A scallop is a marine
Marine (ocean)
Marine is an umbrella term. As an adjective it is usually applicable to things relating to the sea or ocean, such as marine biology, marine ecology and marine geology...

 bivalve mollusk of the family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

The Pectinidae are a family of bivalve mollusks including the scallop and closely related to the clam and oyster. They are hermaphrodite, and the male gonads mature first. Pectinidae can live attached by means of a filament they secrete, or are simply recumbent. Their valves can propel them...

. Scallops are a cosmopolitan family, found in all of the world's oceans. Many scallops are highly prized as a food source. The brightly colored, fan-shaped shells of some scallops, with their radiating fluted pattern, are valued by shell collectors.

The name "scallop" is derived from the Old French escalope, which means "shell".
Like the true oysters (family Ostreidae
Ostreidae are the true oysters, and include most species that are commonly eaten under the name oyster. Pearl oysters are not true oysters and belong to the distinct order Pterioida....

), scallops have a central adductor
Adduction is a movement which brings a part of the anatomy closer to the middle sagittal plane of the body. It is opposed to abduction.-Upper limb:* of arm at shoulder ** Subscapularis** Teres major** Pectoralis major** Infraspinatus...

 muscle, and thus the inside of their shells has a characteristic central scar, marking the point of attachment for this muscle.