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A barnacle is a type of
arthropod Arthropods (, (gen. ποδός)) are invertebrate animals with an exoskeleton, a Segmentation (biology), segmented body, and paired jointed appendages. Arthropods form the phylum Arthropoda. They are distinguished by their jointed limbs and Arth ...
constituting the subclass Cirripedia in the subphylum
Crustacea Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapods, seed shrimp, branchiopods, fish lice, krill, remipedes, isopods, barnacles, copepods, amphipods and mantis shrimp. The crustacean gro ...
, and is hence related to
crab Crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" (abdomen) ( el, βραχύς , translit=brachys = short, / = tail), usually hidden entirely under the thorax. They live in all the ...
s and
lobster Lobsters are a family (biology), family (Nephropidae, Synonym (taxonomy), synonym Homaridae) of marine crustaceans. They have long bodies with muscular tails and live in crevices or burrows on the sea floor. Three of their five pairs of legs ...
s. Barnacles are exclusively marine, and tend to live in shallow and tidal waters, typically in erosive settings. They are
sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...
(nonmobile) and most are suspension feeders, but those in
infraclass In biological classification, class ( la, classis) is a taxonomic rank, as well as a taxonomic unit, a taxon, in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life, domain, kingdom ...
Rhizocephala Rhizocephala are derived barnacles that parasitise mostly decapod crustaceans, but can also infest Peracarida, mantis shrimps and thoracican barnacles, and are found from the deep ocean to freshwater. Together with their sister groups Thoracica ...
are highly specialized parasites on crustaceans. They have four
nekton Nekton or necton (from the ) refers to the actively swimming aquatic organisms in a body of water. The term was proposed by German biologist Ernst Haeckel to differentiate between the active swimmers in a body of water, and the passive organisms ...
ic (active swimming) larval stages. Around 1,000 barnacle
species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...
are currently known. The name is
Latin Latin (, or , ) is a classical language belonging to the Italic branch of the Indo-European languages. Latin was originally a dialect spoken in the lower Tiber area (then known as Latium) around present-day Rome, but through the power of the ...
, meaning "curl-footed". The study of barnacles is called cirripedology.


