31 Oct 2004 12:33 AR AR229-ES35-09.tex AR229-ES35-09.sgm LaTeX2e(2002/01/18) P1: GJB 10.1146/annurev.ecolsys.35.112202.130124 Annu. Rev. Ecol. Evol. Syst. 2004. 35:229–56 doi: 10.1146/annurev.ecolsys.35.112202.130124 Copyright c 2004 by Annual Reviews. All rights reserved First published online as a Review in Advance on September 2, 2004 THE NEW VIEW OF ANIMAL PHYLOGENY Kenneth M. Halanych Department of Biological Sciences, Auburn University, Auburn, Alabama 36849; email:
[email protected] KeyWords Metazoa, Lophotrochozoa, Ecdysozoa, Deuterostomia, Cambrian explosion ■ Abstract Molecular tools have profoundly rearranged our understanding of meta- zoan phylogeny. Initially based on the nuclear small ribosomal subunit (SSU or 18S) gene, recent hypotheses have been corroborated by several sources of data (including the nuclear large ribosomal subunit, Hox genes, mitochondrial gene order, concate- nated mitochondrial genes, and the myosin II heavy chain gene). Herein, the evidence supporting our current understanding is discussed on a clade by clade basis. Bilate- rian animals consist of three clades: Deuterostomia, Lophotrochozoa, and Ecdyso- zoa. Each clade is supported by molecular and morphological data. Deuterostomia is smaller than traditionally recognized, consisting of hemichordates, echinoderms, chor- dates, and Xenoturbella (an enigmatic worm-like animal). Lophotrochozoa groups ani- mals with a lophophore feeding apparatus (Brachiopoda, Bryozoa, and Phoronida) and trochophore larvae (e.g., annelids and mollusk), as well as several other recognized phyla (e.g., platyhelminthes, sipunculans, nemerteans). Ecdysozoa comprises molting animals (e.g., arthropods, nematodes, tardigrades, priapulids), grouping together two major model organisms (Drosophila and Caenorhabditis)inthe same lineage.