Overview

Brief Summary

There are at least 250 species in the scallop family. Most scallops can swim by opening and closing their shells. Others stay fixed in one spot. Scallops have up to 100 eyes. The eyes can only distinguish between light and darkness, but they help scallops avoid predators.

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Evolution and Systematics

Functional Adaptations

Functional adaptation

Shell resists cracking: scallop
 

The shell of a scallop resists cracking via composite structure.

   
  "But there's yet another and perhaps even better way to keep cracks from propagating disastrously. It consists of making a material of at least two components, one stiffer than the other. If a crack runs through a little fiber of stiff material and then reaches an unstiff (compliant) component, the latter will give a little, accommodate the crack, and reduce the force concentration at the tip of the crack (fig. 16.10). Result--the crack stops…Organisms don't use pure metals, and they use composites for all their rigid and most of their pliant materials…They inevitably divide their stiff stuff into small pieces that form components of composites…You can drill a hole in a scallop shell with little worry that it might shatter…it's not as brittle as you might think." (Vogel 2003:339-340)
  Learn more about this functional adaptation.
  • Steven Vogel. 2003. Comparative Biomechanics: Life's Physical World. Princeton: Princeton University Press. 580 p.
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Molecular Biology and Genetics

Molecular Biology

Statistics of barcoding coverage

Barcode of Life Data Systems (BOLD) Stats
                                        
Specimen Records:442Public Records:219
Specimens with Sequences:237Public Species:30
Specimens with Barcodes:234Public BINs:27
Species:63         
Species With Barcodes:38         
          
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Barcode data

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Locations of barcode samples

Collection Sites: world map showing specimen collection locations for Pectinidae

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Genomic DNA is available from 1 specimen with morphological vouchers housed at University of the Philippines-Diliman, Marine Science Institute
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Genomic DNA is available from 4 specimens with morphological vouchers housed at Museum of Tropical Queensland and Ocean Genome Legacy
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Wikipedia

Pectinidae

The Pectinidae (from the Latin pecten meaning comb), common name scallops, are a family of saltwater bivalve mollusks. They are hermaphrodites, and the male gonads mature first. Numerous species of various sizes occur in all of the oceans, and a number species are of commercial importance as food species.

A small minority of pectinid species live cemented to rocky substrates as adults. Some others species are more simply attached, by means of a filament they secrete. The majority of species, however, are recumbent on sandy substrates, but when they sense the presence of a predator such as a starfish, they are able to escape by swimming swiftly but erratically through the water using a form of jet propulsion created by repeatedly clapping the valves of their shells together.

Pectinids have numerous simple eyes situated around the edges of their mantles.

Shell morphology[edit]

In general, shells of the Pectinidae consist of two valves which are circular to broadly ovate with the right valve usually more inflated than the left valve. The valves are narrower and pointed at the umbones, which have flattened triangular extensions on both sides, known as auricles or ears. The upper edge of the ears forms a somewhat straight hinge line. The umbones project only slightly above this line. Most Pectinidae have radial ribs and concentric ridges, although a few are smooth. The ctenolium, a key shell feature, separates the Pectinidae from all other families.

Distribution and habitat[edit]

Pectinidae inhabit all the oceans of the world, with the largest number of species living in the Indo-Pacific region. Most species live in relatively shallow waters from the low tide line to 100 meters, while others prefer much deeper water. Although some species only live in very narrow environments, most are opportunistic and can live under a wide variety of conditions. Pectinidae can be found living within, upon, or under either rocks, coral, rubble, sea grass, kelp, sand, or mud. Most adult specimens are either byssally attached or cemented to a substrate, while others are free swimmers.

Motility and behavior[edit]

Most species of the Pectinidae family are free-living active swimmers, propelling themselves through the water through the use of the adductor muscles to open and close their shells. Swimming occurs by the clapping of valves for water intake. Closing the valves propels water with strong force near the hinge via the velum, a curtain-like fold of the mantle that directs water expulsion around the hinge. Pectinidae swim in the direction of the valve opening, unless the velum directs an abrupt change in course direction.[1][2]

Other species of Pectinidae can be found on the ocean floor attached to objects by byssal threads. Byssal threads are strong, silky fibers extending from the muscular foot, used to attach to a firm support, such as a rock. Some can also be found on the ocean floor, moving with the use of an extendable foot located between their valves or burrowing themselves in the sand by extending and retracting their feet.