Description

Barnacles are encrusters, attaching themselves temporarily to a hard substrate or a
symbiont Symbiosis (from Greek , , "living together", from , , "together", and , bíōsis, "living") is any type of a close and long-term biological interaction between two different biological organisms, be it mutualistic, commensalistic, or parasit ...
such as a whale (
whale barnacle Whale barnacles are species of acorn barnacle that belong to the family Coronulidae. They typically attach to baleen whales, and sometimes settle on toothed whales. The whale barnacles diverged from the turtle barnacles about three million year ...
s), a sea snake (''
Platylepas ophiophila ''Platylepas ophiophila'', commonly known as the sea snake barnacle, is a species of barnacle in the family Platylepadidae. It is native to the Indo-Pacific Ocean where it lives as a symbiont of a sea snake. Ecology ''Platylepas ophiophila'' i ...
''), or another crustacean, like a crab or a lobster (
Rhizocephala Rhizocephala are derived barnacles that parasitise mostly decapod crustaceans, but can also infest Peracarida, mantis shrimps and thoracican barnacles, and are found from the deep ocean to freshwater. Together with their sister groups Thoracica ...
). The most common among them, "acorn barnacles" (
Sessilia Sessilia is an unranked clade of barnacles, comprising the barnacles without stalks, or acorn barnacles. They form a monophyletic group and are probably derived from stalked or goose barnacles. Sessilia is divided into two orders. The Verrucomo ...
), are
sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...
where they grow their shells directly onto the substrate. Pedunculate barnacles (
goose barnacle Goose barnacles, also called stalked barnacles or gooseneck barnacles, are filter-feeding crustaceans that live attached to hard surfaces of rocks and flotsam in the ocean intertidal zone. Goose barnacles formerly made up the taxonomic order Ped ...
s and others) attach themselves by means of a stalk. Free-living 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 able to withstand a pulling strength of per square inch and an sticking strength of per square inch. A ring of plates surrounds the body, homologous with the
carapace A carapace is a Dorsum (biology), dorsal (upper) section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tor ...
of other crustaceans. These consist of the
rostrum Rostrum may refer to: * Any kind of a platform for a speaker: **dais **pulpit * Rostrum (anatomy), a beak, or anatomical structure resembling a beak, as in the mouthparts of many sucking insects * Rostrum (ship), a form of bow on naval ships * Ros ...
, two lateral plates, two carinolaterals, and a carina. In sessile barnacles, the apex of the ring of plates is covered by an operculum, which may be recessed into the carapace. The plates are held together by various means, depending on species, in some cases being solidly fused. Inside the carapace, the animal lies on its stomach, projecting its limbs downwards. Segmentation is usually indistinct, and the body is more or less evenly divided between the head and
thorax The thorax or chest is a part of the anatomy of humans, mammals, and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main divisions of the cre ...
, with little, if any,
abdomen The abdomen (colloquially called the belly, tummy, midriff, tucky or stomach) is the part of the body between the thorax (chest) and pelvis, in humans and in other vertebrates. The abdomen is the front part of the abdominal segment of the torso. ...
. Adult barnacles have few appendages on their heads, with only a single, vestigial pair of antennae, attached to the cement gland. The eight pairs of thoracic limbs are referred to as "
cirri Giovanni Battista Cirri (1 October 1724 – 11 June 1808) was an Italian cellist and composer in the 18th century. Biography Cirri was born in Forlì in the Emilia-Romagna Region of Italy. He had his first musical training with his brother ...
" which are feathery and very long, the cirri extend to filter food, such as plankton, from the water and move it towards the mouth. Barnacles have no true
heart The heart is a muscular organ in most animals. This organ pumps blood through the blood vessels of the circulatory system. The pumped blood carries oxygen and nutrients to the body, while carrying metabolic waste such as carbon dioxide t ...
, although a sinus close to the
esophagus The esophagus (American English) or oesophagus (British English; both ), non-technically known also as the food pipe or gullet, is an organ in vertebrates through which food passes, aided by peristaltic contractions, from the pharynx to the ...
performs a similar function, with blood being pumped through it by a series of muscles. The blood vascular system is minimal. Similarly, they have no
gill A gill () is a respiratory organ that many aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow respiration on land provided they are ...
s, absorbing
oxygen Oxygen is the chemical element with the symbol O and atomic number 8. It is a member of the chalcogen group in the periodic table, a highly reactive nonmetal, and an oxidizing agent that readily forms oxides with most elements as wel ...
from the water through their limbs and the inner membrane of their carapaces. The excretory organs of barnacles are maxillary glands. The main sense of barnacles appears to be touch, with the hairs on the limbs being especially sensitive. The adult also has three photoreceptors (ocelli), one median and two lateral. These photoreceptors 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. The photoreceptors are likely only capable of sensing the difference between light and dark. This eye is derived from the primary
naupliar eye Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The ...
.


Life cycle

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


Nauplius

A
fertilised egg A zygote (, ) is a eukaryotic cell formed by a fertilization event between two gametes. The zygote's genome is a combination of the DNA in each gamete, and contains all of the genetic information of a new individual organism. In multicellula ...
hatches into a nauplius: a one-eyed larva comprising a head and a
telson The telson () is the posterior-most division of the body of an arthropod. Depending on the definition, the telson is either considered to be the final segment of the arthropod body, or an additional division that is not a true segment on accou ...
, without a thorax or abdomen. This undergoes six moults, passing through five
instar An instar (, from the Latin '' īnstar'', "form", "likeness") is a developmental stage of arthropods, such as insects, between each moult (''ecdysis''), until sexual maturity is reached. Arthropods must shed the exoskeleton in order to grow or ass ...
s, 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
seta In biology, setae (singular seta ; from the Latin word for "bristle") are any of a number of different bristle- or hair-like structures on living organisms. Animal setae Protostomes Annelid setae are stiff bristles present on the body. Th ...
e.


Cyprid

The cyprid larva is the last larval stage before adulthood. It is not a feeding stage; its role is to find a suitable place to settle, since the adults are
sessile Sessility, or sessile, may refer to: * Sessility (motility), organisms which are not able to move about * Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant * Sessility (medicine), tumors and polyps that ...
. The cyprid stage lasts from days to weeks. It explores potential surfaces with modified antennules; once it has found a potentially suitable spot, it attaches head-first using its antennules and a secreted glycoproteinous substance. Larvae assess surfaces based upon their surface texture, chemistry, relative wettability, color, and the presence or absence and composition of a surface
biofilm A biofilm comprises any syntrophic consortium of microorganisms in which cells stick to each other and often also to a surface. These adherent cells become embedded within a slimy extracellular matrix that is composed of extracellular ...
; swarming species are also more likely to attach near other barnacles. As the larva exhausts its finite 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 Metamorphosis is a biological process by which an animal physically develops including birth or hatching, involving a conspicuous and relatively abrupt change in the animal's body structure through cell growth and differentiation. Some inse ...
into a juvenile barnacle.


