Major rearrangements characterize the mitochondrial genome of the isopod Idotea baltica (Crustacea: Peracarida).

Mitochondrial genomes represent an important data source for phylogenetic analyses. Thirty-seven genes encoding for 13 protein subunits, 2 rRNAs and 22 tRNAs are usually present in a bilaterian mitochondrial genome (Boore, 1999; Wolstenholme, 1992). Additionally, a noncoding control region can be identiWed in most cases, probably bearing the transcription initiation sites. DiVerent rates of evolutionary change between diVerent parts of the mitochondrial genome make them useful for a variety of phylogenetic questions ranging from studies at the population level (mitochondrial control region, cytochrome c oxidase subunit I and cytochrome b, e.g., Liebers et al., 2004) up to the interrelationships of animal phyla (concatenated amino acid alignments of protein-coding genes, e.g., Helfenbein et al., 2004; Lavrov et al., 2005). Besides nucleotide or amino acid sequences other types of characters may be useful in phylogenetic studies, like for instance gene order (e.g., Boore et al., 1995; Roehrdanz et al., 2002), RNA secondary structure (e.g., Macey et al., 2000) or changes of mitochondrial genetic code (e.g., Castresana et al., 1998). Mitochondrial gene order is not stable among Crustacea. Major gene rearrangements involving several proteincoding genes have been reported in copepods (Machida et al., 2002, 2004; Tjensvoll et al., 2005), an ostracod (Ogoh and Ohmiya, 2004), a branchiuran (Lavrov et al., 2004), and among Malacostraca in the freshwater crayWsh Cherax destructor (Miller et al., 2004) and the crab Eriocheir sinenesis (Sun et al., 2005). Taxon sampling regarding complete mitochondrial genomes among Malacostraca remains rather poor. Besides several decapod and stomatopod spe-