Barnacle

The word "barnacle" is attested in the early 13th century as Middle English "bernekke" or "bernake", close to Old French "bernaque" and medieval Latin bernacae or berneka, denoting the barnacle goose.{{cite book |last=Müller |first=F. Max |author-link=Max Müller |year=1871 |title=Lectures on the Science of Language |location=London |publisher=Longmans, Green |volume=2 |pages=583–604}} Because the full life cycles of both barnacles and geese were unknown at the time, (geese spend their breeding seasons in the Arctic) a folktale emerged that geese hatched from barnacles. It was not applied strictly to the arthropod until the 1580s. The ultimate meaning of the word is unknown.{{cite web |title=barnacle (n.) |website=Online Etymology Dictionary |url=https://www.etymonline.com/word/barnacle |accessdate=19 February 2024}}{{cite encyclopedia |chapter=Barnacle |dictionary=Oxford English Dictionary |edition=2nd |year=1989}}

The name {{lang|la|Cirripedia}} comes from the Latin words cirritus "curly" from cirrus "curl"{{cite encyclopedia |url=http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0059:entry=cirrus |title=cirrus |last1=Lewis |first1=Charlton T. |last2=Short |first2=Charles |dictionary=A Latin Dictionary |edition=|publisher=Perseus Digital Library |date=1879 }} and pedis from pes "foot".{{cite encyclopedia |url=http://www.perseus.tufts.edu/hopper/text?doc=Perseus:text:1999.04.0059:entry=pes |title=lavo |last1=Lewis |first1=Charlton T. |last2=Short |first2=Charles |dictionary=A Latin Dictionary |publisher=Perseus Digital Library |date=1879 }} The two words together mean "curly-footed", alluding to the curved legs used in filter-feeding.{{cite book |title=Concise Oxford English Dictionary |edition=10th |publisher=Oxford University Press |page=260 |date=2002 |isbn=0-19-860572-2}}

File:Anim1032 - Flickr - NOAA Photo Library.jpgs on a humpback whale ]]

Most barnacles are encrusters, attaching themselves to a hard substrate such as a rock, the shell of a mollusc, or a ship; or to an animal such as a whale (whale barnacles). The most common form, acorn barnacles, are sessile, growing their shells directly onto the substrate, whereas goose barnacles attach themselves by means of a stalk.{{cite journal |last1=Doyle |first1=Peter |last2=Mather |first2=Anne E. |last3=Bennett |first3=Matthew R. |last4=Bussell |first4=M. Andrew |title=Miocene barnacle assemblages from southern Spain and their palaeoenvironmental significance |journal=Lethaia |volume=29 |issue=3 |date=1996 |issn=0024-1164 |doi=10.1111/j.1502-3931.1996.tb01659.x |pages=267–274|bibcode=1996Letha..29..267D }}

File:Barnacles Sessile anatomy.svg

Barnacles have a carapace made of six hard calcareous plates, with a lid or operculum made of four more plates. Inside the carapace, the animal lies on its stomach, projecting its limbs downwards. Segmentation is usually indistinct; the body is more or less evenly divided between the head and thorax, with little or no abdomen. Adult barnacles have few appendages on their heads, with only a single, vestigial pair of antennae attached to the cement gland. The six pairs of thoracic limbs are called cirri; these are feathery and very long. The cirri extend to filter food, such as plankton, from the water and move it towards the mouth.

Acorn barnacles are attached to the substratum by cement glands that form the base of the first pair of antennae; in effect, the animal is fixed upside down by means of its forehead. In some barnacles, the cement glands are fixed to a long, muscular stalk, but in most they are part of a flat membrane or calcified plate. These glands secrete a type of natural quick cement made of complex protein bonds (polyproteins) and other trace components like calcium.{{cite journal |last1=Xu |first1=Zhenzhen |last2=Liu |first2=Zhongcheng |last3=Zhang |first3=Chao |last4=Xu |first4=Donggang |title=Advance in barnacle cement with high underwater adhesion |url=https://onlinelibrary.wiley.com/doi/full/10.1002/app.52894 |date=October 2022 |journal=Journal of Applied Polymer Science |volume=139 |issue=37 |pages=1–12 |doi=10.1002/app.52894 |s2cid=251335952 |url-access=subscription }}{{rp|2–3}} This natural cement can withstand a pulling strength of {{convert|5000|lb/in2|kPa|sigfig=1|abbr=on}} and a sticking strength of {{convert|22-60|lb/in2|kPa|sigfig=1|abbr=on}}.{{cite web |url=https://oceanservice.noaa.gov/facts/barnacles.html |title=What are barnacles? |date=26 February 2021 |website=Ocean Facts |publisher=National Ocean Service, National Oceanic and Atmospheric Administration |access-date=18 June 2022}}

Barnacles have no true heart, although a sinus close to the esophagus performs a similar function, with blood being pumped through it by a series of muscles.{{Cite web |title=Barnacles |website=Encyclopedia of Life |url=https://eol.org/pages/45500159/articles |access-date=2023-06-07 }} The blood vascular system is minimal.{{cite book |last=Burnett |year=1987 |title=The cirripede circulatory system and its evolution}} In A. J. Southward (ed.), 1987. Similarly, they have no gills, absorbing oxygen from the water through the cirri and the surface of the body.{{cite web |title=Acorn barnacle |url=https://www.montereybayaquarium.org/animals/animals-a-to-z/acorn-barnacle |publisher=Monterey Bay Aquarium |access-date=18 February 2024}} The excretory organs of barnacles are maxillary glands.{{cite journal |last1=White |first1=K. N. |last2=Walker |first2=G. |title=The barnacle excretory organ |journal=Journal of the Marine Biological Association of the United Kingdom |volume=61 |issue=2 |date=1981 |doi=10.1017/S0025315400047123 |pages=529–547 |bibcode=1981JMBUK..61..529W |s2cid=83903175 }}