Pectinidae are highly sensitive to shadows, vibrations, water movement, and chemical stimuli.[3] 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. They serve as a vital defense mechanism for avoiding predators. 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.

Physiological fitness and exercise of Pectinidae decreases with age due to the decline of cellular and especially mitochondrial function,[4] thus increasing the risk of capture and lowering rates of survival. Older individuals show lower mitochondrial volume density and aerobic capacity, as well as decreased anaerobic capacity construed from the amount of glycogen stored in muscle tissue.[5] Environmental factors, such as changes in oxidative stress parameters, can inhibit the growth and development of Pectinidae.[6]

Seasonal changes in temperature and food availability have shown to affect muscle metabolic capabilities. The properties of mitochondria from the phasic adductor muscle of Euvola ziczac varied significantly during their annual reproductive cycle. Summer Pectinidae in May have lower maximal oxidative capacities and substrate oxidation than any other times in the year. This phenomenon is due to lower protein levels in adductor muscles.[7]

Mutualism[edit]

Chlamys hastate frequently carries epibionts like sponges and barnacles on its shell. The scallop-shell relationship is characterized as a form of mutualism. The sponge provides protection by interfering with adhesion of predatory sea-star tube feet,[8][9][10] camouflages Chlamys hastate from predators,[11] or forms a physical barrier around byssal openings to prevent sea stars from inserting their digestive membranes.[12] Sponge encrustation protects C. hastate from barnacle larvae settlement, serving as a protection from epibionts that increase susceptibility to predators. Thus, barnacle larvae settlement will occur more frequently on sponge-free shells than sponge-encrusted shells.

In fact, barnacle encrustation negatively influences swimming in C. hastata. Those swimming with barnacle encrustation require more energy and show a detectable difference in anaerobic energy expenditure than those without encrustation.[13] In the absence of barnacle encrustation, they swim significantly longer, travel further, and attain greater elevation.

Lifecycle and growth[edit]

Many Pectinidae are hermaphrodites (having female and male organs simultaneously), altering their gender throughout their lives, while others exist as dioecious species, having a definite gender. In this case, males are distinguished by roe containing white testes and females with roe containing orange ovaries. At the age of two, they usually become sexually active, but do not contribute significantly to egg production until the age of four. The process of reproduction takes place externally through spawning, in which eggs and sperm are released into the water. Spawning typically occurs in late summer and early autumn; spring spawning may also take place in the mid-Atlantic Bright.[14] The females of Pectinidae are highly fecund, capable of producing hundreds of millions of eggs per year.[15]

Once an egg is fertilized, it is then planktonic, which is a collection of microorganisms that drift abundantly in fresh or salt water. Larvae stay in the water column for the next four to seven weeks before dissipating to the ocean floor, where they attach themselves to objects through byssus threads. Byssus is eventually lost with adulthood, transitioning Pectinidae into free swimmers. There is rapid growth within the first several years, with an increase of 50 to 80% in shell height and quadrupled size in meat weight and reach commercial size at about four to five years of age.[16] The lifespans of some Pectinidae have been known to extend over 20 years.[17]

Fossil record[edit]

Fossil Pectinidae from East Timor

The fossil history of Pectinidae is rich in species and specimens. The earliest known records of true Pectinidae (those with a ctenolium) can be found from the Triassic period over 200 million years ago.[18] 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.[19] Fossil records also indicate the existence of Pectinidae has been unstable at times; from being the most speciose family of the Mesozoic era, to almost disappearing completely by the end of the Cretaceous period. Survivors evolved rapidly during the Tertiary period. Nearly 7,000 species and subspecies names have been introduced for both fossil and recent Pectinidae.

