R A Jenner, University of Bath, Bath, UK © 2007 Elsevier Inc. All rights reserved.
1.02.1 Introduction to Metazoan Phylogeny 17
1.02.1.2 Methods 20
1.02.2 Overview of Major Metazoan Clades and Grades 21
1.02.2.1 Nonbilaterians and Acoelomorpha 21
1.02.2.2 Deuterostomia 23
1.02.2.3 Ecdysozoa 23
1.02.2.4 Lophotrochozoa 24
1.02.3 Phylogenetic Relationships Within the Major Clades and Grades 24
1.02.3.1 Nonbilaterians: Porifera, Placozoa, Ctenophora, Cnidaria, and Myxozoa 24
1.02.3.2 Acoelomorpha: Acoela and Nemertodermatida 27
1.02.3.3 Deuterostomia 27
1.02.3.4 Ecdysozoa 31
1.02.3.5 Lophotrochozoa 34
1.02.4 Conclusion and Future Progress 37
Glossary apomorphy body plan clade coelom crown group eumetazoa grade homoplasy
An evolutionarily derived character or character state, an evolutionary novelty. An autapomorphy refers to a derived character or character state unique for a single taxon; a synapomor-phy refers to a shared derived character or character state possessed by at least two taxa.
Set of characters primitively shared by the members of a clade, irrespective of taxonomic level. These characters both include ancestrally inherited plesiomor-phies and newly evolved apomorphies for that clade.
Monophyletic taxon, all descendants from a most recent common ancestor. Internal body cavity lined by a mesoder-mally derived epithelium. A clade of extant taxa, as distinct from a stem group (see also 'stem group'). Metazoa minus Porifera (traditionally Eumetazoa also excluded Placozoa, but new molecular findings indicate a less basal position of Placozoa). A paraphyletic group of taxa. Independently evolved, nonhomolo-gous features, such as convergences and independent losses. Important developmental regulatory genes involved in specifying positional information along animal body axes, including appendages. Having a single evolutionary origin. A monophyletic taxon includes an paraphyletic phylum plesiomorphy sister taxon stem group synapomorphy ancestor and all its descendants. See also 'paraphyletic'.
Having a single evolutionary origin, but differing from a monophyletic taxon by including an ancestor, but only a subset of its descendants.
Highest Linnean category for classification of animals.
Ancestral character or character state. The closest relative of a given taxon. A clade or grade of extinct taxa, as distinct from a crown group. See 'apomorphy'.
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