The main sense of barnacles appears to be touch, with the hairs on the limbs being especially sensitive. The adult has three photoreceptors (ocelli), one median and two lateral. These record the stimulus for the barnacle shadow reflex, where a sudden decrease in light causes cessation of the fishing rhythm and closing of the opercular plates.{{cite journal |last1=Gwilliam |first1=G. F. |last2=Millecchia |first2=R. J. |date=January 1975 |title=Barnacle photoreceptors: Their physiology and role in the control of behavior |journal=Progress in Neurobiology |volume=4 |pages=211–239 |doi=10.1016/0301-0082(75)90002-7|s2cid=53164671 }} The photoreceptors are likely only capable of sensing the difference between light and dark.{{cite book |last=Barnes |first=Robert D. |year=1982 |title=Invertebrate Zoology |publisher=Holt-Saunders International |pages= 694–707 |isbn= 978-0-03-056747-6}} This eye is derived from the primary naupliar eye.{{cite journal |last1=Lacalli |first1=Thurston C. |title=Serial EM analysis of a copepod larval nervous system: Naupliar eye, optic circuitry, and prospects for full CNS reconstruction |journal=Arthropod Structure & Development |date=September 2009 |volume=38 |issue=5 |pages=361–375 |doi=10.1016/j.asd.2009.04.002 |pmid=19376268 |bibcode=2009ArtSD..38..361L }}

Barnacles pass through two distinct larval stages, the nauplius and the cyprid, before developing into a mature adult.

A fertilised egg hatches into a nauplius: a one-eyed larva comprising a head and a telson with three pairs of limbs, lacking a thorax or abdomen. This undergoes six moults, passing through five instars, before transforming into the cyprid stage. Nauplii are typically initially brooded by the parent, and released after the first moult as larvae that swim freely using setae.{{cite book |last=Newman |first=William A. |chapter=Cirripedia |editor1=Sol Felty Light |editor2=James T. Carlton |pages=475–484 |title=The Light and Smith Manual: Intertidal Invertebrates from Central California to Oregon |edition=4th |publisher=University of California Press |year=2007 |isbn=978-0-520-23939-5}}{{cite book |title=Invertebrate Zoology |edition=7th |last1=Ruppert |first1=Edward E. |last2=Fox |first2=Richard S. |last3=Barnes |first3=Robert D. |year=2004 |publisher=Cengage Learning |isbn=978-81-315-0104-7 |page=683}} All but the first instars are filter feeders.{{cite book |last1=Poore |first1=Gary C. B. |last2=Syme |first2=Anna |year=2009 |title=Barnacles |publisher=Museums Victoria |isbn=9780980381351 |page=11}}

File:Elminius modestus nauplius.jpg|Nauplius larva of Elminius modestus

File:Cirripedia nauplius.png|Nauplius with fronto-lateral horns{{cite journal |last1=Pérez-Losada |first1=Marcos |last2=Høeg |first2=Jens T. |last3=Crandall |first3=Keith A. |author-link3=Keith A. Crandall |title=Remarkable convergent evolution in specialized parasitic Thecostraca (Crustacea) |journal=BMC Biology |date=17 April 2009 |volume=7 |issue=1 |pages=15 |doi=10.1186/1741-7007-7-15 |pmid=19374762 |pmc=2678073 |doi-access=free }}

{{anchor|Cyprid}}

The cypris larva is the second and final larval stage before adulthood. In Rhizocephala and Thoracica an abdomen is absent in this stage, but the y-cyprids (post-naupliar instar) has three distinct abdominal segments.{{cite journal |last1=Hoeg |first1=Jens |last2=Pérez-Losada |first2=Marcos |last3=Glenner |first3=Henrik |last4=Kolbasov |first4=Gregory |last5=Crandall |first5=Keith |title=Evolution of Morphology, Ontogeny and Life Cycles within the Crustacea Thecostraca |journal=Arthropod Systematics & Phylogeny |date=25 August 2009 |volume=67 |issue=2 |pages=199–217 |doi=10.3897/asp.67.e31697 |doi-access=free}} It is not a feeding stage; its role is to find a suitable place to settle, since the adults are sessile. The cyprid stage lasts from days to weeks. It explores potential surfaces with modified antennules; once it has found a suitable spot, it attaches head-first using its antennules and a secreted glycoproteinous cement. Larvae assess surfaces based upon their surface texture, chemistry, relative wettability, color, and the presence or absence and composition of a surface biofilm; swarming species are more likely to attach near other barnacles.{{cite book |last=Anderson |first=Donald Thomas |year=1994 |title=Barnacles: Structure, Function, Development and Evolution |publisher=Springer |isbn=978-0-412-44420-3 |chapter=Larval development and metamorphosis |pages=197–246 |chapter-url=https://books.google.com/books?id=2MDH9IRDkdkC&pg=PA219}} As the larva exhausts its energy reserves, it becomes less selective in the sites it selects. It cements itself permanently to the substrate with another proteinaceous compound, and then undergoes metamorphosis into a juvenile barnacle.

