|An edge-on view of a live scallop with the valves open, showing the mantle edges, the small blue pallial eyes and the pallial tentacles|
|Two scallop valves from Galicia (Spain), showing exterior and interior|
A scallop (// or //)[note 1] is a marine bivalve mollusks in the family Pectinidae. Scallops are a cosmopolitan family, found in all of the world's oceans though never in freshwater lakes or rivers. As members of the subclass pteriomorphia, along with the oysters, ark shells, file shells, shipworms, cockles, and saltwater mussels, they are considered a variety of saltwater clam. They are among the only bivalves to be regularly completely free-living and many species are capable of rapidly swimming short distances and even of migrating across the ocean floor.
Many scallops are highly prized as a food source; the name scallop is also applied to the meat of these animals when it is used as seafood. The brightly colored, symmetrical, fan-shaped shells of some scallops, with their radiating, often fluted patterns, are valued by shell collectors, and have been used since ancient times as motifs in art and design.
- 1 Anatomy
- 2 Locomotion
- 3 Seafood industry
- 4 As food
- 5 Symbolism
- 6 Notes
- 7 References
- 8 External links
There is very little variation in the internal arrangement of organs and systems within the scallops, and what follows can be taken to apply to the anatomy of any given scallop species.
The shell of a scallop consists of two sides or valves, a left valve and a right one, divided by a plane of symmetry. The animal normally rests on its right valve, and consequently this valve is sometimes flatter than the left (i.e., upper) valve. With the hinge of the two valves oriented as shown in the diagram, the left side of the image corresponds to the animal's morphological anterior or front, the right is the posterior or rear, the hinge is the dorsal or back/ top region, and the bottom corresponds to the ventral or (as it were) underside/ belly.
The shell of most scallops is designed to facilitate ease of movement during swimming while also providing protection from predators. Scallops with ridged valves have the advantage of the architectural strength provided by these ridges called ribs though they are somewhat costly in terms of weight. Scallops with two valves of the exact same size are referred to as equivalved, and those with one valve larger, smaller, or differently shapped than the other are termed inequivalved. Having valves of similar size and shape facilitates swimming, and most scallops are close to being equivalved. Many other bivalves, however, are also nearly or are fully equivalved-- it is the presence of a distinctive shell feature, a comb-like structure called a ctenolium located on the anterior edge of the right valve next to the byssal notch that defines the members of the scallop family. All scallops have this structure, and no other bivalve has an analogous one.
Like the true oysters (family Ostreidae), scallops have single central adductor muscles, thus the inside of their shells have characteristic central scars, marking the point of attachment for this muscle. The adductor muscle of scallops is larger and more developed than those of oysters, because they are active swimmers; some species of scallops are known to move en masse from one area to another. In scallops, the shell shape tends to be highly regular, and is commonly used as an archetypal form of a seashell.
Scallops have up to 100 simple brilliantly blue eyes arranged around the edges of each of their two mantles like strings of beads. They are reflector eyes, about one millimeter in diameter, that contain no actual blue pigment but with a retina that is more complex than those of other bivalves. Their eyes contain two retina types, one responding to light and the other to abrupt darkness, such as the shadow of a nearby predator. They cannot resolve shapes, but can detect changing patterns of light and motion. These reflector eyes are an alternative to those with a lens, where the inside of the eye is lined with mirrors which reflect the image to focus at a central point. The nature of these eyes means if one were to peer into the pupil of an eye, one would see the same image the organism would see, reflected back out. The scallop Pecten has up to 100 millimeter-scale reflector eyes fringing the edge of its shell. It detects moving objects as they pass successive eyes.
Scallops are filter feeders, and eat plankton. Incidentally, the plankton can include scallop larvae. They lack siphons. Water moves over a filtering structure, where food becomes trapped in mucus. Next, the cilia on the structure move the food toward the mouth. Then, the food is digested in the digestive gland, an organ sometimes misleadingly referred to as the "liver", but which envelops part of the esophagus, intestine, and the entire stomach. Waste is passed on through the intestine (the terminus of which, like that of many mollusks, enters and leaves the animal's heart) and exits via the anus.
Like all bivalves, scallops lack actual brains. Instead, their nervous system is controlled by three paired ganglia located at various points throughout their anatomy, the cerebral or cerebropleural ganglia, the pedal ganglia, and the visceral or parietovisceral ganglia. All are yellowish in color. The visceral ganglia are by far the largest and most extensive of the three, and occur as an almost-fused mass near the center of the animal. From these radiate all of the nerves which connect the visceral ganglia to the circumpallial nerve ring which loops around the mantle and connects to all of the scallop's tentacles and eyes. This nerve ring is so well developed that in some species it may be legitimately considered an additional ganglion. The visceral ganglia are also the origin of the branchial nerves which control the scallop's gills. The cerebral ganglia are the next largest set of ganglia, and lie distinct from each other a significant distance anterior to the visceral ganglia. 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 also connect to statocysts which help the animal sense its position in the surrounding environment. They are connected to the pedal ganglia by a short cerebral-pedal connective. The pedal ganglia, though not fused, are situated very close to each other near the midline. From the pedal ganglia the scallop puts out pedal nerves which control movement of and sensation in its muscular foot.
