life see Clade Biota Wagner 2004 [Wiemann, de Queiroz, Rowe, Planavsky, Anderson, Gogarten, Turner & Gauthier 2020]
   Arthropoda Siebold, 1848 - arthropods
     1 [Class] Pycnogonida Latreille, 1810 - pycnogonids
     2.1 [Class] Xiphosura Latreille, 1802 - horseshoe crabs
     2.2 Class Arachnida Lamarck, 1801