Taxonomy and list of genera[edit]

More than 30 genera and around 350 species are in the family Pectinidae. Raines and Poppe[20] list nearly 900 species names, but most of these are considered either questionable or invalid. They mention over 50 genera and around 250 species and subspecies. While species are generally well circumscribed, their attribution to subfamilies and genera is sometimes equivocal, and information about phylogeny and relationships of the species is minimal, not the least because most work has been based on adult morphology.[21]

Evolution[edit]

The family Pectinidae is the most diversified of the pectinoideans in present-day oceans. It is one of the largest marine bivalve families and contains 300 extant species in 60 genera.[22] Its origin dates back to the Middle Triassic Period, approximately 240 million years ago, and has been a thriving family to present day. 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 plays an extremely important role in many benthic communities and exhibits a wide range of shell shape, sizes, sculpture, and culture.[23]

The earliest and most comprehensive taxonomic handlings of the family are based on macroscopic morphological characters of the adult shells and represent broadly divergent classification schemes.[24][25] 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.[26][27][28] He created three Pectinidae subfamilies: Camptonectinidae, Chlamydinae and Pectininae.

The framework of its phylogeny shows that repeated life habit states derive from evolutionary convergence and parallelism.[29][30] Studies have determined the Pectinidae family is monophyletic, developing from a single common ancestor. The direct ancestors of Pectinidae were scallop-like bivalves of the family Entoliidae.[31] Entoliids had auricles and byssal notch only at youth, but they did not have a ctenolium, a comb-like arrangement along the margins of the byssal notch in Pectinidae. The ctenolium is the defining feature of the modern family Pectinidae and is a characteristic that has evolved within the lineage.[32]

Recently, Puslednik et al. identified considerable convergence of shell morphology in a subset species of gliding Pectinidae, which suggests iterative morphological evolution may be more prevalent in the family than previously believed.[33]

There have been a number of efforts to address phylogenetic studies. Only three have assessed more than 10 species[34][35][36] and only one has included multiple outgroups.[37] Nearly all previous molecular analyses of the Pectinidae have only utilized mitochondrial data. Phylogenies based only on mitochondrial sequence data do not always provide an accurate estimation on the species tree. Complicated factors can arise due to the presence of genetic polymorphisms in ancestral species and resultant lineage sorting.[38][39]

In molecular phylogenies of the Bivalvia, both the Spondylidae and the Propeamussiidae have been resolved as sister to the Pectinidae.[40][41] A useful strategy would be to include outgroup species from two or more closely related families.

Genera[edit]

Family Pectinidae

Gallery[edit]

References[edit]