Balanus improvisus, cypris (rotated).jpg|Cypris larva of Amphibalanus improvisus

File:Barnacles Cypris anatomy diagram vecorized.svg|Anatomy of cypris larva

Typical acorn barnacles develop six hard calcareous plates to surround and protect their bodies. For the rest of their lives, they are cemented to the substrate, using their feathery legs (cirri) to capture plankton. Once metamorphosis is over and they have reached their adult form, barnacles continue to grow by adding new material to their heavily calcified plates. These plates are not moulted; however, like all ecdysozoans, the barnacle moults its cuticle.{{cite book |author=E. Bourget |year=1987 |title=Barnacle shells: composition, structure, and growth |pages=267–285}} In A. J. Southward (ed.), 1987.

File:Balanus reproduction.svg

Most barnacles are hermaphroditic, producing both eggs and sperms. A few species have separate sexes, or have both males and hermaphrodites. The ovaries are located in the base or stalk, and may extend into the mantle, while the testes are towards the back of the head, often extending into the thorax. Typically, recently moulted hermaphroditic individuals are receptive as females. Self-fertilization, although theoretically possible, has been experimentally shown to be rare in barnacles.{{cite web |url=http://www.museum.vic.gov.au/crust/barnbiol.html |publisher=Museum Victoria |title=Biology of Barnacles |year=1996 |access-date=April 20, 2012 |archive-url=https://web.archive.org/web/20070217160059/http://www.museum.vic.gov.au/crust/barnbiol.html |archive-date=February 17, 2007}}{{cite book |last=Charnov |first=E. L. |year=1987 |title=Sexuality and hermaphroditism in barnacles: A natural selection approach |pages=89–104}} In A. J. Southward (ed.), 1987.

The sessile lifestyle of acorn barnacles makes sexual reproduction difficult, as they cannot leave their shells to mate. To facilitate genetic transfer between isolated individuals, barnacles have developed extraordinarily long penises⁠. Barnacles possess the largest penis-to-body size ratio of any known animal, up to eight times their body length, though on exposed coasts the penis is shorter and thicker.{{cite magazine |last=Callaway |first=Ewen |title=Penis length isn't everything … for barnacle males |date=17 April 2009 |url=https://www.newscientist.com/article/dn16971-penis-length-isnt-everything-for-barnacle-males/ |magazine=New Scientist |access-date=19 February 2024}} The mating of acorn barnacles is described as pseudocopulation.{{Cite journal |last1=Bishop |first1=J. D. D. |last2=Pemberton |first2=A. J. |date=2005 |title=The third way: spermcast mating in sessile marine invertebrates |journal=Integrative and Comparative Biology |volume=46 |issue=4 |pages=398–406 |doi=10.1093/icb/icj037 |pmid=21672752 |doi-access=free}}

The goose barnacle Pollicipes polymerus can alternatively reproduce by spermcasting, in which the male barnacle releases his sperm into the water, to be taken up by females. Isolated individuals always made use of spermcasting and sperm capture, as did a quarter of individuals with a close neighbour. This 2013 discovery overturned the long-held belief that barnacles were limited to pseudocopulation or hermaphroditism.{{cite journal |last1=Barazandeh |first1=Marjan |last2=Davis |first2=Corey S. |last3=Neufeld |first3=Christopher J. |last4=Coltman |first4=David W. |last5=Palmer |first5=A. Richard |title=Something Darwin didn't know about barnacles: spermcast mating in a common stalked species |journal=Proceedings of the Royal Society B: Biological Sciences |volume=280 |issue=1754 |date=2013-03-07 |pmid=23325777 |pmc=3574338 |doi=10.1098/rspb.2012.2919 |page=20122919}}

Rhizocephalan barnacles had been considered hermaphroditic, but their males inject themselves into females' bodies, degrading to little more than sperm-producing cells.{{cite book |last=Dale |first=Brian |title=Mechanism of Fertilization: Plants to Humans |publisher=Springer |year=2013 |isbn=978-3-642-83965-8 |page=[https://books.google.com/books?id=fVjxCAAAQBAJ&pg=PA702 702]}}

Most barnacles are filter feeders. From within their shell, they repeatedly reach into the water column with their cirri. These feathery appendages beat rhythmically to draw plankton and detritus into the shell for consumption.{{cite book |last1=Riisgård |first1=Hans Ulrik |editor1=Thiel, Martin |editor2=Watling, Les |chapter=Filter-feeding mechanisms in crustaceans |title=Life styles and feeding biology. The natural history of the Crustacea |volume=2 |year=2015 |publisher=Oxford University Press |url=https://www.researchgate.net/publication/289520648 |pages=418–463}}

File:Giant Acorn Barnacle, Embarcadero, Morro Bay, CA, US imported from iNaturalist photo 149595197.jpg|Balanus nubilus with cirri extended

File:Entenmuscheln.jpg|Goose barnacles, with their cirri extended for feeding

File:Scalpellid barnacle feeding.jpg|A scalpellid barnacle feeding

File:Semibalanus balanoides upernavik 2007-07-05.ogv|Semibalanus balanoides filter-feeding by projecting and retracting their cirri

Although they have been found at water depths to {{convert|600|m|ft|-2|abbr=on}}, most barnacles inhabit shallow waters, with 75% of species living in water depths less than {{convert|100|m|ft|-2|abbr=on}}, and 25% inhabiting the intertidal zone. Within the intertidal zone, different species of barnacles live in very tightly constrained locations, allowing the exact height of an assemblage above or below sea level to be precisely determined.

