A Reexamination of the Arachnid Theory on the Origin of Vertebrata

A method of phylogenetic classification, based on Hennig's theory of cladism and Sokal and Sneath's theory of numerical taxonomy, is outlined. The necessity of using non‐morphological characters in superphyletic classification is argued. It is suggested that the vertebrates arose from members of the annelid superphylum, an alternative implied by the Arachnid theory advocated by Gaskell and Patten. A testing of this theory by reference to non‐morphological characters corroborates the affiliation between Vertebrata and the annelid superphyium, but the available data do not warrant a definite answer as concerns the theory.