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Animal EvolutionGenomes, Fossils, and Trees$
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Maximilian J. Telford and D.T.J. Littlewood

Print publication date: 2009

Print ISBN-13: 9780199549429

Published to Oxford Scholarship Online: September 2009

DOI: 10.1093/acprof:oso/9780199549429.001.0001

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The mouth, the anus, and the blastopore—open questions about questionable openings

The mouth, the anus, and the blastopore—open questions about questionable openings

Chapter:
(p.33) CHAPTER 4 The mouth, the anus, and the blastopore—open questions about questionable openings
Source:
Animal Evolution
Author(s):

Andreas Hejnol

Mark Q. Martindale

Publisher:
Oxford University Press
DOI:10.1093/acprof:oso/9780199549429.003.0004

Gastrulation is one of the major events during the embryogenesis of an animal. In addition to the formation of the germ layers it is often the time when the future axial properties and digestive openings become apparent and it is not surprising that this event plays an important role in hypotheses regarding metazoan evolution. A major difference between these theories concerns the structure of the alimentary canal and the relationship of its openings to the blastopore of the last common bilaterian ancestor. Here we review competing theories of bilaterian evolution and evaluate their plausibility in the light of recent insights into metazoan phylogeny and development.

Keywords:   gastrulation, Gastraea-Theory, Acoeloid-Planuloid-Theory, amphistomy, protostomy

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