Since the intertidal zone periodically desiccates, barnacles are well adapted against water loss. Their calcite shells are impermeable, and they can close their apertures with movable plates when not feeding.{{cite journal |last=Buckeridge |first=John S. |title=Opportunism and the resilience of barnacles (Cirripedia: Thoracica) to environmental change |journal=Integrative Zoology |volume=7 |issue=2 |date=2012 |issn=1749-4877 |doi=10.1111/j.1749-4877.2012.00286.x |pages=137–146|pmid=22691197 }} Their hard shells are assumed by zoologists to have evolved as an anti-predator adaptation.{{cite journal |last1=Zimmer |first1=Richard K. |last2=Ferrier |first2=Graham A. |last3=Zimmer |first3=Cheryl Ann |title=Chemosensory Exploitation and Predator-Prey Arms Races |journal=Frontiers in Ecology and Evolution |volume=9 |date=2021-11-12 |issn=2296-701X |doi=10.3389/fevo.2021.752327 |doi-access=free |page=}}

One group of stalked barnacles has adapted to a rafting lifestyle, drifting around close to the water's surface. They colonize every floating object, such as driftwood, and like some non-stalked barnacles attach themselves to marine animals. The species most specialized for this lifestyle is Dosima fascicularis, which secretes a gas-filled cement that makes it float at the surface.{{Cite journal |last1=Zheden |first1=Vanessa |last2=Kovalev |first2=Alexander |last3=Gorb |first3=Stanislav N. |last4=Klepal |first4=Waltraud |date=2015-02-06 |title=Characterization of cement float buoyancy in the stalked barnacle Dosima fascicularis (Crustacea, Cirripedia) |journal=Interface Focus |volume=5 |issue=1 |pages=20140060 |doi=10.1098/rsfs.2014.0060 |pmc=4275874 |pmid=25657839}}

File:Sacculina carcini.jpg (highlighted) parasitising the crab Liocarcinus holsatus. ]]

Other members of the class have an entirely different mode of life. Barnacles of the superorder Rhizocephala, including the genus Sacculina, are parasitic castrators of other arthropods, including crabs. The anatomy of these parasitic barnacles is greatly reduced compared to their free-living relatives. They have no carapace or limbs, having only unsegmented sac-like bodies. They feed by extending thread-like rhizomes of living cells into their hosts' bodies from their points of attachment.{{cite web |url=http://www.marlin.ac.uk/species/detail/2233 |title=Crab hacker barnacle (Sacculina carcini) |last=Hosie |first=A. M. |year=2008 |publisher=MarLIN |access-date=14 January 2018 |url-status=live |archive-url=https://web.archive.org/web/20180115184524/http://www.marlin.ac.uk/species/detail/2233 |archive-date=15 January 2018 }}

Goose barnacles of the genus Anelasma (in the order Pollicipedomorpha) are specialized parasites of certain shark species. Their cirri are no longer used to filter-feed. Instead, these barnacles get their nutrients directly from the host through a root-like body part embedded in the shark's flesh.{{cite journal |last=Rees |first=David John |date=16 June 2014 |title=On the Origin of a Novel Parasitic-Feeding Mode within Suspension-Feeding Barnacles |journal=Current Biology |volume=24 |issue=12 |pages=1429-1434 |doi=10.1016/j.cub.2014.05.030 |doi-access=free}}

File:CornishBarnacles.JPGs compete for space in the intertidal zone]]

Barnacles are displaced by limpets and mussels, which compete for space. They employ two strategies to overwhelm their competitors: "swamping", and fast growth. In the swamping strategy, vast numbers of barnacles settle in the same place at once, covering a large patch of substrate, allowing at least some to survive in the balance of probabilities. Fast growth allows the suspension feeders to access higher levels of the water column than their competitors, and to be large enough to resist displacement; species employing this response, such as the aptly named Megabalanus, can reach {{convert|7|cm|in|0|abbr=on}} in length.

Competitors may include other barnacles. Balanoids gained their advantage over the chthalamoids in the Oligocene, when they evolved tubular skeletons, which provide better anchorage to the substrate, and allow them to grow faster, undercutting, crushing, and smothering chthalamoids.{{cite journal |last=Stanley |first=Steven M. |title=Predation defeats competition on the seafloor |journal=Paleobiology |date=8 April 2016 |volume=34 |issue=1 |pages=1–21 |doi=10.1666/07026.1 |bibcode=2008Pbio...34....1S |s2cid=83713101 }}

