Further phylogenetic studies of the Polychaeta using 18S rDNA sequence data

Abstract

The integration of molecular and morphological approaches has produced substantial progress in understanding the higher classification of most major invertebrate groups. The striking exception to this is the Polychaeta. Neither the membership nor the higher classification of this group has been robustly established. Major inconsistencies exist between the only comprehensive cladistic analysis of Polychaeta using morphological data and the DNA sequence studies covering all or part of the taxon.We have compiled a dataset of available nearly complete 18S ribosomal DNA sequences and collected an additional 22 sequences (20 Polychaeta in 19 taxa, one Myzostomida and one Phoronida) to obtain more comprehensive coverage of polychaete diversity for this gene. Analyses of the data do not resolve all inconsistencies among current hypotheses of polychaete phylogeny. They do support the recognition (in whole or part) of some clades such as the Eunicida, Phyllodocida and Terebellida that have been proposed on morphological grounds. Our analyses contradict the Canalipalpata and the Scolecida. Although the polychaete sister-group to the Clitellata is not clearly resolved in our analyses, the clitellates are always recovered as a derived clade within the Polychaeta. Increased taxon sampling is required to elucidate further the phylogeny of the Polychaeta.

MicroRNAs resolve an apparent conflict between annelid systematics and their fossil record

“…has been sequenced, and the morphological cladistic analysis of Rouse & Fauchald (1997) resolved the last common ancestor of Capitella and Nereis as the last common ancestor of all living polychaetes. Furthermore, although virtually all molecular analyses suggest that polychaetes are paraphyletic, all show that clitellates are more closely related either to Capitella or to Nereis among the polychaetes considered (Bleidorn et al 2003;Hall et al 2004;Colgan et al 2006;Rousset et al 2006;Struck et al 2007;Dunn et al 2008). Thus, for an initial investigation into miRNA evolution in annelids, analysing the descendants of the last common ancestor of Capitella and Nereis captures much of modern polychaete, if not modern annelid, diversity.…”

Hox gene expression in larval development of the polychaetes Nereis virens and Platynereis dumerilii (Annelida, Lophotrochozoa)

“…The larvae of these nereids form a peristomial segment and three parapodial segments, whereas the adult animals have dozens of morphologically similar segments. Morphological, developmental, and genome characteristics of nereids make us believe that these worms retain many primitive characteristics of the annelids (Arendt 2003;TessmarRaible and Arendt 2003;Raible et al 2005), the molecular phylogeny of which remains problematic (Bleidorn et al 2003;Hall et al 2004;Seaver et al 2005). Using RT-PCR and WMISH, we have examined patterns of Hox gene expression during development in these animals, from early trochophore to nectochaete larva.…”

Phylogeny of sipunculan worms: A combined analysis of four gene regions and morphology

“…Several recent publications focusing on systematics of annelids based on DNA sequence data included sipunculans and unanimously placed them in the annelid ingroup, although the number of outgroups was sometimes limited (Brown et al, 1999) and the branch support was generally low for deep nodes in the tree (Bleidorn et al, 2003a,b;Hall et al, 2004). Better resolution and support for deep relationships was achieved by Telford et al (2005) who presented a phylogeny of the Bilateria, based on 72 complete 18S ribosomal RNA sequences.…”