| The phylum Arthropoda is the most speciose and, arguably, the most morphologically diverse within the Metazoa. While it is also one of the best studied, its phylogenetic position, monophyly and the relationships among and within its major lineages are still largely unresolved. The initial rapid radiation of arthropods during the “Cambrian explosion,” followed by more than 500 million years of evolution, often in similar environments, makes it very difficult, if not impossible, to untangle the arthropod relationships based on traditional morphological characters, or on DNA sequence comparisons.; We have approached this problem by determining complete mitochondrial DNA sequences from 12 representatives of major lineages of arthropods and potentially related groups of animals, and by combining a complex molecular character, the relative arrangement of genes on mitochondrial DNA (mtDNA) with DNA and amino acid sequence comparisons in our analysis.; We were able to clarify the arthropod relationships by showing that: (i) insects and crustaceans are united to the exclusion of chelicerates, onychophorans and myriapods; (ii) pentastomids, an enigmatic group of animals, are modified crustaceans likely to be related to cephalocarids; (iii) the Ecdysozoa hypothesis is supported by remarkable similarity of mitochondrial gene arrangements in Arthropoda, Tardigrada, Priapulida and, to a lesser extent, Nematoda; (iv) Nematoda may be included in Arthropoda and related to Pentastomida.; During the course of this study we have also discovered a new type of RNA editing in mitochondrial tRNAs of the centipede Lithobius forficatus . Finally, by determining complete mtDNA sequences from a diverse group of animals, we have created an important database for future genetic, phylogenetic, population, and other comparative studies. |
