The mitochondrial genome of the Japanese skeleton shrimp Caprella mutica (Amphipoda: Caprellidea) reveals a unique gene order and shared apomorphic translocations with Gammaridea.

This study presents the complete mitochondrial (mt) genome of the amphipod Caprella mutica, an east-Asian species, which recently invaded the coastal regions of North America, Europe, and New Zealand. It is the first complete sequence of a member of the amphipod subclade Caprellidea. The mt genome has a total length of 15,427 bp and is organized in a circular double-strand molecule. All 37 mt genes are present, including the common set of 22 tRNAs. Particularly noticeable is the duplication of the control region (CR). The additional CR is located between nad6 and cob, and is almost identical to the original one. The most extensive changes in the gene order affect nad5 and a block consisting of trnH, nad4, nad4L, and trnP-all inserted near the original CR. The gene nad5 is also inverted. Furthermore, a comparison with the pancrustacean ground pattern reveals additional changes of individual tRNA genes. Some of these changes are also shared by Metacrangonyx longipes and Parhyale hawaiensis. These arrangements were found only in amphipods and might be considered as apomorphic by character states of Amphipoda. In all the three species, there is good evidence that trnG originated from a rare duplication/remolding event of the adjacent trnW gene. Nevertheless, each of the three available amphipod mitogenome sequences also bears unique rearrangements. C. mutica, however, shows the most extensive rearrangement in comparison with the pancrustacean ground pattern.