A scallop ( or /ˈskæləp/) is a marine bivalve mollusk of the family Pectinidae. 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" originated from the ancient Canaanite sea port Ascalon (modern city of Ashkelon, Israel).

Anatomy

Like the true oysters (family Ostreidae), scallops have a central adductor muscle, and thus the inside of their shells has a characteristic central scar, marking the point of attachment for this muscle. The adductor muscle of scallops is larger and more developed than that of oysters, because they are active swimmers; scallops are in fact the only migratory bivalve. Their shell shape tends to be highly regular, recalling one archetypal form of a seashell, and because of this pleasing geometric shape, the scallop shell is a common decorative motif.

Life habits

Most scallops are free-living, but some species can attach to a substrate by a structure called a byssus, or even be cemented to their substrate as adults (e.g. Hinnites spp.). A free-living scallop can swim, by rapidly opening and closing its shell. This method of locomotion is also a defense technique, protecting it from threatening predators. Some scallops can make an audible soft popping sound as they flap their shells underwater, leading one seafood vendor to dub them "singing scallops".

Reproductive cycle

The scallop family is unusual in that some members of the family are dioecious (males and females are separate), while other are simultaneous hermaphrodites (both sexes in the same individual) and a few are protoandrous hermaphrodites (males when young then switching to female). Red roe is that of a female, and white, that of a male. Spermatozoa and ova are released freely into the water during mating season and fertilized ova sink to the bottom. After several weeks, the immature scallop hatches and the larvae drift in the plankton until settling to the bottom again to grow, usually attaching by means of byssal threads. Some scallops, such as the Atlantic bay scallop Argopecten irradians are short lived, while others can live 20 years or more. Age can often be inferred by annuli, the concentric rings of their shells.

Gathering scallops

Scallops are most commonly harvested using scallop dredges or bottom trawls. Nowadays there is also a market for scallops harvested by divers. Scallops are hand-caught on the ocean floor, as opposed to being dragged across the sea floor by a dredge which causes them to collect sand. As a result, diver scallops tend to be less gritty. They can also be more ecologically friendly, as the harvesting method does not cause damage to undersea flora or fauna. In addition, the normal harvesting methods often mean delays of up to two weeks before the scallops arrive at market, which can cause the flesh to break down, and results in a much shorter shelf life.