  1. ^ Cheng, J.-Y.; Davison, I. G.; Demont, M. E. (1996). "Dynamics and energetics of scallop locomotion". Journal of Experimental Biology 199 (9): 1931–1946. 
  2. ^ Joll, L.M. (1989). Swimming behavior of the saucer scallop Amusium balloti (Mollusca: Pectinidae). Marine Biology. pp. 299–305. 
  3. ^ Land, M.F. (1966). "Activity in the optic nerve of Pecten maximus in response to changes in light intensity, and to pattern and movements in optical environment". Journal of Experimental Biology 45 (1): 83–99. 
  4. ^ Philipp, E.E.R.; Schmidt, M.; Gsottbauer, C.; Sänger, A. M.; Abele, D. (2008). "Size- and age- dependent changes in adductor muscle swimming physiology of the scallop Aequipecten opercularis". Journal of Experimental Biology 211 (15): 2492–2501. doi:10.1242/jeb.015966. 
  5. ^ Philipp, E.E.R.; Schmidt, M.; Gsottbauer, C.; Sänger, A. M.; Abele, D. (2008). "Size- and age- dependent changes in adductor muscle swimming physiology of the scallop Aequipecten opercularis". Journal of Experimental Biology 211 (15): 2492–2501. doi:10.1242/jeb.015966. 
  6. ^ Guerra, C.; Zenteno-Savín, T.; Maeda-Martínez, A. N.; Abele, D.; Philipp, E. E. R. (2013). "The effect of predator exposure and reproduction on oxidative stress parameters in the Catarina scallop Argopecten ventricosus". Comparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology 165 (1): 89–96. doi:10.1016/j.cbpa.2013.02.006. 
  7. ^ Boadas, M.A.; Nusetti, O.; Mundarain, F. (1997). "Seasonal variation in the properties of muscle mitochondria from the tropical scallop Euvola (Pecten) ziczac". Marine Biology 128 (2): 247–255. doi:10.1007/s002270050089. 
  8. ^ Bloom, S. (1975). "The motile escape response of a sessile prey: a sponge-scallop mutualism". Journal of Experimental Biology and Ecology 17 (3): 311–321. doi:10.1016/0022-0981(75)90006-4. 
  9. ^ Pitcher, C.R.; Butler, A.J. (1987). "Predation by asteroids, escape response, and morphometrics of scallops with epizoic sponges". Journal of Experimental Marine Biology and Ecology 112 (3): 233–249. doi:10.1016/0022-0981(87)90071-2. 
  10. ^ Forester, A.J. (1979). "The association between the sponge Halichondria panicea (Pallas) and scallop Chlamys varia (L.): a commensal protective mutualism". Journal of Experimental Marine Biology and Ecology 36 (1): 1–10. doi:10.1016/0022-0981(79)90096-0. 
  11. ^ Pitcher, C.R.; Butler, A.J. (1987). "Predation by asteroids, escape response, and morphometrics of scallops with epizoic sponges". Journal of Experimental Marine Biology and Ecology 112 (3): 233–249. doi:10.1016/0022-0981(87)90071-2. 
  12. ^ Forester, A.J. (1979). "The association between the sponge Halichondria panicea (Pallas) and scallop Chlamys varia (L.): a commensal protective mutualism". Journal of Experimental Marine Biology and Ecology 36 (1): 1–10. doi:10.1016/0022-0981(79)90096-0. 
  13. ^ Donovan, D.; Bingham, B.; Farren, H.; Gallardo, R.; Vigilant, V. (2002). "Effects of sponge encrustation on the swimming behaviour energetics and morphometry of the scallop Chlamys hastata". Journal of the Marine Biological Association of the United Kingdom 82 (3): 469–476. doi:10.1017/s0025315402005738. 
  14. ^ Hart, D.R.; Chute, A.S. (2004). "Essential Fish Habitat Source Document: Sea Scallop, Placopecten magellanicus, Life History and Habitat Characteristics". NOAA Tech Memo NMFS NE-189. 
  15. ^ Hart, D.R.; Chute, A.S. (2004). "Essential Fish Habitat Source Document: Sea Scallop, Placopecten magellanicus, Life History and Habitat Characteristics". NOAA Tech Memo NMFS NE-189. 
  16. ^ Hart, D.R.; Chute, A.S. (2004). "Essential Fish Habitat Source Document: Sea Scallop, Placopecten magellanicus, Life History and Habitat Characteristics". NOAA Tech Memo NMFS NE-189. 
  17. ^ "Scallop Aquaculture". College of Marine Science. 
  18. ^ Treatise on Invertebrate Paleontology Geological Society of America, Kansas, Part N, Vol. I (1969) p. N348.
  19. ^ Waller, T. R. (1993): The evolution of "Chlamys" (Mollusca: Bivalvia: Pectinidae) in the tropical western Atlantic and eastern Pacific. American Malacological Bulletin 10 (2): 195-249.
  20. ^ Raines, B. K. & Poppe, G. T. (2006): The Family Pectinidae. In: Poppe, G. T. & Groh, K.: A Conchological Iconography. 402 pp., 320 color plts., ConchBooks, Hackenheim, ISBN 3-925919-78-3.