Among the most common predators of barnacles are whelks. They are able to grind through the calcareous exoskeleton and eat the animal inside. Barnacle larvae are consumed by filter-feeding benthic predators including the mussel Mytilus edulis and the ascidian Styela gibbsi.{{cite journal |last1=Cowden |first1=Cynthia |last2=Young |first2=Craig M. |last3=Chia |first3=F. S. |title=Vol. 14: 145-149. 1984 MARINE ECOLOGY - PROGRESS SERIES Mar. Ecol. h o g . Ser. 1 h b l i s h e d January 2 Differential predation on marine invertebrate larvae by two benthic predators |journal=Marine Ecology - Progress Series |date=1984 |volume=14 |pages=145–149 |doi=10.3354/meps014145 |url=https://www.int-res.com/articles/meps/14/m014p145.pdf}} Another predator is the starfish species Pisaster ochraceus.{{cite journal |last1=Harley |first1=C. D. G. |last2=Pankey |first2=M. S. |last3=Wares |first3=J. P. |last4=Grosberg |first4=R. K. |last5=Wonham |first5=M. J. |s2cid=18549566 |title=Color Polymorphism and Genetic Structure in the Sea Star |journal=The Biological Bulletin |date=December 2006 |volume=211 |issue=3 |pages=248–262 |doi=10.2307/4134547 |pmid=17179384 |jstor=4134547 }}{{cite web |last=Holmes |first=Jan |title=Seashore players most successful when they're in their zone |url=http://www.beachwatchers.wsu.edu/island/essays/zonation.htm |year=2002 |work=WSU Beach Watchers |access-date=March 6, 2010 |archive-url=https://web.archive.org/web/20100621224920/http://beachwatchers.wsu.edu/island/essays/zonation.htm |archive-date=2010-06-21 }} A stalked barnacle in the Iblomorpha, Chaetolepas calcitergum, lacks a heavily mineralised shell, but contains a high concentration of toxic bromine; this may serve to deter predators.{{cite news |last=Walker |first=Matt |title=Barnacles become toxic to repel hungry predators |url=http://news.bbc.co.uk/earth/hi/earth_news/newsid_8426000/8426208.stm |website=BBC Earth News |date=22 December 2009 |access-date=18 February 2024}} The turbellarian flatworm Stylochus, a serious predator of oyster spat, has been found in barnacles. Parasites of barnacles include many species of Gregarinasina (alveolate protozoa), a few fungi, a few species of trematodes, and a parasitic castrator isopod, Hemioniscus balani.{{cite journal |last1=Arvy |first1=Lucie |last2=Nigrelli |first2=Ross F. |title=Studies on the biology of barnacles: parasites of Balanus eburneus and B. balanoides from New York Harbor and a review of the parasites and diseases of other Cirripedia |journal=Zoologica |date=1969 |volume=54 |issue=3 |pages=95–102 |url=https://www.biodiversitylibrary.org/page/50998597#page/13/mode/1up}}

File:Balanus improvisus on Mya arenaria shell.jpg, one of the many barnacle taxa described by Charles Darwin, on a bivalve shell ]]

Barnacles were classified by Linnaeus and Cuvier as Mollusca, but in 1830 John Vaughan Thompson published observations showing the metamorphosis of the nauplius and cypris larvae into adult barnacles, and noted that these larvae were similar to those of crustaceans. In 1834, Hermann Burmeister reinterpreted these findings, moving barnacles from the Mollusca to Articulata (in modern terms, annelids + arthropods), showing naturalists that detailed study was needed to reevaluate their taxonomy.{{Cite web |last=Richmond |first=Marsha |title=Darwin's Study of the Cirripedia |url=http://darwin-online.org.uk/EditorialIntroductions/Richmond_cirripedia.html |publisher=Darwin Online |date=January 2007 |access-date=16 June 2012 }}

Charles Darwin took up this challenge in 1846, and developed his initial interest into a major study published as a series of monographs in 1851 and 1854. He undertook this study at the suggestion of his friend the botanist Joseph Dalton Hooker, namely to thoroughly understand at least one species before making the generalisations needed for his theory of evolution by natural selection.{{Cite journal |last=van Wyhe |first=John |date=2007-05-22 |title=Mind the gap: did Darwin avoid publishing his theory for many years? |url=https://royalsocietypublishing.org/doi/10.1098/rsnr.2006.0171 |journal=Notes and Records of the Royal Society |volume=61 |issue=2 |pages=177–205 |doi=10.1098/rsnr.2006.0171 |s2cid=202574857|url-access=subscription }}

The Royal Society notes that barnacles occupied Darwin, who worked from home, so intensely "that his son assumed all fathers behaved the same way: when visiting a friend he asked, 'Where does your father do his barnacles?'"{{cite web |title=Domestic Science: Victorian Naturalists at Home |url=https://royalsociety.org/science-events-and-lectures/2009/summer-science/victorian-naturalists/ |publisher=Royal Society |access-date=19 February 2024 |archive-url=https://web.archive.org/web/20240219104556/https://royalsociety.org/science-events-and-lectures/2009/summer-science/victorian-naturalists/ |archive-date=19 February 2024 |url-status=dead}} Upon the conclusion of his research, Darwin declared "I hate a barnacle as no man ever did before."{{Cite journal |last=Bromham |first=Lindell |date=2020-10-01 |title=Comparability in evolutionary biology: The case of Darwin's barnacles |url=https://www.degruyter.com/document/doi/10.1515/lingty-2020-2056/html?lang=en |journal=Linguistic Typology |volume=24 |issue=3 |pages=427–463 |doi=10.1515/lingty-2020-2056 |s2cid=222319487 |hdl=1885/274303 |hdl-access=free}}

The oldest definitive fossil barnacle is Praelepas from the mid-Carboniferous, around 330-320 million years ago. Older claimed barnacles such as Priscansermarinus from the Middle Cambrian, some {{Ma|510|500}},{{cite book |last1=Foster |first1=B. A. |last2=Buckeridge |first2=J. S. |year=1987 |title=Barnacle palaeontology |pages=41–63}} In A. J. Southward (ed.), 1987. do not show clear barnacle morphological traits, though Rhamphoverritor from the Silurian Coalbrookdale Formation of England may represent a stem-group barnacle. Barnacles first radiated and became diverse during the Late Cretaceous. Barnacles underwent a second, much larger radiation beginning during the Neogene and still continuing.

File:Megabalanus on breccia (cropped).JPG|Miocene (Messinian) Megabalanus, smothered by sand and fossilised

File:Chesaconcavus top view.jpg|Chesaconcavus, a Miocene barnacle from Maryland

File:Chesaconcavus base detail.jpg|Underside of large Chesaconcavus showing internal plates in bioimmured smaller barnacles

The following cladogram, not fully resolved, shows the phylogenetic relationships of the Cirripedia within Thecostraca as of 2021.

