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{{Short description|Species of mollusc, also called St James shell}}
{{Use dmy dates|date=July 2024}}
{{Speciesbox
| image = Pecten maximus Pilgermuschel.jpg
| image_alt =
| image_caption = Two beachworn upper (flat) [[Valve (mollusc)|valves]] of ''Pecten maximus'' from [[Wales]]
| status =
| status_system =
| status_ref = {{citation needed|date=}}
| genus = Pecten
| species = maximus
| authority = ([[Carl Linnaeus|Linnaeus]], [[10th edition of Systema Naturae|1758]])<ref name = WoRMS/>
| synonyms =
*''[[Ostrea]] maxima'' <small>Linnaeus, 1758</small> [[original combination]]
*''[[Pecten (bivalve)|Pecten]] medius'' <small>[[Jean-Baptiste Lamarck|Lamarck]], 1819</small>, [[sensu]] <small>Daniel, 1884</small> misapplication
*''Pecten vulgaris'' <small>[[Emanuel Mendes da Costa|da Costa]], 1778</small><ref>Da Costa, E. M. (1778). Historia naturalis testaceorum Britanniæ, or, the British conchology; containing the descriptions and other particulars of natural history of the shells of Great Britain and Ireland: illustrated with figures. In English and French. - Historia naturalis testaceorum Britanniæ, ou, la conchologie Britannique; contenant les descriptions & autres particularités d'histoire naturelle des coquilles de la Grande Bretagne & de l'Irlande: avec figures en taille douce. En anglois & françois. i-xii, 1-254, i-vii, [1], Pl. I-XVII. London. (Millan, White, Emsley & Robson). , available online at https://www.biodiversitylibrary.org/page/13116783 page(s): 140-143; pl. 9 fig. 3</ref>
*''[[Plicatula]] similis'' <small>([[George Brettingham Sowerby II|G. B. Sowerby II]], 1842)</small><ref>Sowerby, G. B. II. (1842). Monograph of the genus ''Pecten''. In G. B. Sowerby II (ed.), Thesaurus conchyliorum, or monographs of genera of shells. Vol. 1 (2): 45–78, pls 12–20. London, privately published. , available online at https://www.biodiversitylibrary.org/page/43937271 page(s): 46, pl. 16, figs. 116, 117</ref>
*''[[Vola (mollusk)|Vola]] maxima'' <small>(Linnaeus, 1758)</small> [[superseded combination]]
| synonyms_ref =<ref name = WoRMS>MolluscaBase eds. (2024). MolluscaBase. ''Pecten maximus'' (Linnaeus, 1758). Accessed through: World Register of Marine Species at: https://www.marinespecies.org/aphia.php?p=taxdetails&id=140712 on 2024-07-18 </ref>
}}

'''''Pecten maximus''''', [[common names]] the '''great scallop''', '''king scallop''', '''St James shell''' or '''escallop''', is a northeast Atlantic [[species]] of [[scallop]], an edible saltwater [[clam]], a [[marine (ocean)|marine]] [[bivalve]] [[mollusc]] in the family [[Pectinidae]]. This is the type species of the genus. This species may be [[conspecific]] with ''[[Pecten jacobaeus]]'', the [[Shell of Saint James|pilgrim's scallop]], which has a much more restricted distribution.<ref>{{Cite journal | title=Are ''Pecten maximus'' and ''Pecten jacobaeus'' different species?| journal=Journal of the Marine Biological Association of the United Kingdom| volume=79| issue=5| pages=949–952| date=October 1999| last1=Latchford| first1=John W.| last2=Beaumont| first2=Andy R.| last3=Wilding| first3=Craig S.| doi=10.1017/S0025315499001149| bibcode=1999JMBUK..79..949W| s2cid=84757441}}</ref>

==Description==
The shell of ''Pecten maximus'' is quite robust and is characterised by having "ears" of equal size on either side of the apex. The right, or lower, valve is convex and slightly overlaps the flat left, or upper, valve. Larger specimens have a nearly circular outline and the largest may measure 21 cm in length. The "ears" are prominent and are a minimum of half the width of the shell, with the byssal notch situated in the right anterior ear being slight and not serrated. The sculpture of the valves is distinctive and consists of 12 to 17 wide radiating ribs and numerous concentric lines, which clearly show the scallop's growth history, while the "ears" show a few thin ribs, which radiate from the beaks. The radiating ribs reach the margins of the valves and this creates a crenulated form. The left valve is normally reddish-brown whilst the right valve varies from white through cream to shades of pale brown contrasting with pink, red or pale yellow tints; either valve may show zigzag patterns and may also show bands and spots of red, pink or bright yellow.<ref name = FAO>{{cite web |url=http://www.fao.org/fishery/species/3516/en | title = ''Pecten maximus'' (Linnaeus, 1758) | access-date = 1 January 2017 | publisher = [[Food and Agriculture Organization of the United Nations]] Department of Fisheries and Aquaculture}}</ref>

