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Scallop eyes.jpg
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
Cuncha GFDL Galicia3.jpg
Two scallop valves from Galicia (Spain), showing exterior and interior
Scientific classification
Rafinesque, 1815

See Pectinidae

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For verb senses, see Scalloping. For potato scallops, see Potato cake. For the cut of meat, see Escalope. For the scallop shell moth, see Rheumaptera undulata.
Scallop eyes.jpg
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
Cuncha GFDL Galicia3.jpg
Two scallop valves from Galicia (Spain), showing exterior and interior
Scientific classification
Rafinesque, 1815

See Pectinidae

A scallop (/ˈskɒləp/ or /ˈskæləp/; from Old French escalope, meaning "shell"[1]) is a common name applied to many species of marine bivalve mollusks in the family Pectinidae, the scallops. Scallops are a cosmopolitan family, found in all of the world's oceans.

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, fan-shaped shells of some scallops, with their radiating, fluted patterns, are valued by shell collectors, and have been used since ancient times as motifs in art and design.



Anatomical diagram of a typical hermaphroditic scallop with the left (i.e., upper) valve removed: the interior of the shell is shown in black for contrast.

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".[2]

Muscular system[edit]

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.


A live opened scallop showing the internal anatomy: The pale orange circular part is the adductor muscle; the darker orange curved part is the "coral", a culinary term for the ovary.

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.[3][4] 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.[5] 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.[5] 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.[5]

Digestive system[edit]

Most 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.

Nervous system[edit]

Like all bivalves, scallops lack actual brains. Instead, their nervous system is controlled by three paired ganglia located at various points throughout their anatomy. These are termed the cerebral ganglia, the pedal ganglia, and the visceral ganglia. All are yellowish in color; the visceral ganglia are by far the largest and most extensive of the three.


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.

Life habits[edit]

Icelandic scallop Chlamys islandica, equiped with activity electrodes.

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.). Other scallops can extend a "foot" from between their valves. By then contracting the foot, they can burrow themselves deeper into sand. A free-living scallop can swim by rapidly opening and closing its shell. This method of locomotion is also a defensive technique, protecting it from threatening predators. So-called singing scallops can make an audible, soft popping sound as they flap their shells underwater.

The daily and yearly behavior of fixed scallop is quite complex although their valves stay open most of the time and very rare full closures do occur. Only the distance between them varies to leave their lips open or closed. A website devoted to molluscan behavior, MolluSCAN eye, allows to see daily behavior of Icelandic scallops in various Arctic places (Ny Alesund, Svalbard; fjord of Tromso, Norway; Bay of Dalnie Zelentsy, Barents Sea, Russia).

Seafood industry[edit]

Wild fisheries[edit]

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.[6] 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,[citation needed] which can cause the flesh to break down, and results in a much shorter shelf life.


Main article: Scallop aquaculture

In 2005, China accounted for 80% of the global scallop and pecten catch, according to an FAO study.[7] Outside of China, Russia remained the industry leader.


New Zealand[edit]

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.[8]

United States[edit]

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.

As food[edit]

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.[9] 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.[10] 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.[11]


Portrait by Carlo Crivelli, c. 1480

Shell of Saint James[edit]

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.[citation needed] 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.

Fertility symbol[edit]

Aphrodite in a sea shell, from Amisos, now in the Louvre

Throughout antiquity, scallops and other hinged shells have symbolized the feminine principle.[12] Outwardly, the shell can symbolize the protective and nurturing principle, and inwardly, the "life-force slumbering within the Earth",[13] an emblem of the vulva.[14][15]

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'[16]).

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.[17][18]

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).[19] 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.[20]


A scallop shell as a heraldic device on a German coat of arms

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[edit]

The state of New York in the United States made the bay scallop (Argopecten irradians) its state shell in 1988.[21]


In design, 'scalloped edges' or 'ridges' refers to a wavy pattern reminiscent of the edge of a scallop's shell.


The energy corporation Royal Dutch Shell derives its highly recognizable logo from the scallop species Pecten maximus.

Britten Memorial[edit]

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.


  1. ^ Note: 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.
  2. ^ Drew, Gilman Arthur (1906), The Habits Anatomy, and Embryology of the Giant Scallop: (Pecten Tenuicostatus, Mighels), pp. 5–6 
  3. ^ Eyes detect changing movement patterns: queen scallop - Ask Nature - the Biomimicry Design Portal: biomimetics, architecture, biology, innovation inspired by nature, industria...
  4. ^ Land MF and Fernald RD (1992) "The evolution of eyes" Annual review of neuroscience, 15: 1–29.
  5. ^ a b c Land, M F; Fernald, R D (1992). "The Evolution of Eyes". Annual Review of Neuroscience 15: 1–29. doi:10.1146/ PMID 1575438. 
  6. ^ Walker, Margaret (1991). "What price Tasmanian scallops? A report of morbidity and mortality associated with the scallop diving season in Tasmania 1990.". South Pacific Underwater Medicine Society Journal 21 (1). Retrieved 2013-07-16. 
  7. ^ China catches 1 m tonnes of scallops and pectens in 2005
  8. ^ Scallops | Forest and Bird
  9. ^
  10. ^ (Rombauer 1964).
  11. ^ AndyTalk: Beyond Lox - Smoked Seafood Hold the Bagels | Phoenix New Times
  12. ^ Salisbury JE (2001) Women in the ancient world, p. 11. ABC-CLIO, ISBN 978-1-57607-092-5.
  13. ^ Fontana D (1994) The secret language of symbols: a visual key to symbols and their meanings, pp. 88, 103. Chronicle Books, ISBN 978-0-8118-0462-2.
  14. ^ Gutzwiller K (1992) "The Nautilus, the Halycon, and Selenaia: Callimachus's Epigram 5 Pf.= 14 G.-P.", Classical Antiquity, 11(2): 175-193.
  15. ^ Johnson B (1994) Lady of the beasts: the Goddess and her sacred animals, p. 230. Inner Traditions/Bear & Company, ISBN 978-0-89281-523-4.
  16. ^ Porter D and Prince D (2009) Frommer's Italy 2010, p. 273. Frommer's, ISBN 978-0-470-47069-5.
  17. ^ Slavin S (2003) "Walking as Spiritual Practice: The Pilgrimage to Santiago de Compostela" Body and Society 9(1):18. doi 10.1177/1357034X030093001
  18. ^ Gauding M (2009) The Signs and Symbols Bible: The Definitive Guide to Mysterious Markings, Page 169. Sterling Publishing Company. ISBN 978-1-4027-7004-3
  19. ^ Thomas, Isabella. "Pilgrim's Progress". Europe in the UK. European Commission.
  20. ^ Pinkham MA (2004) Guardians Of The Holy Grail: The Knights Templar, John The Baptist, And The Water Of Life Page 235. Adventures Unlimited Press. ISBN 978-1-931882-28-6
  21. ^ "New York State Shell: Bay Scallop". State Symbols USA. Retrieved 2012-05-24. 

External links[edit]