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Animal EvolutionInterrelationships of the Living Phyla$
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Claus Nielsen

Print publication date: 2011

Print ISBN-13: 9780199606023

Published to Oxford Scholarship Online: December 2013

DOI: 10.1093/acprof:oso/9780199606023.001.0001

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Animal Evolution

Claus Nielsen

Oxford University Press

The Eubilateria is a clade with a whole suite of morphological apomorphies and a monophyly supported by practically all molecular phylogenies and studies of Hox genes. One of the most well-defined metazoan groups, the Eubilateria, possesses a tubular gut with mouth and anus, together with a well-defined anterior brain and a long Hox cluster collinear with an anteroposterior axis. Bilateral symmetry is present in anthozoans, acoelomorphs, and a few hydrozoan polyps. Fossils resembling compact embryos with large cells, indicating lecithotrophy, date back to the Neoproterozoic, but the fossil record of adult organisms provides very little information about early animal radiation. The Eubilateria is traditionally divided into Protostomia and Deuterostomia, based on a number of morphological traits. This chapter describes several characters and organ systems of phylogenetic interest in order to shed light on the evolution and phylogenetic importance of the eubilaterians.

Keywords:   evolution, Eubilateria, eubilaterians, Hox genes, bilateral symmetry, anthozoans, acoelomorphs, radiation, Protostomia, Deuterostomia

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