However, the common name "scallop" is also sometimes applied to species in other closely related families within the superfamily Pectinoidea, which also includes the thorny oysters.

The majority of species, however, live recumbent on sandy substrates, and when they sense the presence of a predator such as a starfish, they may attempt to escape by swimming swiftly but erratically through the water using jet propulsion created by repeatedly clapping their shells together.

Owing to their widespread distribution, scallop shells are a common sight on beaches and are often brightly coloured, making them a popular object to collect among beachcombers and vacationers.

[citation needed] The model scallop shell consists of two similarly shaped valves with a straight hinge line along the top, devoid of teeth, and producing a pair of flat wings or "ears" (sometimes called "auricles", though this is also the term for two chambers in its heart) on either side of its midpoint, a feature which is unique to and apparent in all adult scallops.

They are attached to the visceral ganglia by long cerebral-visceral connectives, and to each other via a cerebral commissure that extends in an arch dorsally around the esophagus.

The cerebral ganglia control the scallop's mouth via the palp nerves and connect to statocysts which help the animal sense its position in the surrounding environment.

[16] However, the majority of scallops are free-living and can swim with brief bursts of speed to escape predators (mostly starfish) by rapidly opening and closing their valves.

Indeed, everything about their characteristic shell shape – its symmetry, narrowness, smooth and/ or grooved surface, small flexible hinge, powerful adductor muscle, and continuous and uniformly curved edge – facilitates such activity.

[16] Both jumping and swimming movements are very energy-intensive, and most scallops cannot perform more than four or five in a row before becoming completely exhausted and requiring several hours of rest.

So-called singing scallops are rumored to make an audible, soft popping sound as they flap their shells underwater (though whether or not this happens is open to some debate).

[18] Most species of the scallop family are free-living, active swimmers, propelling themselves through the water through the adductor muscles to open and close their shells.

[22] All possess a series of 100 blue eyes, embedded on the edge of the mantle of their upper and lower valves that can distinguish between light and darkness.

Though rather weak, their series of eyes can detect surrounding movement and alert precaution in the presence of predators, most commonly sea stars, crabs, and snails.

[6] Physiological fitness and exercise of scallops decrease with age due to the decline of cellular and especially mitochondrial function,[23] thus increasing the risk of capture and lowering rates of survival.

The properties of mitochondria from the phasic adductor muscle of Euvola ziczac varied significantly during their annual reproductive cycle.

Larvae stay in the water column for four to seven weeks before dissipating to the ocean floor, where they attach themselves to objects through byssus threads.

The relationship of the sponge to the scallop is characterized as a form of mutualism, because the sponge provides protection by interfering with adhesion of predatory sea-star tube feet,[30][31][32] camouflages Chlamys hastata from predators,[31] or forms a physical barrier around byssal openings to prevent sea stars from inserting their digestive membranes.

[8] The earliest species were divided into two groups, one with a nearly smooth exterior: Pleuronectis von Schlotheim, 1820, while the other had radial ribs or riblets and auricles: Praechlamys Allasinaz, 1972.

Its origin dates back to the Middle Triassic Period, approximately 240 million years ago;[8] in terms of diversity, it has been a thriving family to the present day.

[38] Evolution from its origin has resulted in a successful and diverse group: pectinids are present in the world's seas, found in environments ranging from the intertidal zone to the hadal depths.

The Pectinidae play an extremely important role in many benthic communities and exhibit a wide range of shell shapes, sizes, sculptures, and cultures.

[41] This family's earliest and most comprehensive taxonomic treatments were based on macroscopic morphological characters of the adult shells and represent broadly divergent classification schemes.

[42][29] Some level of taxonomic stability was achieved when Waller's studies in 1986, 1991, and 1993 concluded evolutionary relationships between pectinid taxa based on hypothesized morphological synapomorphies, which previous classification systems of Pectinidae failed to do.

Complicated factors can arise due to the presence of genetic polymorphisms in ancestral species and resultant lineage sorting.

With the shark population reduced – this apex predator in some places almost eliminated – the rays have been free to feed on scallops to greatly decrease their numbers.

[66][better source needed] In French cuisine, scallops are often quickly cooked in a hot buttered pan, sometimes with calvados and served with creamed leeks, or prepared in a white wine sauce.

[citation needed] Scallops are sometimes breaded, deep-fried, and served with coleslaw and french fries in the northeastern United States (either on their own or as part of a fisherman's platter).

[citation needed] In a sushi bar, hotategai (帆立貝, 海扇) is the traditional scallop on rice and, while kaibashira (貝柱) is more loosely used to include other shellfish species with round-shaped flesh (the adductor muscle), such as Atrina pectinata (帶子).

[85] One legend of the Way of St. James holds that the route was seen as a fertility pilgrimage, undertaken when a young couple desired to bear offspring.

[88][better source needed] The beach at Aldeburgh, Suffolk, England, features Maggi Hambling's steel sculpture, The Scallop, erected in 2003 as a memorial to the composer Benjamin Britten, who had a long association with the town.