Adult

Typical
acorn barnacle Acorn barnacle and acorn shell are Common name, vernacular names for certain types of stalkless barnacles, generally excluding goose barnacles, stalked or gooseneck barnacles. As adults they are typically cone-shaped, symmetrical, and attached to r ...
s 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 In biology, moulting (British English), or molting (American English), also known as sloughing, shedding, or in many invertebrates, ecdysis, is the manner in which an animal routinely casts off a part of its body (often, but not always, an outer ...
; however, like all
ecdysozoa Ecdysozoa () is a group of protostome animals, including Arthropoda (insects, chelicerata, crustaceans, and myriapods), Nematoda, and several smaller phyla. They were first defined by Aguinaldo ''et al.'' in 1997, based mainly on phylogenetic tr ...
ns, the barnacle itself will still moult its
cuticle A cuticle (), or cuticula, is any of a variety of tough but flexible, non-mineral outer coverings of an organism, or parts of an organism, that provide protection. Various types of "cuticle" are non- homologous, differing in their origin, structu ...
.


Sexual reproduction

Most barnacles are
hermaphroditic In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have separ ...
, although a few species are
gonochoric In biology, gonochorism is a sexual system where there are only two sexes and each individual organism is either male or female. The term gonochorism is usually applied in animal species, the vast majority of which are gonochoric. Gonochorism c ...
or
androdioecious Androdioecy is a reproductive system characterized by the coexistence of males and hermaphrodites. Androdioecy is rare in comparison with the other major reproductive systems: dioecy, gynodioecy and hermaphroditism. In animals, androdioecy has bee ...
. 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. The sessile lifestyle of barnacles makes
sexual reproduction Sexual reproduction is a type of reproduction that involves a complex life cycle in which a gamete ( haploid reproductive cells, such as a sperm or egg cell) with a single set of chromosomes combines with another gamete to produce a zygote tha ...
difficult, as the organisms cannot leave their shells to mate. To facilitate genetic transfer between isolated individuals, barnacles have extraordinarily long
penis A penis (plural ''penises'' or ''penes'' () is the primary sexual organ that male animals use to inseminate females (or hermaphrodites) during copulation. Such organs occur in many animals, both vertebrate and invertebrate, but males do n ...
es⁠. Barnacles probably have the largest penis to body size ratio of the animal kingdom, up to eight times their body length. Barnacles can also reproduce through a method called spermcasting, in which the male barnacle releases his sperm into the water and females pick it up and fertilise their eggs. The
Rhizocephala Rhizocephala are derived barnacles that parasitise mostly decapod crustaceans, but can also infest Peracarida, mantis shrimps and thoracican barnacles, and are found from the deep ocean to freshwater. Together with their sister groups Thoracica ...
superorder used to be considered hermaphroditic, but it turned out that its males inject themselves into the female's body, degrading to the condition of nothing more than sperm-producing cells.


