Abstract
An elliptic Fourier analysis was carried out on shell outlines in 63 species of the Pectinidae (Bivalvia). Fourier coefficients and their principal components were used to compare shell shapes among taxonomic subgroups and life habits. This study reveals differences in shell outline between the tribes of byssate and free-living pectinids. Byssally attached species of the Pectininae have more rounded and equilateral shell outlines than those of the byssate Chlamydini and Mimachlamydini. Free-living pectinids generally possess circular and equilateral shells, except for some species of the Decatopectinini. This study suggests that the change of life habit from byssally attached to free living required Chlamydinae to modify their shell outlines considerably, whereas only a minor modification of the outline enabled the byssate Pectininae to adapt to free-living habits. Patinopecten, which represents the only free-living scallop in the Chlamydinae, has a shell outline with a smaller aspect ratio than most of the free-living Pectininae. This suggests that a vestige of the oblong shell shape of typical Chlamydini still remains in the shell of Patinopecten, showing a phylogenetic constraint.