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 scallops hatch and the larvae, miniature transparent versions of the adults, 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 from annuli, the concentric rings of their shells.
The vast majority of adult bivalves are very slow-moving animals. But although it is believed that all scallops begin life with a byssus which attaches them to some form of substrate such as eel grass when they are very young, most lose this organ as they reach adulthood. As they become older, a few of these may then go on to cement themselves to a hard substrate (e.g. Chlamys distorta and Hinnites multirigosus). During their physical prime, however, the majority of scallops are free-living and can swim with surprising though 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. They often do this in spurts of several seconds before closing the shell entirely and sinking back to the bottom of their environment. Scallops are able to move through the water column either forward/ ventrally (termed swimming) by sucking water in through the space between their valves, an area called the gape, and ejecting it through small holes near the hinge line called exhalant apertures, or backward/ dorsally (termed jumping) by ejecting the water out the same way it came in (i.e., ventrally). A jumping scallop will usually land on the sea floor between each contraction of its valves, whereas a swimming scallop will stay in the water column for most or all of its contractions and will travel a much greater distance (though seldom at a height of more than one meter off the sea bed and seldom for a distance of greater than five meters). Both jumping to 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. Should a swimming scallop land on its left side, it is capable of flipping itself over to its right side via a similar shell-clapping movement called the righting reflex. So-called singing scallops can make an audible, soft popping sound as they flap their shells underwater. Other scallops can extend a "foot" from between their valves and by contracting it can burrow themselves into sand.
By far the largest wild scallop fishery is for the Atlantic sea scallop (Placopecten magellanicus) found off northeastern United States and eastern Canada. Most of the rest of the world's production of scallops is from Japan (wild, enhanced, and aquaculture), and China (mostly cultured Atlantic bay scallops).
Scallops are most commonly harvested using scallop dredges or bottom trawls. Recently, scallops harvested by divers, hand-caught on the ocean floor, have entered the marketplace. In contrast to scallops captured by a dredge across the sea floor, diver scallops tend to be less gritty. They are also more ecologically friendly, as the harvesting method does not cause damage to undersea flora or fauna. In addition, dredge-harvesting methods often result in 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.
The Tasman Bay area was closed to commercial scallop harvesting from 2009 to 2011 due to a decline in the numbers. In 2011, industry-funded research was conducted into scallop-harvesting patterns. Forest and Bird list scallops as "Worst Choice" in their Best Fish Guide for sustainable seafood species.
On the east coast of the United States, over the last 100 years, the populations of bay scallops have greatly diminished due to several factors, but probably is mostly due to reduction in sea grasses (to which bay scallop spat attach) caused by increased coastal development and concomitant nutrient runoff. Another possible factor is reduction of sharks from overfishing. A variety of sharks used to feed on rays, which are a main predator of bay scallops. With the shark population reduced — in some places almost eliminated — the rays have been free to feed on scallops to the point of greatly decreasing their numbers. By contrast, the Atlantic sea scallop (Placopecten magellanicus) is at historically high levels of abundance after recovery from overfishing.
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Scallops are characterized by having two types of meat in one shell: the adductor muscle, called "scallop", which is white and meaty, and the roe, called "coral", which is red or white and soft. Sometimes, markets sell scallops already prepared in the shell, with only the adductor muscle intact. Outside the U.S., the scallop is often sold whole. In Galician cuisine, scallops are baked with bread crumbs, ham, and onions. In the UK and Australia, they are available both with and without the roe. The roe is also usually eaten. Scallops without any additives are called "dry packed", while scallops that are treated with sodium tripolyphosphate (STPP) are called "wet packed". STPP causes the scallops to absorb moisture prior to the freezing process, thereby increasing the weight. The freezing process takes about two days.
In Japanese cuisine, scallops may be served in soup or prepared as sashimi or sushi. Dried scallop is known in Cantonese Chinese cuisine as conpoy (乾瑤柱, 乾貝, 干貝). In a sushi bar, hotategai (帆立貝, 海扇) is the traditional scallop on rice, and while kaibashira (貝柱) may be called scallops, it is actually the adductor muscle of any kind of shellfish, e.g. mussels, oysters, or clams.
Scallops have lent their name to the culinary term 'scalloped', which originally referred to seafood creamed and served hot in the shell. Today, it means a creamed casserole dish such as scalloped potatoes, which contains no seafood at all. Smoked scallops are sometimes served as appetizers or as an ingredient in the preparation of various dishes and appetizers.