  21. ^ Barucca, M., Olmo, E., Schiaparelli, S. & Canapa, A. (2004): Molecular phylogeny of the family Pectinidae (Mollusca: Bivalvia)
  22. ^ Waller, T.R. (2006a). New phylogenies of the Pectinidae (Mollusca: Bivalvia): Reconciling morphological and molecular approaches. Scallops: biology, ecology and aquaculture II (Ed. S. E. Shumway): Elsevier, Amsterdam. pp. 1–44. 
  23. ^ Brand, A.R. (2006). "Scallop ecology: distributions and behavior". Scallops: Biology, Ecology and Aquaculture 35: 651–744. doi:10.1016/S0167-9309(06)80039-6. 
  24. ^ Waller, T.R. (1972). The functional significance of some shell micro-structures in the Pectinacea. Paleontology: International Geological Congress. pp. 48–56. 
  25. ^ Habe, T. (1977). Systematics of Mollusca in Japan. Bivalvia and Scaphopoda. 
  26. ^ Waller, T.R. (1986). "A new genus and species of scallop (Bivalvia: Pectinidae) from off Somalia, and the definition of a new tribe Decatopectinini". Nautilus 100 (2): 39–46. 
  27. ^ Waller, T.R. (1991). Evolutionary relationships among commercial scallops (Mollusca: Bivalvia: Pectinidae). Scallops: Biology, Ecology and Aquaculture. pp. 1–73. 
  28. ^ Waller, T.R. (1993). "Waller, T. R. (1993). The evolution of "Chlamys" (Mollusca: Bivalvia: Pectinidae) in the tropical western Atlantic and eastern Pacific". American Malacological Bulletin 10 (2): 195–249. 
  29. ^ Alejandrino, A.; Puslednik, L.; Serb, J. M. (2011). "Convergent and parallel evolution in life habit of the scallops". BMC Evolutionary Biology 11 (1): 164. doi:10.1186/1471-2148-11-164. PMC 3129317. 
  30. ^ Waller, T.R. (2007). "The evolutionary and biogeographic origins of the endemic Pectinidae (Mollusca: Bivalvia) of the Galápagos Islands". Journal of Paleontology 81 (5): 929–950. doi:10.1666/pleo05-145.1. 
  31. ^ Dijkstra, H.H.; Maestrati, P. (2012). "Pectinoidea (Mollusca, Bivalvia, Propeamussiidae, Cyclochlamydidae n. fam., Entoliidae and Pectinidae) from the Vanuatu Archipelago". Zoosystema 34 (2): 389–408. doi:10.5252/z2012n2a12. 
  32. ^ Waller, T.R. (1984). "The ctenolium of scallop shells: functional morphology and evolution of a key family-level character in the Pectinacea (Mollusca: Bivalvia)". Malacologia 25 (1): 203–219. 
  33. ^ Puslednik, L.; Serb, J.M. (2008). "Molecular phylogenetics of the Pectinidae (Mollusca: Bivalvia) and the effect of outgroupselection and increased taxon sampling on tree topology". Molecular Phylogenetics and Evolution 31 (1): 89–95. doi:10.1016/j.ympev.2008.05.006. 
  34. ^ Barucca, M.; Olmo, E.; Schiaparelli, S.; Capana, A. (2004). "Molecular phylogeny of the family Pectinidae (Mollusca: Bivalvia) based on mitochondrial 16S and 12S rRNA genes". Molecular Phylogenetics and Evolution 31 (1): 89–95. doi:10.1016/j.ympev.2003.07.003. 
  35. ^ Matsumoto, M.; Hayami, I. "Phylogenetic analysis of the family Pectinidae (Bivalvia) based on mitochondrial cytochrome C oxidase subunit". Journal of Molluscan Studies 66 (4): 477–488. doi:10.1093/mollus/66.4.477. 
  36. ^ Saavedra, C.; Peña, J.B (2006). "Phylogenetics of American scallops (Bivalvia: Pectinidae) based on partial 16S and 12S ribosomal RNA gene sequences". Marine Biology 150 (1): 111–119. doi:10.1007/s00227-006-0335-z. 
  37. ^ Matsumoto, M.; Hayami, I. "Phylogenetic analysis of the family Pectinidae (Bivalvia) based on mitochondrial cytochrome C oxidase subunit". Journal of Molluscan Studies 66 (4): 477–488. doi:10.1093/mollus/66.4.477. 
  38. ^ Pamilo, P.; Nei, M. (1988). "Relationships between gene trees and species trees". Molecular Biology and Evolution 5 (5): 568–583. 
  39. ^ Wu, C.I. (1991). "Inferences of species phylogeny in relation to segregation of ancient polymorphisms.". Genetics 127 (2): 429–435. PMC 1204370. 
  40. ^ Matsumoto, M.; Hayami, I. "Phylogenetic analysis of the family Pectinidae (Bivalvia) based on mitochondrial cytochrome C oxidase subunit". Journal of Molluscan Studies 66 (4): 477–488. doi:10.1093/mollus/66.4.477. 
  41. ^ Waller, T.R., 1998. Origin of the Molluscan Class Bivalvia and a Phylogeny of Major Groups. Pp. 1-45. In: P.A. Johnston & J.W. Haggart (eds), Bivalves: An Eon of Evolution. University of Calgary Press, Calgary. xiv + 461 pp.
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Scallop

