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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 Triploblastica is a clade consisting of species with three germ layers: the primary ectoderm and endoderm, and the secondary mesoderm. Mesoderm is often organised as epithelial cells that exhibit a pronounced polarity with a basal membrane at the basal surface, septate/tight cell junctions, and Golgi apparatus in the apical part and sometimes one or more cilia at the apical pole. The name Acrosomata was used for the triploblasts, but the homoscleromorphs are now known to have an acrosome. Mesoderm formed from various parts of the archenteron is present both in deuterostomes and the chaetognaths (now classified as protostomes). On the basis of morphology, ctenophores are classified as triploblasts.

Keywords:   triploblasts, Triploblastica, ectoderm, endoderm, mesoderm, epithelial cells, homoscleromorphs, deuterostomes, chaetognaths, ctenophores

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