Ecology

Most barnacles are suspension feeders; they dwell continually in their shells, which are usually constructed of six plates, and reach into the water column with modified legs. These feathery appendages beat rhythmically to draw
plankton Plankton are the diverse collection of organisms found in Hydrosphere, water (or atmosphere, air) that are unable to propel themselves against a Ocean current, current (or wind). The individual organisms constituting plankton are called plankt ...
and detritus into the shell for consumption. Other members of the class have quite a different mode of life. For example, members of the
superorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
Rhizocephala Rhizocephala are derived barnacles that parasitise mostly decapod crustaceans, but can also infest Peracarida, mantis shrimps and thoracican barnacles, and are found from the deep ocean to freshwater. Together with their sister groups Thoracica ...
, including the
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
''
Sacculina ''Sacculina'' is a genus of barnacles that is a parasitic castrator of crabs. They belong to a group called ''Rhizocephala''. The adults bear no resemblance to the barnacles that cover ships and piers; they are recognised as barnacles because ...
'', are
parasitic Parasitism is a close relationship between species, where one organism, the parasite, lives on or inside another organism, the host, causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson has c ...
and live within crabs. Although they have been found at water depths to , most barnacles inhabit shallow waters, with 75% of species living in water depths less than , and 25% inhabiting the
intertidal zone The intertidal zone, also known as the foreshore, is the area above water level at low tide and underwater at high tide (in other words, the area within the tidal range). This area can include several types of habitats with various species o ...
. 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 possess two plates which they can slide across their apertures when not feeding. These plates also protect against predation. Barnacles are displaced by
limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...
s and
mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...
s, which compete for space. They also have numerous predators. 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 ''Megabalanus'' is a genus of barnacles in the family Balanidae. Members of the genus grow to in length and inhabit the lower intertidal zone. Morphology ''Megabalanus'' is an acorn barnacle, a sessile crustacean that secretes a calcium carbon ...
'', can reach in length; other species may grow larger still (''
Austromegabalanus psittacus ''Austromegabalanus psittacus'', the giant barnacle or ' as it is known in Spanish, is a species of large barnacle native to the coasts of southern Peru, all of Chile and southern Argentina. It inhabits the littoral and intertidal zones of rocky ...
''). Competitors may include other barnacles, and disputed evidence indicates balanoid barnacles competitively displaced chthalamoid 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. Among the most common predators on barnacles are
whelk Whelk (also known as scungilli) is a common name applied to various kinds of sea snail. Although a number of whelks are relatively large and are in the family Buccinidae (the true whelks), the word ''whelk'' is also applied to some other marine ...
s. They are able to grind through the calcareous exoskeletons of barnacles and feed on the softer inside parts.
Mussel Mussel () is the common name used for members of several families of bivalve molluscs, from saltwater and Freshwater bivalve, freshwater habitats. These groups have in common a shell whose outline is elongated and asymmetrical compared with other ...
s also prey on barnacle larvae. Another predator on barnacles is the starfish species ''
Pisaster ochraceus ''Pisaster ochraceus'', generally known as the purple sea star, ochre sea star, or ochre starfish, is a common seastar found among the waters of the Pacific Ocean. Identified as a keystone species, ''P. ochraceus'' is considered an important indi ...
''. File:CornishBarnacles.JPG, Barnacles and
limpet Limpets are a group of aquatic snails that exhibit a conical shell shape (patelliform) and a strong, muscular foot. Limpets are members of the class Gastropoda, but are polyphyletic, meaning the various groups called "limpets" descended indep ...
s compete for space in the intertidal zone File:Entenmuscheln.jpg, Goose barnacles, with their cirri extended for feeding File:Chesaconcavus base detail.jpg, Underside of large ''Chesaconcavus'' sp. (
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
) showing internal plates in bioimmured smaller barnacles
The anatomy of parasitic barnacles is generally simpler than that of their free-living relatives. They have no carapace or limbs, having only unsegmented sac-like bodies. Such barnacles feed by extending thread-like rhizomes of living cells into their hosts' bodies from their points of attachment.


