Barnacle
Template:Short description {{#invoke:other uses|otheruses}} Template:Good article Template:Automatic taxobox
Barnacles are arthropods of the subclass Cirripedia in the subphylum Crustacea. They are related to crabs and lobsters, with similar nauplius larvae. Barnacles are exclusively marine invertebrates; many species live in shallow and tidal waters. Some 2,100 species have been described.
Barnacle adults are sessile; most are suspension feeders with hard calcareous shells, but the Rhizocephala are specialized parasites of other crustaceans, with reduced bodies. Barnacles have existed since at least the mid-Carboniferous, some 325 million years ago.
In folklore, barnacle geese were once held to emerge fully formed from goose barnacles. Both goose barnacles and the Chilean giant barnacle are fished and eaten. Barnacles are economically significant as biofouling on ships, where they cause hydrodynamic drag, reducing efficiency.
EtymologyEdit
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.<ref name="Müller 1871">Template:Cite book</ref><ref name="EtymDict"/> 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.<ref name="EtymDict">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite encyclopedia</ref>
The name {{#invoke:Lang|lang}} comes from the Latin words cirritus "curly" from cirrus "curl"<ref>Template:Cite encyclopedia</ref> and pedis from pes "foot".<ref>Template:Cite encyclopedia</ref> The two words together mean "curly-footed", alluding to the curved legs used in filter-feeding.<ref>Template:Cite book</ref>
DescriptionEdit
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.<ref name=Doyle1997>Template:Cite journal</ref>
Anatomy and physiologyEdit
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.<ref name="OceanFacts"/>
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.<ref>Template:Cite journal</ref>Template:Rp This natural cement can withstand a pulling strength of Template:Convert and a sticking strength of Template:Convert.<ref name="OceanFacts">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
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.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The blood vascular system is minimal.<ref>Template:Cite book In A. J. Southward (ed.), 1987.</ref> Similarly, they have no gills, absorbing oxygen from the water through the cirri and the surface of the body.<ref name="Monterey">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> The excretory organs of barnacles are maxillary glands.<ref name="White Walker 1981">Template:Cite journal</ref>
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.<ref>Template:Cite journal</ref> The photoreceptors are likely only capable of sensing the difference between light and dark.<ref name=IZ>Template:Cite book</ref> This eye is derived from the primary naupliar eye.<ref>Template:Cite journal</ref>
Life cycleEdit
Barnacles pass through two distinct larval stages, the nauplius and the cyprid, before developing into a mature adult.
Nauplius larvaEdit
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.<ref name="Newman">Template:Cite book</ref><ref>Template:Cite book</ref> All but the first instars are filter feeders.<ref name=PooreSyme>Template:Cite book</ref>
- Elminius modestus nauplius.jpg
Nauplius larva of Elminius modestus
- Cirripedia nauplius.png
Nauplius with fronto-lateral horns<ref>Template:Cite journal</ref>
Cypris larvaEdit
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.<ref>Template:Cite journal</ref> It is not a feeding stage; its role is to find a suitable place to settle, since the adults are sessile.<ref name="Newman"/> 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.<ref name="Anderson">Template:Cite book</ref> 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.<ref name="Anderson"/>
- Balanus improvisus, cypris (rotated).jpg
Cypris larva of Amphibalanus improvisus
- Barnacles Cypris anatomy diagram vecorized.svg
Anatomy of cypris larva
AdultEdit
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.<ref>Template:Cite book In A. J. Southward (ed.), 1987.</ref>
Sexual reproductionEdit
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.<ref name="Museum Victoria">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite book In A. J. Southward (ed.), 1987.</ref>
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,<ref name="Museum Victoria"/> up to eight times their body length, though on exposed coasts the penis is shorter and thicker.<ref name="Callaway 2009">Template:Cite magazine</ref> The mating of acorn barnacles is described as pseudocopulation.<ref name="Barazandeh Davis Neufeld Coltman 2013"/><ref name="Bishop Pemberton 2005">Template:Cite journal</ref>
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.<ref name="Barazandeh Davis Neufeld Coltman 2013">Template:Cite journal</ref>
Rhizocephalan barnacles had been considered hermaphroditic, but their males inject themselves into females' bodies, degrading to little more than sperm-producing cells.<ref name="Dale 2013">Template:Cite book</ref>
EcologyEdit
Filter feedingEdit
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.<ref name=Doyle1997/><ref>Template:Cite book</ref>
- Giant Acorn Barnacle, Embarcadero, Morro Bay, CA, US imported from iNaturalist photo 149595197.jpg
Balanus nubilus with cirri extended
- Entenmuscheln.jpg
Goose barnacles, with their cirri extended for feeding
- Scalpellid barnacle feeding.jpg
A scalpellid barnacle feeding
- Semibalanus balanoides upernavik 2007-07-05.ogv
Semibalanus balanoides filter-feeding by projecting and retracting their cirri
Species-specific zonesEdit
Although they have been found at water depths to Template:Convert,<ref name=Doyle1997/> most barnacles inhabit shallow waters, with 75% of species living in water depths less than Template:Convert,<ref name=Doyle1997/> and 25% inhabiting the intertidal zone.<ref name=Doyle1997/> 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.<ref name=Doyle1997/>
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.<ref name="Buckeridge 2012">Template:Cite journal</ref> Their hard shells are assumed by zoologists to have evolved as an anti-predator adaptation.<ref name="Zimmer Ferrier Zimmer 2021">Template:Cite journal</ref>
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.<ref>Template:Cite journal</ref>
ParasitismEdit
