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 are a cosmopolitan family of bivalves, found in all of the world’s oceans, though never in freshwater. They are one of very few groups of bivalves to be primarily “free-living”; many species are capable of rapidly swimming short distances and even of migrating some distance across the ocean floor. A small minority of scallop species live cemented to rocky substrates as adults, while others are more simply attached by means of a filament they secrete called a byssal thread. The majority of species, however, live recumbent on sandy substrates, and when they sense the presence of a predator such as a starfish, they are able to escape by swimming swiftly but erratically through the water using a form of jet propulsion created by repeatedly clapping their shells together. Scallops have a well-developed nervous system, and unlike most other bivalves they have numerous simple eyes situated around the edge of their mantles.
Many species of scallops are highly prized as a food source, and some are farmed as aquaculture. The word “scallop” is also applied to the meat of these bivalves when it is sold as seafood. In addition the name “scallop” is used as part of the name of dishes based on the meat of scallops, and is even applied to some dishes not containing scallop at all but which are prepared in a similar fashion. The brightly colored, symmetrical, fan-shaped shells of scallops with their radiating and often fluted sculpture are valued by shell collectors, and have been used since ancient times as motifs in art, architecture and design.
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.
Text from Wikipedia