Dekatriata is a clade of planatergan chelicerates including the groups Arachnida, Chasmataspidida, Eurypterida and additionally two stem-genera Winneshiekia and Houia. Dekatriata is defined by an opis

Planaterga is a clade of prosomapod euchelicerates including several synziphosurid genera and the group Dekatriata. Planaterga is defined by the opisthosoma with tergites broadest at third or fourth a