MBE Advance Access originally published online on August 11, 2004
Molecular Biology and Evolution 2004 21(11):2122-2129; doi:10.1093/molbev/msh229
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Research Article |
Identification of Chaetognaths as Protostomes Is Supported by the Analysis of Their Mitochondrial Genome


* Centre d'Océanologie de Marseille, Marseille, France;
Laboratoire de Biologie Animale (Plancton), Université Aix-Marseille I, Marseille, France; and
Institut de Biologie du Développement de Marseille, Laboratoire de Génétique et Physiologie du Développement, Campus de Luminy, Marseille, France
E-mail: papillon{at}com.univ-mrs.fr.
Determining the phylogenetic position of enigmatic phyla such as Chaetognatha is a longstanding challenge for biologists. Chaetognaths (or arrow worms) are small, bilaterally symmetrical metazoans. In the past decades, their relationships within the metazoans have been strongly debated because of embryological and morphological features shared with the two main branches of Bilateria: the deuterostomes and protostomes. Despite recent attempts based on molecular data, the Chaetognatha affinities have not yet been convincingly defined. To answer this fundamental question, we determined the complete mitochondrial DNA genome of Spadella cephaloptera. We report three unique features: it is the smallest metazoan mitochondrial genome known and lacks both atp8 and atp6 and all tRNA genes. Furthermore phylogenetic reconstructions show that Chaetognatha belongs to protostomes. This implies that some embryological characters observed in chaetognaths, such as a gut with a mouth not arising from blastopore (deuterostomy) and a mesoderm derived from archenteron (enterocoely), could be ancestral features (plesiomorphies) of bilaterians.
Key Words: Chaetognatha mitochondria gene loss evolution phylogeny Spadella cephaloptera
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