• Animal Systematics, Evolution and Diversity
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• v.17 no.2
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• pp.263-275
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• 2001

Animal phyla in the traditional animal phylogeny were organized into an order of increasing body plan complexity, which was based on the similarities in early embryonic stages. Molecular phylogeny mainly by 18S rRNA data provides recently re-evaluation of the traditional evolutionary scenario. The current molecular-based view of animal relationships strongly suggest the burst of two groups regraded as intermediate grades of body complexity in the traditional concept and displacement of them into higher positions in the tree. The new animal tree provides a framework within new picture of bilaterian ancestor could be drawn, and comparative developmental and genomic data to be interpreted.