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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 Protostomia is a large clade of bilateral animals that are divided into Spiralia (Lophotrochozoa) and Ecdysozoa, based on molecular phylogenies. Previously known as Zygoneura, the group was named Protostomia based on the fate of the blastopore, which should develop into the mouth (rather than the anus, as in the Deuterostomia). Almost every morphological and molecular study points to the protostomes as monophyletic. The Chaetognatha is placed in a trichotomy with Spiralia and Ecdysozoa, with the morphology and ontogeny of its nervous system supporting their protostomian affinities. The origin and evolution of the characteristic trochophora larva and nervous system, along with the complex of the tubular gut, are explained by the trochaea theory.

Keywords:   bilateral animals, Protostomia, Spiralia, Ecdysozoa, blastopore, protostomes, Chaetognatha, nervous system, evolution, trochaea theory

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