Shell of Saint James
The scallop shell is the traditional emblem of James, son of Zebedee, and is popular with pilgrims on the Way of St James to the apostle's shrine at Santiago de Compostela in Galicia (Spain). Medieval Christians making the pilgrimage to his shrine often wore a scallop shell symbol on their hat or clothes. The pilgrim also carried a scallop shell with him, and would present himself at churches, castles, abbeys etc., where he could expect to be given as much sustenance as he could pick up with one scoop. Probably he would be given oats, barley, and perhaps beer or wine. Thus even the poorest household could give charity without being overburdened.
The association of Saint James with the scallop can most likely be traced to the legend that the apostle once rescued a knight covered in scallops. An alternative version of the legend holds that while St. James' remains were being transported to Galicia (Spain) from Jerusalem, the horse of a knight fell into the water, and emerged covered in the shells. Indeed, in French the animal (as well as a popular preparation of it in cream sauce) is called coquille St. Jacques. In German, they are Jakobsmuscheln — literally "James mussels". Curiously the Linnaeus name Pecten jacobeus refers to the Mediterranean scallop, while the scallop endemic of Galicia is called Pecten maximus due to its bigger size.
The scallop shell is represented in the decoration of churches named after St. James, such as in St James' Church, Sydney, where it appears in a number of places, including in the mosaics on the floor of the chancel. When referring to St James, the scallop shell is represented with convex perspective. Referring to Venus the perspective is concave.
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Throughout antiquity, scallops and other hinged shells have symbolized the feminine principle. Outwardly, the shell can symbolize the protective and nurturing principle, and inwardly, the "life-force slumbering within the Earth", an emblem of the vulva.
Many paintings of Venus, the Roman goddess of love and fertility, included a scallop shell in the painting to identify her. This is evident in Botticelli's classically inspired The Birth of Venus (jocularly nicknamed 'Venus on the half-shell').
One legend of the Way of St. James holds that the route was seen as a sort of fertility pilgrimage, undertaken when a young couple desired to bear offspring. The scallop shell is believed to have originally been carried, therefore, by pagans as a symbol of fertility.
Alternatively, the scallop resembles the setting sun, which was the focus of the pre-Christian Celtic rituals of the area. To wit, the pre-Christian roots of the Way of St. James was a Celtic death journey westwards towards the setting sun, terminating at the End of the World (Finisterra) on the "Coast of Death" (Costa da Morte) and the "Sea of Darkness" (i.e., the Abyss of Death, the Mare Tenebrosum, Latin for the Atlantic Ocean, itself named after the Dying Civilization of Atlantis). The reference to St. James rescuing a "knight covered in scallops" is therefore a reference to St. James healing, or resurrecting, a dying (setting sun) knight. Similarly, the notion of the "Sea of Darkness" (Atlantic Ocean) disgorging St. James' body, so that his relics are (allegedly) buried at Santiago de Compostella on the coast, is itself a metaphor for "rising up out of Death", that is, resurrection.
The scallop shell symbol found its way into heraldry as a badge of those who had been on the pilgrimage to Compostela, although later it became a symbol of pilgrimage in general. Winston Churchill and Diana, Princess of Wales' family, the Spencer family coat of arms includes a scallop, as well as both of Diana's sons Prince William, Duke of Cambridge and Prince Harry's personal coats of arms; also Pope Benedict XVI's personal coat of arms includes a scallop; another example is the surname Wilmot and also John Wesley's (which as a result the scallop shell is used as an emblem of Methodism). However, charges in heraldry do not always have an unvarying symbolic meaning, and there are cases of arms in which no family member went on a pilgrimage and the occurrence of the scallop is simply a pun on the name of the armiger (as in the case of Jacques Coeur), or for other reasons.
State shell of New York
In design, 'scalloped edges' or 'ridges' refers to a wavy pattern reminiscent of the edge of a scallop's shell.
On the beach at Aldeburgh, Suffolk, England, is Maggi Hambling's metal sculpture, The Scallop, erected in 2003 as a memorial to the composer Benjamin Britten, who had a long association with the town.
- from Old French escalope, meaning "shell". Earlier versions of this article claim the word scallop originated from the ancient Canaanite sea port Ascalon (modern city of Ashkelon, Israel). This error is probably due to the close proximity of the words scallion and scallop in many dictionaries. The word scallion has origins in Ascalon (see the same link cited at the beginning of this reference). Unfortunately, as of August 2009, Google search results for ascalon scallop indicate over 3300 pages now cite the incorrect information from the earlier version of this article.
||This article includes a list of references, but its sources remain unclear because it has insufficient inline citations. (February 2008)|
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|Look up scallop in Wiktionary, the free dictionary.|
|Wikispecies has information related to: Pectinidae|
- Alaska Department of Fish and Game - scallop page
- NOAA Fisheries: Northeast Fisheries Science Center - Research on Bay Scallop Aquaculture and Enhancement
- Delaware Sea Grant, University of Delaware - scallop page
- Classification of Pectinoidea (Propeamussiidae and Pectinidae) - includes partly different genera, with subfamilies and tribes.
- "Too Few Jaws: Shark declines let rays overgraze scallops", Science News, March 31, 2007