Genetic Identification of the Northeastern Atlantic Spiny Spider Crab as Maja Brachydactyla Balss, 1922

Abstract The northeastern Atlantic spiny spider crab occurs from the British Islands to Senegal, where it is an important fishery resource. From morphological characters this crab has recently been proposed as a distinct species, Maja brachydactyla, although for commercial purposes it is still considered the same species as its Mediterranean congener M. squinado. We have studied variation at two mitochondrial genes in several crab populations from the Atlantic (putatively M. brachydactyla) and Mediterranean (M. squinado and M. crispata) basins, in order to clarify the taxonomic status of this crab in the northeastern Atlantic and Mediterranean regions. Phylogenetic analysis revealed that each of these three taxa forms a distinct and well-defined clade. While the divergence within each taxon was 0% for 16S and 0-0.3% for COI, divergence between taxa was 0.6-2.5% for 16S and 5.3-8.7% for COI; values that are in the range of the differences observed between other crustacean species. These results confirm the genetic distinctiveness of each taxa and support their designation as different species. Therefore, the Atlantic spider crab should be referred as M. brachydactyla, a fact that should be taken into account for conservation and commercial purposes.