History of taxonomy

Barnacles were originally classified by
Linnaeus Carl Linnaeus (; 23 May 1707 – 10 January 1778), also known after his ennoblement in 1761 as Carl von Linné Blunt (2004), p. 171. (), was a Swedish botanist, zoologist, taxonomist, and physician who formalised binomial nomenclature, the ...
and
Cuvier Jean Léopold Nicolas Frédéric, Baron Cuvier (; 23 August 1769 – 13 May 1832), known as Georges Cuvier, was a French naturalist and zoologist, sometimes referred to as the "founding father of paleontology". Cuvier was a major figure in nat ...
as
Mollusca Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda, the members of which are known as molluscs or mollusks (). Around 85,000  extant species of molluscs are recognized. The number of fossil species is esti ...
, but in 1830
John Vaughan Thompson John Vaughan Thompson FLS (19 November 1779 – 21 January 1847) was a British military surgeon, marine biologist, zoologist, botanist, and published naturalist. Early years John Vaughan Thompson was born in British controlled Brooklyn on Lon ...
published observations showing the metamorphosis of the nauplius and cypris larvae into adult barnacles, and noted how these larvae were similar to those of crustaceans. In 1834
Hermann Burmeister Karl Hermann Konrad Burmeister (also known as Carlos Germán Conrado Burmeister) (15 January 1807 – 2 May 1892) was a German Argentine zoologist, entomologist, herpetologist, botany, botanist, and coleopterologist. He served as a professor at ...
published further information, reinterpreting these findings. The effect was to move barnacles from the
phylum In biology, a phylum (; plural: phyla) is a level of classification or taxonomic rank below kingdom and above class. Traditionally, in botany the term division has been used instead of phylum, although the International Code of Nomenclature f ...
of Mollusca to Articulata, showing naturalists that detailed study was needed to reevaluate their
taxonomy Taxonomy is the practice and science of categorization or classification. A taxonomy (or taxonomical classification) is a scheme of classification, especially a hierarchical classification, in which things are organized into groups or types. ...
.
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
took up this challenge in 1846, and developed his initial interest into a major study published as a series of
monographs A monograph is a specialist work of writing (in contrast to reference works) or exhibition on a single subject or an aspect of a subject, often by a single author or artist, and usually on a scholarly subject. In library cataloging, ''monograph ...
in 1851 and 1854. Darwin undertook this study, at the suggestion of his friend
Joseph Dalton Hooker Sir Joseph Dalton Hooker (30 June 1817 – 10 December 1911) was a British botanist and explorer in the 19th century. He was a founder of geographical botany and Charles Darwin's closest friend. For twenty years he served as director of t ...
, to thoroughly understand at least one species before making the generalisations needed for his theory of
evolution Evolution is change in the heritable characteristics of biological populations over successive generations. These characteristics are the expressions of genes, which are passed on from parent to offspring during reproduction. Variation ...
by
natural selection Natural selection is the differential survival and reproduction of individuals due to differences in phenotype. It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations. Charle ...
.


