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Perspectives in Animal Phylogeny and Evolution$
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Alessandro Minelli

Print publication date: 2008

Print ISBN-13: 9780198566205

Published to Oxford Scholarship Online: May 2009

DOI: 10.1093/acprof:oso/9780198566205.001.0001

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Deep branches of the metazoan tree

Deep branches of the metazoan tree

(p.30) Chapter 4 Deep branches of the metazoan tree
Perspectives in Animal Phylogeny and Evolution

Alessandro Minelli

Oxford University Press

The phylogenetic value of characters such as the symmetry and polarity of the main body axis and the identity and number of germ layers recognizable during embryonic development and finally contributing to the animal's body structure is much less straightforward than traditionally assumed. Molecular phylogenetics and ultrastructural research have jointly demonstrated the paraphyletic nature of the sponges. It is still uncertain whether the remaining metazoans (Epitheliozoa) are more closely related to the Calcarea or to the Homoscleromorpha, although evidence for the former hypothesis has more frequently emerged from molecular analyses. Within the Epitheliozoa, the Placozoa are arguably the sister group of all other animals, the Eumetazoa. Within the latter, a basal position of both the Ctenophora and the Cnidaria is generally confirmed by modern phylogenetic analyses, but the mutual relationships of the Ctenophora, Cnidaria, and Bilateria are still under dispute.

Keywords:   Calcarea, Cnidaria, Ctenophora, Epitheliozoa, Eumetazoa, Hexactinellida, Homoscleromorpha, Placozoa, Radiata, sponges

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