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.

A scallop (/ˈskɒləp/ or /ˈskæləp/)[note 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. As members of the subclass pteriomorphia, along with the oysters, ark shells, file shells, shipworms, and saltwater mussels, they are considered a variety of saltwater clam. They are among the only bivalves to be completely free-living and 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, 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.

Anatomy[edit]

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.

Orientation[edit]

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.[1]

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.

Eyes[edit]

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.[2][3] 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.[4] 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.[4] 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.[4]

Digestive system[edit]

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]

Neural map of a giant scallop

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.[1] 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.

Reproduction[edit]

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.

Swimming[edit]

Icelandic scallop Chlamys islandica, equipped with activity electrodes.

The vast majority of adult bivalves are very slow-moving animals. But although some species of scallop can attach themselves to a substrate via their byssus or can even become cemented to their substrate as adults (e.g. Hinnites spp.), most 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 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 swim either forward/ ventrally 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 by ejecting the water out the same way it came in (i.e., ventrally). 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. 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.

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.[5] 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.

Aquaculture[edit]

Main article: Scallop aquaculture

In 2005, China accounted for 80% of the global scallop and pecten catch, according to an FAO study.[6] Outside of China, Russia remained the industry leader.

Sustainability[edit]

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.[7]

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.[8] 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.[9] 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.[10]

Symbolism[edit]

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.[11] Outwardly, the shell can symbolize the protective and nurturing principle, and inwardly, the "life-force slumbering within the Earth",[12] an emblem of the vulva.[13][14]

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'[15]).

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.[16][17]

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).[18] 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.[19]

Heraldry[edit]

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.[20]

Design[edit]

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

[edit]

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.

Notes[edit]

  1. ^ 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.

References[edit]

  1. ^ a b Drew, Gilman Arthur (1906), The Habits Anatomy, and Embryology of the Giant Scallop: (Pecten Tenuicostatus, Mighels), pp. 5–6 
  2. ^ Eyes detect changing movement patterns: queen scallop - Ask Nature - the Biomimicry Design Portal: biomimetics, architecture, biology, innovation inspired by nature, industria...
  3. ^ Land MF and Fernald RD (1992) "The evolution of eyes" Annual review of neuroscience, 15: 1–29.
  4. ^ a b c Land, M F; Fernald, R D (1992). "The Evolution of Eyes". Annual Review of Neuroscience 15: 1–29. doi:10.1146/annurev.ne.15.030192.000245. PMID 1575438. 
  5. ^ 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. 
  6. ^ China catches 1 m tonnes of scallops and pectens in 2005
  7. ^ Scallops | Forest and Bird
  8. ^ http://forums.egullet.org/topic/119187-scallop-roe-do-you-use-it-or-lose-it/
  9. ^ (Rombauer 1964).
  10. ^ AndyTalk: Beyond Lox - Smoked Seafood Hold the Bagels | Phoenix New Times
  11. ^ Salisbury JE (2001) Women in the ancient world, p. 11. ABC-CLIO, ISBN 978-1-57607-092-5.
  12. ^ 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.
  13. ^ Gutzwiller K (1992) "The Nautilus, the Halycon, and Selenaia: Callimachus's Epigram 5 Pf.= 14 G.-P.", Classical Antiquity, 11(2): 175-193.
  14. ^ 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.
  15. ^ Porter D and Prince D (2009) Frommer's Italy 2010, p. 273. Frommer's, ISBN 978-0-470-47069-5.
  16. ^ Slavin S (2003) "Walking as Spiritual Practice: The Pilgrimage to Santiago de Compostela" Body and Society 9(1):18. doi 10.1177/1357034X030093001
  17. ^ 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
  18. ^ Thomas, Isabella. "Pilgrim's Progress". Europe in the UK. European Commission.
  19. ^ 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
  20. ^ "New York State Shell: Bay Scallop". State Symbols USA. Retrieved 2012-05-24. 
  • Barucca M, Olmo E, Schiaparelli S, Canapa A (2004) Molecular phylogeny of the family Pectinidae (Mollusca: Bivalvia)
  • Rombauer, Irma S. and Marion Rombauer Becker (1931 [1964]) The Joy of Cooking, p 369. Indianapolis: Bobbs-Merrill. ISBN 0-452-25665-8.
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