The colour of the body of ''Pecten maximus'' is pink or red with the mantle marbled brown and white. When young they are attached to the substrate by a [[byssus]] but mature animals are capable of swimming by the opening and rapid closing of the valves. The [[Adductor muscle (Bivalvia)|adductor muscle]] which is used to close and open the valves is very large and powerful. The foot is a finger-like organ, which spins the byssal threads, which pass through the byssal notch on the ears. The margin of the mantle has two layers: the inner layer is finely fringed whilst on the outer is lined with long tentacles with two series totalling 30–36 dark blue or green simple eyes or ocelli in two rows at their base.<ref name = MSIP>{{cite web |url=http://species-identification.org/species.php?species_group=mollusca&id=890 | title = Mollusca of the North Sea M.J. de Kluijver, S.S. Ingalsuo & R.H. de Bruyne ''Pecten maximus'' | access-date = 1 January 2017 | publisher = ETI BioInformatics|work = Marine Species Identification Portal}}</ref>

<div align=center>
<gallery mode="packed">
File:Pecten maximus 01.jpg|Right valve
File:Pecten maximus 02.jpg|Left valve
</gallery>
</div align=center>

<div align=center>'''Forma ''maculata'''''
<gallery mode="packed">
File:Pecten maximus 03.jpg|Right valve
File:Pecten maximus 04.jpg|Left valve
</gallery>
</div align=center>

==Distribution==
''Pecten maximus'' occurs in the eastern Atlantic along the European coast from northern [[Norway]], south to the [[Iberian Peninsula]], it has also been reported off West Africa, off the [[Macaronesia]]n Islands. In Great Britain and Ireland it is distributed all round the coast but it is uncommon and localised on the eastern [[North Sea]] coast.<ref name = BIOTIC>{{cite web |url=http://www.marlin.ac.uk/biotic/browse.php?sp=4236 | title = BIOTIC Species Information for Pecten maximus | access-date = 1 January 2016 | publisher = MarLIN (Marine Life Information Network)|work = BIOTIC (Biological Traits Information Catalogue)}}</ref> It prefers offshore waters down to {{convert|100|m|ft fathom|round=5|abbr=off}} depth.<ref name = MSIP/>

==Biology==
[[File:Pecten maximus(02).jpg|thumb|Live individual of ''Pecten maximus'' on the right, next to ''[[Ostrea edulis]]'']]
[[File:Yeux et tentacules d'une coquille Saint-Jacques (Pecten maximus) (Ifremer 00570-68227 - 49129).jpg|thumb|Tentacles and eyes.]]

''Pecten maximus'' frequently creates a slight hollow in the [[substrate (aquatic environment)|substrate]] to lie in by opening and closing for its [[mollusc shell|shell]]s to eject water from the mantle cavity, which raises the shell at an angle to the substrate so that subsequent water jets into the sediment and create a recess.<ref name = BIOTIC/> Once settled, sand, mud, gravel or living organisms coat the upper valve and the margin of the shell, with the tentacles and eyes, is all that is visible.<ref name = FAO/> They are [[filter feeder]]s, which extract particles from the surrounding water via a feeding current, which is drawn by [[cilia]] across the gills, where the food particles are trapped then taken to the mouth in a stream of mucous.<ref name = Beaumont>{{cite report | author1 = A. Beaumont | author2 = T. Gjedrem | date = 2007 | title = Scallops – ''Pecten maximus'' and ''P. jacobaeus'' |url=http://www.imr.no/genimpact/filarkiv/2007/07/scallops.pdf/en | publisher = Genimpact | access-date = 1 January 2017}}</ref>

''Pecten maximus'' swims but this is generally limited to [[escape reaction]]s. The main predators which cause this reaction when detected are the mollusc eating [[starfish]] ''[[Asterias rubens]]'' and ''[[Astropecten irregularis]]'', although starfish which do not feed on molluscs can cause limited jumping or valve-closing reactions. The swimming action is performed by rapidly clapping the valves and expelling jets of water from each side of the hinge so that it moves with the curved edge of the shell at the front. The scallop jumps forwards by gradually relaxing the adductor muscle and then rapidly opening and closing the valves.<ref name = BIOTIC/>

