A molecular approach to the systematics of the Antarctic scallop Adamussium colbecki

The taxonomy of Adamussium colbecki, the Antarctic scallop, is controversia l, and different views have been proposed. This species is included in the family Pectinidae by some authors, and in Propeamussiidae by others. In thi s study, the complete nucleotide sequence of the 18S subunit. of ribosomal DNA of A. colbecki was determined. The comparison of this new sequence with the corresponding sequences of Chlamys hastata, Chlamys islandica, Mimachl amys varia, Argopectin irradians, Pecten maximus, Crassadoma gigantea, and Placopecten magellanicus unequivocally showed that A. colbecki belongs to P ectinidae. No element supports the inclusion of A. colbecki in any other fa mily. These molecular data also suggest that the Chlamys group is polyphyle tic and that the distinction between the Pecten and the Chlamys groups has no obvious evolutionary basis.