Mitochondrial genome sequence and gene order of Sipunculus nudus give additional support for an inclusion of Sipuncula into Annelida.
BACKGROUND
Mitochondrial genomes are a valuable source of data for analysing phylogenetic relationships. Besides sequence information, mitochondrial gene order may add phylogenetically useful information, too. Sipuncula are unsegmented marine worms, traditionally placed in their own phylum. Recent molecular and morphological findings suggest a close affinity to the segmented Annelida.


RESULTS
The first complete mitochondrial genome of a member of Sipuncula, Sipunculus nudus, is presented. All 37 genes characteristic for metazoan mtDNA were detected and are encoded on the same strand. The mitochondrial gene order (protein-coding and ribosomal RNA genes) resembles that of annelids, but shows several derivations so far found only in Sipuncula. Sequence based phylogenetic analysis of mitochondrial protein-coding genes results in significant bootstrap support for Annelida sensu lato, combining Annelida together with Sipuncula, Echiura, Pogonophora and Myzostomida.


CONCLUSIONS
The mitochondrial sequence data support a close relationship of Annelida and Sipuncula. Also the most parsimonious explanation of changes in gene order favours a derivation from the annelid gene order. These results complement findings from recent phylogenetic analyses of nuclear encoded genes as well as a report of a segmental neural patterning in Sipuncula.
Mwinyi
Adina
A
Institut für Zoologie, Freie Universität Berlin, Berlin, Germany. adina.mwinyi@gmx.de
Meyer
Achim
A
Bleidorn
Christoph
C
Lieb
Bernhard
B
Bartolomaeus
Thomas
T
Podsiadlowski
Lars
L
D000818:Animals; D000845:Annelida / Q000145:classification* / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D023061:Gene Order; D050259:Genes, Mitochondrial; D054629:Genome, Mitochondrial; D009348:Nematoda / Q000145:classification* / Q000235:genetics; D010802:Phylogeny; D017422:Sequence Analysis, DNA
D004272:DNA, Mitochondrial