Chapter

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

Andreas Hejnol and Mark Q. Martindale

in Animal Evolution

Published in print August 2009 | ISBN: 9780199549429
Published online September 2009 | e-ISBN: 9780191721601 | DOI: http://dx.doi.org/10.1093/acprof:oso/9780199549429.003.0004
 The mouth, the anus, and the blastopore—open questions about questionable openings

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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

Chapter.  4799 words.  Illustrated.

Subjects: Evolutionary Biology

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