{{Short description|Species of gastropod}} {{Speciesbox | name = | image = Polycera quadrilineata (Müeller O.F., 1776).jpg | image_caption = ''Polycera quadrilineata'' from France | taxon = Polycera quadrilineata | authority = (O. F. Müller, 1776)<ref name=orig>Müller, Otto Frederik. (1776) ''Zoologiae Danicae. Prodromus seu animalium Daniae et Norvegiae ingenarum characteres, nomina, et synonyma imprimis popularium'', xxxii + 282 pp.</ref> | synonyms_ref = <ref>MolluscaBase (2019). MolluscaBase. [http://www.marinespecies.org/aphia.php?p=taxdetails&id=140838 ''Polycera quadrilineata'' (O. F. Müller, 1776).] Accessed through: World Register of Marine Species on 2019-10-11.</ref> | synonyms = * ''Doris cornuta'' Rathke, 1806<ref>Rathke J., 1806. [in] Müller O. F., Zoologia Danica ed. III</ref> * ''Doris flava'' Montagu, 1804<ref>Montagu G., 1804. ''Description of several marine animals found on the South coast of Devonshire''; Transactions of the Linnean Society of London 7: 61-85</ref> * ''Doris marplatensis'' Franceschi, 1928 * ''Doris quadrilineata'' O.F. Müller, 1776 * ''Polycera lineatus'' Risso, 1826<ref>Risso A., 1826-1827. ''Histoire naturelle des principales productions de l'Europe Méridionale et particulièrement de celles des environs de Nice et des Alpes Maritimes''; Paris, Levrault</ref> * ''Polycera mediterranea'' Bergh, 1879 * ''Polycera nigrolineata'' Dautzenberg & Durouchoux, 1913<ref>Dautzenberg P. & Durouchoux P., 1913-1914: ''Les mollusques de la baie de Saint-Malo'': Feuille des Jeunes Naturalistes 43-44 (Suppl.): 1-64, pl. 1-4</ref> * ''Polycera nigropicta'' Ihering, 1885<ref>Ihering H. von, 1886. ''Beiträge zur kenntnis der Nudibranchien des Mittelmeeres. Part 2''; Malakozoologische Blätter N.F. 8: 12-48</ref> * ''Polycera ornata'' d'Orbigny, 1837<ref>Orbigny A. D. d', 1837. ''Mémoire sur des espèces et sur des genres nouveaux de l'ordre des nudibranches observés sur les côtes de France''; Revue et Magasin de Zoologie 7 (5): 1-16</ref> * ''Polycera salamandra'' Labbé, 1931<ref>Labbé A., 1931. ''Les Polycerades de la station du Croisic et description sommaire d'une espèce nouvelle : Polycera salamandra n. sp.''; Bulletin de la Société Zoologique de France 56 : 19-24.</ref> * ''Polycera typica'' W. Thompson, 1840<ref>Thompson W., 1840. ''Contributions towards a knowledge of the Mollusca Nudibranchia and Mollusca Tunicata of Ireland, with descriptions of some apparently new species of Invertebrata''; Annals and Magazine of Natural History 5 (29): 84-102</ref> * ''Polycera varians'' M. Sars, 1840 * ''Thecacera capitata'' Alder & Hancock, 1854<ref>Alder J. & Hancock A. (1854). Notice of some new species of British Nudibranchiata. Annals and Magazine of Natural History. ser. 2, 14: 102-105.</ref> }}
''Polycera quadrilineata'', is a sea slug, a species of dorid nudibranch. It is a marine gastropod mollusc in the family Polyceridae. The specific epithet ''quadrilineata'' means four-lined and refers to the four longitudinal black lines present on the original specimen. This species is sometimes called the fourline nudibranch. In 2020 a integrative molecular and morphological study showed that ''P. quadrilineata'' was a complex of two species in the NE Atlantic and one of these species was given the new name ''Polycera norvegica''.
==Distribution== This nudibranch was described originally from Norway.<ref name=orig/> In the NE Atlantic it is a common species in shallow water.<ref name=pm>Picton, B.E. & Morrow, C.C., 2010. [http://www.habitas.org.uk/marinelife/species.asp?item=W13630 ''Polycera quadrilineata''] <nowiki>[In]</nowiki> Encyclopedia of Marine Life of Britain and Ireland.</ref> It is distributed from Greenland to Norway and south along the European coasts into the Mediterranean Sea. It is found from the intertidal zone to 160 m.
It has also been reported off the South African coast from the Atlantic coast of the Cape Peninsula to Algoa Bay.<ref name=gosliner1987>Gosliner, T.M. 1987. ''Nudibranchs of Southern Africa'' {{ISBN|0-930118-13-8}}</ref> The South African animals differ in having six instead of four papillae projecting from the frontal margin of the head, plus details of the coloration. These animals have been shown to be an undescribed species by studies in 2014 and 2020.<ref>Palomar, G.; Pola, M.; Garcia-Vazquez, E. (2014). First molecular phylogeny of the subfamily Polycerinae (Mollusca, Nudibranchia, Polyceridae). Helgoland Marine Research. 68(1): 143-153.</ref><ref>{{cite journal |last1=Sørensen |first1=Cecilie Gotaas |last2=Rauch |first2=Cessa |last3=Pola |first3=Marta |last4=Malaquias |first4=Manuel António E. |name-list-style=amp |title=Integrative taxonomy reveals a cryptic species of the nudibranch genus ''Polycera'' (Polyceridae) in European waters |journal=Journal of the Marine Biological Association of the United Kingdom |date=2020 |volume=100 |issue=5 |pages=733–752 |doi=10.1017/s0025315420000612|doi-access=free |bibcode=2020JMBUK.100..733S }}</ref> thumb|left|The nudibranch ''Polycera quadrilineata'', Gulen Dive Resort, Norway.
==Description== ''Polycera quadrilineata'' is a smooth-bodied, variably coloured nudibranch. The ground colour is white or grey and there are usually black, yellow or orange stripes longitudinally along the notum, though these can be absent. The head has four or occasionally six yellow projections. The gills and rhinophores are translucent white, tipped with yellow. There are two processes at the sides of the gill cluster with glandular, orange or yellow pigmented tips matching the general orange or yellow colour of the body pigmentation.<ref>Thompson, T.E. 1988. ''Molluscs: Benthic Opisthobranchs'' Linnean Society of London. {{ISBN|90 04 08439 8}}</ref>
In the South African animals the gills and rhinophores are black, and may be spotted with yellow. Alongside the gills is a pair of yellow-tipped projections. The animal may reach 20mm in total length. It is distinguished from the crowned nudibranch in having raised yellow spots on the mid-dorsal region.<ref name=gosliner1987/>
==Ecology== ''Polycera quadrilineata'' feeds mostly on the bryozoans ''Membranipora membranacea'' and ''Electra pilosa''.<ref name=pm/>
==References== {{Reflist}}
==External links== {{Commons category}} * {{SealifePhotos|140838}}
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Category:Polyceridae Category:Molluscs of the Atlantic Ocean Category:Gastropods described in 1776 Category:Taxa named by Otto Friedrich Müller