''Pecten maximus'' tends to be more numerous in areas where they are not fully exposed to strong currents. Scallops which live in sheltered habitats grow faster than scallops in areas exposed to wave action, possibly due to the filter feeding apparatus being unable to function because of high concentrations of particulate matter in the water in areas subject to high levels of wave exposure. Another factor that may be significant is that the processes of larval settlement and byssal attachment are rather delicate and would be disturbed in strong currents. Abundance and growth rates are negatively correlated with the amount of mud in the substrate.<ref name = FAO/>

Scallops use larval motility to distribute themselves, as the adult scallops have limited mobility. The distribution of the larvae is affected by factors such as local hydrographic regimes and their survival, and this results in the scallops having an aggregated distribution within their geographic range. This means that the major fishing grounds are normally widely separated and each fishing ground's environmental conditions mean there are marked differences in structures of the populations, although the genetics of scallops are rather uniform across its range.<ref name = BIOTIC/>

The reproductive cycle of ''Pecten maximus'' is extremely variable and the spawning may be influenced by both internal and external factors such as age and temperature respectively but is also influenced by genetic adaptation. Generally, mature scallops spawn over the summer months starting in April or May and lasting to September. They are hermaphroditic and have distinct tongue-shaped gonads which are red or orange in colour for the female gonad and white for the male.<ref name = Beaumont/> It is estimated that a three-year-old scallop releases 15–21 million oocytes per emission. There appear to be two spawnings in many parts of the range, normally there is a partial one in the Spring and a full one in late August, however younger scallops have a single spawning event in the late summer. In some areas this pattern is reversed and the major spawning is in the Spring. After spawning the animals undergo period of recovery of the gonad before they spawn again. Fertilization of the gametes is external and either [[sperm]] or [[oocyte]]s can be released into the water column first.<ref name = BIOTIC/>

Since the larval stage of ''Pecten maximus'' is relatively long, up to a month, the potential for dispersal is quite high, even smaller adults can use the [[byssus]] to drift too. However, in at least some populations, genetic studies show that there is little contribution from more distant populations and that these populations probably sustain themselves.<ref name = BIOTIC/>

In waters around the United Kingdom ''Pecten maximus'' become sexually mature at around 2–3 years old and when they reach 80 to 90 mm in shell length. Where they are not exploited, they may live for more than 20 years and reach shell lengths of more than 200mm.<ref name = York/> Scallops in shallow water grow faster than those in deeper water; the growth halts in winter and starts again in spring, producing concentric growth rings which are used to age the scallops.<ref name = BIOTIC/>

===Genomics===
A draft [[genome]] is presented by Kenny et al. 2020.<ref name="Potts-et-al-2021">{{cite journal | last1=Potts | first1=Robert W. A. | last2=Gutierrez | first2=Alejandro P. | last3=Penaloza | first3=Carolina S. | last4=Regan | first4=Tim | last5=Bean | first5=Tim P. | last6=Houston | first6=Ross D. | title=Potential of genomic technologies to improve disease resistance in molluscan aquaculture | journal=[[Philosophical Transactions of the Royal Society B]] | publisher=The [[Royal Society]] | volume=376 | issue=1825 | date=5 April 2021 | issn=0962-8436 | doi=10.1098/rstb.2020.0168|pmc=8059958 | page=20200168| pmid=33813884 }}</ref><ref name="Yang-et-al-2020">{{cite journal | last1=Yang | first1=Zhihui | last2=Zhang | first2=Lingling | last3=Hu | first3=Jingjie | last4=Wang | first4=Jing | last5=Bao | first5=Zhenmin | last6=Wang | first6=Shi | title=The evo-devo of molluscs: Insights from a genomic perspective | journal=[[Evolution & Development]] | publisher=[[Wiley Periodicals|Wiley]] | volume=22 | issue=6 | date=14 April 2020 | issn=1520-541X | doi=10.1111/ede.12336 | pages=409–424| pmid=32291964 | s2cid=215774459 }}</ref> Their assembly is 918Mb, and they estimate a [[genome size]] of 1,150Mb, 1.7% [[heterozygosity]], with 27.0% being repeats, in total coding 67,741 genes.<ref name="Yang-et-al-2020" /> Recent ({{as of|2021|lc=yes}}) improvements in [[read length]] helped Kenny to resolve questions of [[copy number variation]] in ''P. maximus'' which were previously indecipherable.<ref name="Potts-et-al-2021" />

