The repeated appearance of strikingly similar crab–like forms in independent decapod crustacean lineages represents a remarkable case of parallel evolution. Uncertainty surrounding the phylogenetic relationships among crab–like lineages has hampered evolutionary studies. As is often the case, aligned DNA sequences by themselves were unable to fully resolve these relationships. Four nested mitochondrial gene rearrangements–including one of the few reported movements of an arthropod protein–coding gene–are congruent with the DNA phylogeny and help to resolve a crucial node. A phylogenetic analysis of DNA sequences, and gene rearrangements, supported five independent origins of the crab–like form, and suggests that the evolution of the crab–like form may be irreversible. This result supports the utility of mitochondrial gene rearrangements in phylogenetic reconstruction.