{{clade

|label1=Thecostraca

|1={{clade

|1=Facetotecta

|2={{clade

|label1=Ascothoracida

|1={{clade

|1=Laurida

|2=Dendrogastrida

}}

|label2=Cirripedia

|2={{clade

|1={{clade

|label1=Acrothoracica

|sublabel1=burrowing

|1={{clade

|1=Cryptophialida

|2=Lithoglyptida

}}

}}

|2={{clade

|label1=Thoracica

|sublabel1="goose", etc

|1={{clade

|1=Iblomorpha

|label2=Thoracicalcarea

|2={{clade

|1={{clade

|1=Pollicipedomorpha

|2={{clade

|1=Calanticomorpha

|2=Scalpellomorpha

|3={{clade

|label1=Sessilia

|sublabel1=unstalked

|1={{clade

|1=Verrucomorpha

|2=Balanomorpha

}}

}}

}}

}}

}}

}}

|sublabel2=parasitic

|2=Rhizocephala

}}

}}

}}

}}

}}

{{further|List of Cirripedia genera}}

Over 2,100 species of Cirripedia have been described. Some authorities regard the Cirripedia as a full class or subclass. In 2001, Martin and Davis placed Cirripedia as an infraclass of Thecostraca, and divided it into six orders:{{cite book |last1=Martin |first1=Joel W. |last2=Davis |first2=George E. |title=An Updated Classification of the Recent Crustacea |year=2001 |citeseerx=10.1.1.79.1863 |pages=21–23 |url=https://www.vliz.be/imisdocs/publications/ocrd/121258.pdf}}

• Infraclass Cirripedia Burmeister, 1834
• Superorder Acrothoracica Gruvel, 1905
• Order Pygophora Berndt, 1907
• Order Apygophora Berndt, 1907
• Superorder Rhizocephala Müller, 1862
• Order Kentrogonida Delage, 1884
• Order Akentrogonida Häfele, 1911
• Superorder Thoracica Darwin, 1854
• Order Pedunculata Lamarck, 1818
• Order Sessilia Lamarck, 1818

In 2021, Chan et al. elevated Cirripedia to a subclass of the Thecostraca, and the superorders Acrothoracica, Rhizocephala, and Thoracica to infraclass. The updated classification with 11 orders has been accepted in the World Register of Marine Species.{{cite journal |title=The evolutionary diversity of barnacles, with an updated classification of fossil and living forms |date=2021 |last1=Chan |first1=Benny K. K. |last2=Dreyer |first2=Niklas |last3=Gale |first3=Andy S. |last4=Glenner |first4=Henrik |last5=Ewers-Saucedo |first5=Christine |last6=Pérez-Losada |first6=Marcos |last7=Kolbasov |first7=Gregory A. |last8=Crandall |first8=Keith A. |last9=Høeg |first9=Jens T. |display-authors=6 |journal=Zoological Journal of the Linnean Society |volume=193 |issue=3 |pages=789–846 |doi=10.1093/zoolinnean/zlaa160|doi-access=free |hdl=11250/2990967 |hdl-access=free}}{{cite web |url=http://marinespecies.org/aphia.php?p=taxdetails&id=1082 |title=Cirripedia |website=World Register of Marine Species |publisher=Flanders Marine Institute |access-date=22 August 2021}}

• Subclass Cirripedia Burmeister, 1834
• Infraclass Acrothoracica Gruvel, 1905
• Order Cryptophialida Kolbasov, Newman & Hoeg, 2009
• Order Lithoglyptida Kolbasov, Newman & Hoeg, 2009
• Infraclass Rhizocephala Müller, 1862
• Infraclass Thoracica Darwin, 1854
• Superorder Phosphatothoracica Gale, 2019
• Order Iblomorpha Buckeridge & Newman, 2006
• Order † Eolepadomorpha Chan et al., 2021
• Superorder Thoracicalcarea Gale, 2015
• Order Calanticomorpha Chan et al., 2021
• Order Pollicipedomorpha Chan et al., 2021
• Order Scalpellomorpha Buckeridge & Newman, 2006
• Order † Archaeolepadomorpha Chan et al., 2021
• Order † Brachylepadomorpha Withers, 1923
• (Unranked) Sessilia
• Order Balanomorpha Pilsbry, 1916
• Order Verrucomorpha Pilsbry, 1916

{{main|Biofouling}}

Barnacles are of economic consequence, as they often attach themselves to man-made structures. Particularly in the case of ships, they are classified as fouling organisms. The number and size of barnacles that cover ships can impair their efficiency by causing hydrodynamic drag.{{cite journal |last=Holm |first=E. R. |title=Barnacles and Biofouling |journal=Integrative and Comparative Biology |volume=52 |issue=3 |date=2012-09-01 |doi=10.1093/icb/ics042 |pages=348–355 |pmid=22508866 }}

File:Havstulpan.jpg|Barnacles on a boat propeller

File:Barnacles on a Ship.jpg|Barnacles on a ship. The resulting biofouling creates drag, slowing the ship and reducing its fuel efficiency.