Classification

Some authorities regard the Cirripedia as a full
class Class or The Class may refer to: Common uses not otherwise categorized * Class (biology), a taxonomic rank * Class (knowledge representation), a collection of individuals or objects * Class (philosophy), an analytical concept used differentl ...
or subclass, and the orders listed above are sometimes treated as
superorder Order ( la, ordo) is one of the eight major hierarchical taxonomic ranks in Linnaean taxonomy. It is classified between family and class. In biological classification, the order is a taxonomic rank used in the classification of organisms and ...
s. In 2001, Martin and Davis placed Cirripedia as an infraclass of
Thecostraca Thecostraca is a class of marine invertebrates containing over 2,200 described species. Many species have planktonic larvae which become sessile or parasitic as adults. The most important subgroup are the barnacles (subclass Cirripedia), constit ...
and divided it into six orders: *Infraclass Cirripedia Burmeister, 1834 ** Superorder
Acrothoracica The Acrothoracica are an infraclass of barnacles. Acrothoracicans bore into calcareous material such as mollusc shells, coral, crinoids or hardgrounds, producing a slit-like hole in the surface known by the trace fossil name ''Rogerella''. Acr ...
Gruvel, 1905 *** Order Pygophora Berndt, 1907 *** Order Apygophora Berndt, 1907 ** Superorder
Rhizocephala Rhizocephala are derived barnacles that parasitise mostly decapod crustaceans, but can also infest Peracarida, mantis shrimps and thoracican barnacles, and are found from the deep ocean to freshwater. Together with their sister groups Thoracica ...
Müller, 1862 *** Order Kentrogonida Delage, 1884 *** Order Akentrogonida Häfele, 1911 ** Superorder
Thoracica Thoracica is an infraclass of crustaceans which contains the most familiar species of barnacles found on rocky coasts, such as '' Semibalanus balanoides'' and ''Chthamalus stellatus''. They have six well-developed limbs, and may be either stalked ...
Darwin, 1854 *** Order Pedunculata
Lamarck Jean-Baptiste Pierre Antoine de Monet, chevalier de Lamarck (1 August 1744 – 18 December 1829), often known simply as Lamarck (; ), was a French naturalist, biologist, academic, and soldier. He was an early proponent of the idea that biolog ...
, 1818
*** Order
Sessilia Sessilia is an unranked clade of barnacles, comprising the barnacles without stalks, or acorn barnacles. They form a monophyletic group and are probably derived from stalked or goose barnacles. Sessilia is divided into two orders. The Verrucomo ...
Lamarck, 1818 In 2021, Chan et al. elevated Cirripedia to subclass of the class
Thecostraca Thecostraca is a class of marine invertebrates containing over 2,200 described species. Many species have planktonic larvae which become sessile or parasitic as adults. The most important subgroup are the barnacles (subclass Cirripedia), constit ...
, and the superorders Acrothoracica, Rhizocephala, and Thoracica to infraclass. The updated classification, which now includes 11 orders, has been accepted in the World Register of Marine Species. * Subclass Cirripedia Burmeister, 1834 ** Infraclass
Acrothoracica The Acrothoracica are an infraclass of barnacles. Acrothoracicans bore into calcareous material such as mollusc shells, coral, crinoids or hardgrounds, producing a slit-like hole in the surface known by the trace fossil name ''Rogerella''. Acr ...
Gruvel, 1905 *** Order
Cryptophialida Cryptophialidae is a family of Acrothoracica The Acrothoracica are an infraclass of barnacles. Acrothoracicans bore into calcareous material such as mollusc shells, coral, crinoids or hardgrounds, producing a slit-like hole in the surface k ...
Kolbasov, Newman & Hoeg, 2009 *** Order
Lithoglyptida Lithoglyptida is an order of barnacles in the class Thecostraca. There are 2 families and more than 40 described species in Lithoglyptida. Taxonomy These families, subfamilies, and genera belong to the order Lithoglyptida: : Family Lithoglyptidae ...
Kolbasov, Newman & Hoeg, 2009 ** Infraclass
Rhizocephala Rhizocephala are derived barnacles that parasitise mostly decapod crustaceans, but can also infest Peracarida, mantis shrimps and thoracican barnacles, and are found from the deep ocean to freshwater. Together with their sister groups Thoracica ...
Müller, 1862 ** Infraclass
Thoracica Thoracica is an infraclass of crustaceans which contains the most familiar species of barnacles found on rocky coasts, such as '' Semibalanus balanoides'' and ''Chthamalus stellatus''. They have six well-developed limbs, and may be either stalked ...
Darwin, 1854 *** Superorder Phosphatothoracica Gale, 2019 **** Order
Iblomorpha Iblomorpha is a small order of barnacles in the class Thecostraca. There are only two families and about eight described species in Iblomorpha. Genera These families, subfamilies, and genera belong to the order Iblomorpha: * Order Iblomorpha Bu ...
Buckeridge & Newman, 2006 **** Order †
Eolepadomorpha Eolepadomorpha is an extinct order of barnacles in the class Thecostraca Thecostraca is a class of marine invertebrates containing over 2,200 described species. Many species have planktonic larvae which become sessile or parasitic as adults. T ...
Chan et al., 2021 *** Superorder Thoracicalcarea Gale, 2015 **** Order
Calanticomorpha Calanticomorpha is an order of acorn barnacles in the class Thecostraca. There are 3 families and more than 90 described species in Calanticomorpha. Families These families and genera belong to the order Calanticomorpha: : Order Calanticomorpha C ...
Chan et al., 2021 **** Order
Pollicipedomorpha Pollicipedomorpha is an order of pedunculated barnacles in the class Thecostraca. There are 3 families and more than 30 described species in Pollicipedomorpha. Families These families and genera belong to the order Pollicipedomorpha: : Order Poll ...
Chan et al., 2021 **** Order
Scalpellomorpha Scalpellomorpha is an order of acorn barnacles in the class Thecostraca. There are about 11 families in 3 superfamilies and more than 450 described species in Scalpellomorpha. Families : Order Scalpellomorpha Buckeridge & Newman, 2006 :: Superfam ...
Buckeridge & Newman, 2006 **** Order †
Archaeolepadomorpha Archaeolepadomorpha is an extinct order of barnacles in the class Thecostraca Thecostraca is a class of marine invertebrates containing over 2,200 described species. Many species have planktonic larvae which become sessile or parasitic as adult ...
Chan et al., 2021 **** Order †
Brachylepadomorpha Brachylepadidae is an extinct family of barnacles in the order Brachylepadomorpha, the sole family in the order. There are about 7 genera and more than 20 described species in Brachylepadidae. Genera These genera belong to the family Brachylepad ...
Withers, 1923 **** (Unranked)
Sessilia Sessilia is an unranked clade of barnacles, comprising the barnacles without stalks, or acorn barnacles. They form a monophyletic group and are probably derived from stalked or goose barnacles. Sessilia is divided into two orders. The Verrucomo ...
***** Order
Balanomorpha The Balanomorpha are an order of barnacles, containing familiar acorn barnacles of the seashore. The order contains these families: * Austrobalanidae Newman & Ross, 1976 * Balanidae Leach, 1817 (acorn barnacles) * