesakov &Alekseev 1998 = [Lophodesmus Tesakov & Alekseev 1992]
Willwerathia Stormer 1969
Xiphosurida Latreille 1802
(tergites of somites VIII-XIV dorsally fused into a thoracetron)
Planaterga nom. nov.
(lacking enlarged axial nodes on opisthosomal
tergites)
Bembicosoma Laurie 1899
?Bunaia Clarke 1919
Bundes d'Eichwald 1854 [= Exapinurus Nieszkowski 1859]
Cyamocephalus Currie 1927
Limuloides Woodward 1865 [= Hemiaspis Woodward 1864]
Pasternakevia Selden & Drygant 1987
Pseudoniscus Nieszkowski 1859 [= Neolimulus Woodward 1868]
Dekatriata nom. nov.
(19 somites; opistosoma plesiomorphically
consisting of 13 segments)
Chasmataspidida Caster & Brooks 1956 Chasmataspis
[= Diploaspida Simonetta & Delle Cave 1978 Diploaspis]
Sclerophorata Kamenz, Staude & Dunlop 2011
Eurypterida Burmeister 1843
[= Gigantostraca Haeckel 1866 ;
= Cyrtoctenida Stormer & Waterston 1968 Cyrtoctenus]
Arachnida Lamarck 1801