The flesh of some barnacles is routinely consumed by humans, including Japanese goose barnacles (e.g. Capitulum mitella), and goose barnacles (e.g. Pollicipes pollicipes) are a delicacy in Spain and Portugal as well.{{cite journal |last1=Molares |first1=José |last2=Freire |first2=Juan |title=Development and perspectives for community-based management of the goose barnacle (Pollicipes pollicipes) fisheries in Galicia (NW Spain) |journal=Fisheries Research |date=December 2003 |volume=65 |issue=1–3 |pages=485–492 |doi=10.1016/j.fishres.2003.09.034 |hdl=2183/90 |url=http://ruc.udc.es/dspace/bitstream/2183/90/1/Community_based_management_barnacle_fisheries%2520%28Fish%2520Res%25202003%29.pdf |hdl-access=free }} The Chilean giant barnacle Austromegabalanus psittacus is fished, or overfished, in commercial quantities on the Chilean coast, where it is known as the {{lang|es|picoroco}}.{{cite journal |last1=Pitombo |first1=Fabio B. |last2=Pappalardo |first2=Paula |last3=Wares |first3=John P. |last4=Haye |first4=Pilar A. |title=A rose by any other name: systematics and diversity in the Chilean giant barnacle Austromegabalanus psittacus (Molina, 1782) (Cirripedia) |journal=Journal of Crustacean Biology |volume=36 |issue=2 |date=2016-02-23 |doi=10.1163/1937240X-00002403 |pages=180–188}}

MIT researchers have developed an adhesive inspired by the protein-based bioglue produced by barnacles to firmly attach to rocks. The adhesive can form a tight seal to halt bleeding within about 15 seconds of application.{{cite journal |last1=Yuk |first1=Hyunwoo |last2=Wu |first2=Jingjing |last3=Sarrafian |first3=Tiffany L. |last4=Mao |first4=Xinyu |last5=Varela |first5=Claudia E. |last6=Roche |first6=Ellen T. |last7=Griffiths |first7=Leigh G. |last8=Nabzdyk |first8=Christoph S. |last9=Zhao |first9=Xuanhe |display-authors=6 |title=Rapid and coagulation-independent haemostatic sealing by a paste inspired by barnacle glue |journal=Nature Biomedical Engineering |volume=5 |issue=10 |date=2021-08-09 |issn=2157-846X |pmid=34373600 |pmc=9254891 |doi=10.1038/s41551-021-00769-y |pages=1131–1142}}

The stable isotope signals in the layers of barnacle shells can potentially be used as a forensic tracking method{{cite journal |last1=Pearson |first1=Ryan M. |last2=van de Merwe |first2=Jason P. |last3=Gagan |first3=Michael K. |last4=Connolly |first4=Rod M. |date=2020 |title=Unique Post-telemetry Recapture Enables Development of Multi-Element Isoscapes From Barnacle Shell for Retracing Host Movement |journal=Frontiers in Marine Science |volume=7 |doi=10.3389/fmars.2020.00596 |issn=2296-7745 |doi-access=free |hdl=10072/395516 |hdl-access=free}} for whales, loggerhead turtles{{cite journal |last1=Pearson |first1=Ryan M. |last2=van de Merwe |first2=Jason P. |last3=Gagan |first3=Michael K. |last4=Limpus |first4=Colin J. |last5=Connolly |first5=Rod M. |title=Distinguishing between sea turtle foraging areas using stable isotopes from commensal barnacle shells |journal=Scientific Reports |date=25 April 2019 |volume=9 |issue=1 |pages=6565 |doi=10.1038/s41598-019-42983-4 |pmid=31024029 |pmc=6483986 |bibcode=2019NatSR...9.6565P }} and for marine debris, such as shipwrecks or aircraft wreckage.{{cite web |title=Can Barnacles unlock the secrets of MH370 and Turtle migration? |url=https://stem.griffith.edu.au/barnacles/ |website=Griffith Sciences Impact |date=3 August 2015 |access-date=15 July 2019 |archive-date=15 July 2019 |archive-url=https://web.archive.org/web/20190715125134/https://stem.griffith.edu.au/barnacles/ |url-status=dead }}{{cite news |last1=Pandey |first1=Swati |title=Barnacles on debris could provide clues to missing MH370: experts |url=https://www.reuters.com/article/us-malaysia-airlines-crash-barnacles/barnacles-on-debris-could-provide-clues-to-missing-mh370-experts-idUSKCN0Q80PY20150803 |work=Reuters |date=3 August 2015 }}{{cite journal |last1=Pearson |first1=Ryan M. |last2=van de Merwe |first2=Jason P. |last3=Connolly |first3=Rod M. |title=Global oxygen isoscapes for barnacle shells: Application for tracing movement in oceans |journal=Science of the Total Environment |volume=705 |pages=135782 |doi=10.1016/j.scitotenv.2019.135782 |pmid=31787294 |year=2020 |bibcode=2020ScTEn.70535782P |s2cid=208536416}}

{{further|Barnacle goose myth}}

One version of the barnacle goose myth is that the birds emerge fully formed from goose barnacles.{{cite web |url=https://sercblog.si.edu/science-superstition-and-the-goose-barnacle/ |title=Science, Superstition and the Goose Barnacle |first=Kristen |last=Minogue |date=29 January 2013 |publisher=Smithsonian Environmental Research Center |access-date=16 April 2020}}{{cite journal |last=van der Lugt |first=M. |year=2000 |title=Animal légendaire et discours savant médiéval. La barnacle dans tous ses états |language=French |trans-title=Legendary animal and medieval learned discourse: the barnacle in all its states |journal=Micrologus |volume=8 |pages=351–393 |url=https://shs.hal.science/halshs-00175458/file/vanderLugt-BARNACLE.pdf}} The myth, with variants such as that the goose barnacles grow on trees, owes its longstanding popularity to ignorance of bird migration.{{cite book |last=Kenicer |first=G. J. |year=2020 |title=Plant Magic |location=Edinburgh |publisher=Royal Botanic Garden Edinburgh |pages=150–151}}{{cite book |last=Mayntz |first=M. |year=2020 |title=Migration: Exploring the Remarkable Journeys of Birds |location=London |publisher=Quadrille |pages=110–111}}{{cite journal |last1=Lappo |first1=E. G. |last2=Popovkina |first2=A. B. |last3=Mooij |first3=J. H. |year=2019 |title=About geese growing on trees: the Medieval interpretation of the Barnacle and Brent goose origin |journal=Goose Bulletin |issue=24 |pages=8–21 |url=https://cms.geese.org/sites/default/files/Goose%20Bulletin24.pdf}} The myth survived to modern times through bestiaries.{{cite journal |last=Sprouse |first=S. J. |year=2015 |title=The Associative Branches of the Irish Barnacle: Gerald of Wales and the Natural World |journal=Hortulus |volume=11 |issue=2}}

