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अमूर्त

Larvae, Lophophores and Chimeras in Classification

Donald I Williamson

I challenge the widely held assumption, reflected in current classifications, that larvae and corresponding adults evolved from common ancestors and that animals with lophophores evolved from an ancestral lophophorate. Types of animal development are defined, and their origins are discussed in relation to the common ancestor hypothesis and hybridogenesis, the proposal that new life forms have been generated by hybridization. Echinoderms are commonly classified by their larval characteristics as bilateral enterocoelous deuterostomes. However, some echinoderms without larvae develop as radial schizocoelous protostomes, which would place them in a different superphylum from those with larvae. Current classifications also place some hemichordates in a different superphylum from other hemichordates. A genetic study concludes that lophophorates are not descended from a common ancestor, thus invalidating the clade Lophotrochozoa. I propose that lophophorates and barnacles are chimeras, with components from different phyla. The evidence consistently supports the view that both larvae and lophophores were later additions to life histories. F M Balfour (1851-1882) recognized that larvae were later additions to life histories, and there were no echinoderm larvae until after the establishment of the classes of that phylum. He has been ignored, and, as a result, animal taxonomy has been on the wrong road since the late 19th century.