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.<ref name="Hosie 2018">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> <ref name=IZ/>
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.<ref>Template:Cite journal</ref>
CompetitorsEdit
Barnacles are displaced by limpets and mussels, which compete for space.<ref name=Doyle1997/> 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.<ref name=Doyle1997/> 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 Template:Convert in length.<ref name=Doyle1997/>
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.<ref name=Stanley2008>Template:Cite journal</ref>
Predators and parasitesEdit
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.<ref>Template:Cite journal</ref> Another predator is the starfish species Pisaster ochraceus.<ref>Template:Cite journal</ref><ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> 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.<ref>Template:Cite news</ref> The turbellarian flatworm Stylochus, a serious predator of oyster spat, has been found in barnacles.<ref name="Arvy Nigrelli 1969"/> 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.<ref name="Arvy Nigrelli 1969">Template:Cite journal</ref>
History of taxonomyEdit
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.<ref name="Richmond 2007">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
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.<ref name="Richmond 2007"/> 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.<ref name="Wyhe 2007">Template:Cite journal</ref> 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?'"<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> Upon the conclusion of his research, Darwin declared "I hate a barnacle as no man ever did before."<ref name="Wyhe 2007"/><ref name="Bromham 2020">Template:Cite journal</ref>
EvolutionEdit
Fossil recordEdit
The oldest definitive fossil barnacle is Praelepas from the mid-Carboniferous, around 330-320 million years ago.<ref name="Chan Dreyer Gale 2021"/> Older claimed barnacles such as Priscansermarinus from the Middle Cambrian, some Template:Ma,<ref name=Foster1987>Template:Cite book In A. J. Southward (ed.), 1987.</ref> 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.<ref name="Chan Dreyer Gale 2021"/>
- Megabalanus on breccia (cropped).JPG
Miocene (Messinian) Megabalanus, smothered by sand and fossilised
- Chesaconcavus top view.jpg
Chesaconcavus, a Miocene barnacle from Maryland
- Chesaconcavus base detail.jpg
Underside of large Chesaconcavus showing internal plates in bioimmured smaller barnacles
PhylogenyEdit
The following cladogram, not fully resolved, shows the phylogenetic relationships of the Cirripedia within Thecostraca as of 2021.<ref name="Chan Dreyer Gale 2021"/>
TaxonomyEdit
Over 2,100 species of Cirripedia have been described.<ref name="Chan Dreyer Gale 2021"/> 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:<ref>Template:Cite book</ref>
- 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
- Superorder Acrothoracica Gruvel, 1905
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.<ref name="Chan Dreyer Gale 2021">Template:Cite journal</ref><ref name=worms>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
- 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
- Superorder Phosphatothoracica Gale, 2019
- Infraclass Acrothoracica Gruvel, 1905
Relationship with humansEdit
BiofoulingEdit
{{#invoke:Labelled list hatnote|labelledList|Main article|Main articles|Main page|Main pages}}
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.<ref name="Holm 2012">Template:Cite journal</ref>
- Havstulpan.jpg
Barnacles on a boat propeller
- Barnacles on a Ship.jpg
Barnacles on a ship. The resulting biofouling creates drag, slowing the ship and reducing its fuel efficiency.<ref name="Holm 2012"/>
As foodEdit
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.<ref name="Molares">Template:Cite journal</ref> The Chilean giant barnacle Austromegabalanus psittacus is fished, or overfished, in commercial quantities on the Chilean coast, where it is known as the {{#invoke:Lang|lang}}.<ref name="Pitombo Pappalardo Wares Haye 2016 pp. 180–188">Template:Cite journal</ref>
Technological applicationsEdit
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.<ref>Template:Cite journal</ref>
The stable isotope signals in the layers of barnacle shells can potentially be used as a forensic tracking method<ref>Template:Cite journal</ref> for whales, loggerhead turtles<ref>Template:Cite journal</ref> and for marine debris, such as shipwrecks or aircraft wreckage.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite news</ref><ref>Template:Cite journal</ref>
In cultureEdit
One version of the barnacle goose myth is that the birds emerge fully formed from goose barnacles.<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref><ref>Template:Cite journal</ref> The myth, with variants such as that the goose barnacles grow on trees, owes its longstanding popularity to ignorance of bird migration.<ref>Template:Cite book</ref><ref>Template:Cite book</ref><ref>Template:Cite journal</ref> The myth survived to modern times through bestiaries.<ref>Template:Cite journal</ref>
More recently, Barnacle Bill became a "comic folktype"<ref name="Bronner 2019"/> of a seaman, with a drinking song<ref name="Bronner 2019">Template:Cite book</ref> and several films (a 1930 animated short with Betty Boop,<ref>Template:Cite book</ref> a 1935 British drama,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> a 1941 feature with Wallace Beery,<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> and a 1957 Ealing comedy<ref name="BFIsearch">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>) 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".<ref name="Gardner 1990">{{#invoke:citation/CS1|citation |CitationClass=web }}</ref>
- Percebes.iguaria.jpg
A dish of goose barnacles in a restaurant in Spain
- The "Barnacle Geese" being born then swimming away. Wellcome M0005645.jpg
lang}} (goose-bearing shells) by the sea, then swimming away. Ulisse Aldrovandi, 16th century
- Wallace Beery in Barnacle Bill (1941).png
Wallace Beery as the title character in Barnacle Bill (1941)
ReferencesEdit
SourcesEdit
Further readingEdit
External linksEdit
- Barnacles from the Marine Education Society of Australasia
- Barnacles in Spain Article on barnacles in Spain, and their collection and gastronomy.
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