More recently, Barnacle Bill became a "comic folktype" of a seaman, with a drinking song{{cite book |last=Bronner |first=Simon J. |title=The Practice of Folklore |chapter=“Who’s That Knocking at My Door?”: Barnacle Bill Again and Again |publisher=University Press of Mississippi |date=2019-08-15 |isbn=978-1-4968-2262-8 |doi=10.14325/mississippi/9781496822628.003.0007 |pages=152–198|s2cid=212949243 }} and several films (a 1930 animated short with Betty Boop,{{cite book |last=Lenburg |first=Jeff |title=The Encyclopedia of Animated Cartoons |date=1999 |publisher=Checkmark Books |isbn=0-8160-3831-7 |page=142}} a 1935 British drama,{{cite web |title=Barnacle Bill (1935) |url=http://ftvdb.bfi.org.uk/sift/title/143535 |publisher=BFI |archive-url=https://web.archive.org/web/20090116104139/http://ftvdb.bfi.org.uk/sift/title/143535 |access-date=18 February 2024|archive-date=2009-01-16 }} a 1941 feature with Wallace Beery,{{cite web |title=Barnacle Bill (1941) |url=https://www.allmovie.com/movie/barnacle-bill-vm473797 |website=AllMovie |access-date=18 February 2024}} and a 1957 Ealing comedy{{Cite web |title=Barnacle Bill |url=https://collections-search.bfi.org.uk/web/Details/ChoiceFilmWorks/150025183 |access-date=4 February 2024 |website=British Film Institute Collections Search}}) named after him.

The political reformer John W. Gardner likened middle managers who settle into a comfortable position and "have stopped learning or growing" to the barnacle, who "is confronted with an existential decision about where it's going to live. Once it decides... it spends the rest of its life with its head cemented to a rock".{{cite web |last=Gardner |first=John W. |author-link=John W. Gardner |title=John Gardner's writings: "Personal Renewal" |url=https://www.pbs.org/johngardner/sections/writings_speech_1.html |publisher=PBS |access-date=19 February 2024 |archive-url=https://web.archive.org/web/20011105005848/https://www.pbs.org/johngardner/sections/writings_speech_1.html |archive-date=5 November 2001 |date=10 November 1990 |quote=Delivered to McKinsey & Company, Phoenix, AZ November 10, 1990}}

File:Percebes.iguaria.jpg|A dish of goose barnacles in a restaurant in Spain

File:The "Barnacle Geese" being born then swimming away. Wellcome M0005645.jpg|Barnacle geese being "born" from {{lang|la|conchae anatiferae}} (goose-bearing shells) by the sea, then swimming away. Ulisse Aldrovandi, 16th century

File:Wallace Beery in Barnacle Bill (1941).png|Wallace Beery as the title character in Barnacle Bill (1941)

{{Reflist|30em}}

• {{cite book |series=Crustacean Issues |volume=5 |title=Barnacle Biology |editor=Alan J. Southward |isbn=978-90-6191-628-4 |publisher=CRC Press / A. A. Balkema |location=Leiden, Netherlands |ref=refSouthward |date=1987-06-01 }}

• {{cite book |url=http://darwin-online.org.uk/content/frameset?itemID=F339.1&viewtype=side&pageseq=1 |author=Darwin, C. R. |year=1852 |series=A monograph of the sub-class Cirripedia, with figures of all the species |volume=1 |title=The Lepadidæ |publisher=Ray Society |location=London|author-link=Charles Darwin |ref=none}}
• {{cite book |url=http://darwin-online.org.uk/content/frameset?itemID=F339.2&viewtype=text&pageseq=1 |author=Darwin, C. R. |year=1854 |series=A monograph of the sub-class Cirripedia, with figures of all the species |volume=2 |title=The Balanidæ, (or sessile cirripedes); the Verrucidæ, etc. |publisher=Ray Society |location=London|author-link=Charles Darwin |ref=none}}
• {{Cite EB1911 |last=Calman |first=William Thomas |author-link=William Thomas Calman |wstitle=Barnacle |volume=3 |page=409 |short=x |ref=none}}
• {{Cite EB1911 |first=Thomas Roscoe Rede |last=Stebbing |author-link=Thomas Roscoe Rede Stebbing |wstitle=Thyrostraca |volume=26 |pages=905–906 |short=x |ref=none}}

{{Commons category|Cirripedia}}

{{Wikispecies|Cirripedia}}

• [http://www.mesa.edu.au/friends/seashores/barnacles.html Barnacles] from the Marine Education Society of Australasia
• [http://www.iberianature.com/material/barnacles.htm Barnacles in Spain] Article on barnacles in Spain, and their collection and gastronomy.

{{Arthropods}}

{{Taxonbar|from=Q220457}}

{{Authority control}}

Category:Parasitic crustaceans

Category:Maxillopoda

Category:Articles containing video clips

Category:Taxa described in 1834

Category:Taxa named by Hermann Burmeister