==Predators and diseases==
As well as the [[starfish]] species ''[[Common starfish|Asterias rubens]]'' and ''[[Astropecten irregularis]]'', major predators of ''Pecten maximus'' are crabs such as ''[[Cancer pagurus]]'', ''[[Carcinus maenas]]'', ''[[Liocarcinus depurator]]'' and ''[[Necora puber]]'', which will prey on the scallops as they grow.<ref name = Lake>{{cite journal | author1 = N. C. H. Lake | author2 = M. B. Jones | author3 = J. D. Paul | year = 1987 | title = Crab predation on scallop (''Pecten maximus'') and its implication for scallop cultivation | journal = Journal of the Marine Biological Association of the United Kingdom | volume = 67 | issue = 1 | pages = 55–64 | doi=10.1017/s0025315400026357| bibcode = 1987JMBUK..67...55L | s2cid = 84831172 }}</ref> The anemone ''[[Anthopleura ballii]]'' was found preying on young specimens of ''P.maximus'' in south-western Ireland.<ref name = Minchin>{{cite journal | author1 = Dan Minchin | year = 1982 | title = Predation on young ''Pecten maximus'' (L.) (Bivalvia), by the anemone ''Anthopleura ballii'' (Cocks) | journal = Journal of Molluscan Studies | volume = 49 | issue = 3 | pages = 228–231 | doi=10.1093/oxfordjournals.mollus.a065717}}</ref>

The larvae of ''Pecten maximus'' are attacked by the bacterium ''[[Vibrio pectenicida]]'', which was described in 1998 as a new species after incidents of mortality among cultured scallops in France in the early 1990s.<ref name = IJSB>{{cite journal | author1 = C Lambert | author2 = JL Nicolas | author3 = V Cilia |author4 = S Corre | year = 1998 | title = ''Vibrio pectenicida'' sp. nov., a pathogen of scallop (''Pecten maximus'') larvae | journal = International Journal of Systematic Bacteriology | volume = 48 | issue = 2 | pages = 481–487 | doi=10.1099/00207713-48-2-481 | pmid=9731288|url=https://hal.archives-ouvertes.fr/hal-00447706/document | doi-access = free }}</ref> Other strains of pathogenic bacteria were detected in Norway following mass mortality of larvae in culture.<ref name = Torkildsen>{{cite journal | author1 = Lise Thorkildsen | author2 = Christophe Lambert | author3 = Are Nylund | author4 = Thorolf Magnesen | author5 = Øivind Bergh | year = 2005 | title = Bacteria associated with early life stages of the great scallop, ''Pecten maximus'': impact on larval survival | journal = Aquaculture International | volume = 13| issue = 6 | pages = 575–592 | doi=10.1007/s10499-005-9002-5| bibcode = 2005AqInt..13..575T | s2cid = 20819269 |url=https://hal.archives-ouvertes.fr/hal-00590935/file/Torkildsen_et_al_2005_Aquacult_Int_13_575-592_.pdf }}</ref>

==Fisheries and aquaculture==
[[File:Great atlantic scallop, capture production, thousand tonnes, 1950-2022.svg|thumb|Global capture production of Great Atlantic scallop (''Pecten maximus'') in thousand tonnes from 1950 to 2022, as reported by the [[Food and Agriculture Organization|FAO]]<ref>{{Cite web |title=Fisheries and Aquaculture - Global Production |url=https://www.fao.org/fishery/en/collection/global_production?lang=en |access-date=2024-05-06 |website=Food and Agriculture Organization of the United Nations (FAO)}}</ref>]]
In 1999 the total catch reported by the United Nations Food and Agriculture Organisation was 35,411 tonnes with the two biggest catches being reported from the [[United Kingdom]] and [[France]] which landed 19,108 tonnes and 12,745 tonnes respectively.<ref name = FAO/> It is believed that some natural stocks are showing indications of over exploitation resulting in strict enforcement of fisheries legislation and by the development of stock enhancement practices.<ref name = Briggs>{{cite journal | author = R.P. Briggs | year = 2000 | title = The great scallop: an endangered species. | journal = Biologist | volume = 47 | issue = 5 | pages = 260–264| pmid = 11153135 }}</ref> Great scallops are fished for using Newhaven scallop dredges, and less than 5% is gathered by hand by [[Scuba diving|divers]]. In total the scallop fisheries for ''P. maximus'' and for the Queen scallop ''[[Aequipecten opercularis]]'' are one of the top five fisheries by value in United Kingdom waters. However, the use of towed great to harvest scallops causes damage to the wider ecosystem.<ref name = York>{{cite report | author1= Bryce D. Beukers-Stewart | author2 = Joanne S. Beukers-Stewart |date= 2009 |title= Principles for the Management of Inshore Scallop Fisheries around the UK |url=http://www.arrancoast.com/website_pdf/beukers_stewart_scallop_proposed_management_inuk.pdf| publisher= [[University of York]] |access-date= 1 January 2016}}</ref>

