Scallop (/ˈskɒləp/ or /ˈskæləp/) is a common name that is primarily applied to any one of numerous species of saltwater clams or marine bivalve mollusks in the taxonomic family Pectinidae, the scallops. However, the common name "scallop" is also sometimes applied to species in other closely related families within the superfamily Pectinoidea. Scallops do produce pearls, though the pearls do not have the buildup of layers, or “nacre”, and may not have luster or iridescence. They can be dull, small and of varying color, but there are exceptions that are appreciated for their aesthetic qualities.