Are Pecten maximus and Pecten jacobaeus different species?

Two members of the scallop genus Pecten (Bivalvia: Pectinidae) occur in Eur opean waters. Pecten maximus is largely an Atlantic species whilst Pecten j acobaeus is almost completely confined to Mediterranean waters despite slig ht overlap of distributions in the western Mediterranean. Genetic distances between these species were estimated using both allozyme electrophoresis a nd mitochondrial DNA PCR-RFLP and shown to be of a similar magnitude to int raspecific values, considerably lower than expected for congeneric species. These data are discussed in the light of recognised morphological differen ces, hybrid rearing trials and previous studies examining genetic distance by allozyme methodologies.