''Pecten maximus'' can be cultivated in [[aquaculture]] and this is reasonably advanced in France<ref name = ALR>{{cite journal | author1 = Nicole Devauchelle | author2 = Christian Mingant | year = 1991 | title = Review of the reproductive physiology of the scallop, ''Pecten maximus'', applicable to intensive aquaculture |url=http://archimer.ifremer.fr/doc/00038/14890/12216.pdf | journal = Aquatic Living Resources | volume = 2 | issue = 1 | pages = 41–51| doi = 10.1051/alr:1991004 | bibcode = 1991AqLR....4...41D }}</ref> and Norway.<ref name = AI>{{cite journal | author1 = Øivind Bergh | author2 = Øivind Strand | year = 2001 | title = Great scallop, ''Pecten maximus'', research and culture strategies in Norway: a review | journal = Aquaculture International | volume = 9 | issue = 4 |pages = 305–317 | doi=10.1023/A:1020452715518| s2cid = 45170157 }}</ref> Spain, France, Ireland, the United Kingdom and Norway have been involved in the aquaculture of scallops; production peaked in 1998 when 512 tonnes were landed but production later decreased, with only 213 tonnes landed in 2004, having an estimated value of €852 000, equivalent to €4 per kilogramme.<ref name = Beaumont/>

''Pecten maximus'' has been found to contain [[domoic acid]], a toxin that can cause [[Amnesic Shellfish Poisoning]]. The risk associated with scallop consumption is regarded as a significant threat to both public health and the shellfish industry.<ref name = BIOTIC/>

==Cultural significance==
The oil company [[Shell plc]] derives its highly recognizable logo from this species.<ref name = Ecomare>{{cite web |url=http://www.ecomare.nl/en/encyclopedia/organisms/animals/invertebrates/molluscs/bivalves-group/great-scallop/ | title = Great scallop | access-date = 1 January 2016 | publisher = Ecomare | url-status=dead | archive-date = 1 January 2017 | archive-url=https://web.archive.org/web/20170101232744/http://www.ecomare.nl/en/encyclopedia/organisms/animals/invertebrates/molluscs/bivalves-group/great-scallop/ | quote = Lat: Pecten Maximus Eng: St James scallop }}</ref>

Pilgrims travelling to the town of [[Santiago de Compostella]] in [[Galicia (Spain)|Galicia]] took the shells of scallop with them, in honor of Saint James. This gave rise to the alternative name St James shell.<ref name = Ecomare/>

[[Michel Callon]], a sociologist, used a case study of scallop fishing in [[Saint-Brieuc|St Brieuc Bay]] in France to illustrate how the sociology of translation can be applied to understand the dynamics of science and technology. This study then became a seminal work of [[actor-network theory]] (ANT).<ref>{{Cite journal |last=Callon |first=Michel |date=May 1984 |title=Some Elements of a Sociology of Translation: Domestication of the Scallops and the Fishermen of St Brieuc Bay |url=http://journals.sagepub.com/doi/10.1111/j.1467-954X.1984.tb00113.x |journal=The Sociological Review |language=en |volume=32 |issue=1_suppl |pages=196–233 |doi=10.1111/j.1467-954X.1984.tb00113.x |s2cid=15055718 |issn=0038-0261|url-access=subscription }}</ref>

==See also==
* [[Scallop#Symbolism of the shell|Symbolism of scallop shells]]

==References==
{{Reflist}}

==External links==
{{Commons category|Pecten maximus}}
* [https://web.archive.org/web/20071222172302/http://www.seawater.no/fauna/Blotdyr/images/DSC09090.jpg A live individual, upper shell covered in sediment]
* [http://www.marlin.ac.uk/species/pectenmaximus.htm MarLIN info]

{{commercial molluscs}}
{{Edible molluscs}}
{{Taxonbar|from=Q1249634}}
{{Authority control}}

[[Category:Pectinidae]]
[[Category:Molluscs of the Atlantic Ocean]]
[[Category:Molluscs described in 1758]]
[[Category:Taxa named by Carl Linnaeus]]

Pecten maximus - Revision history

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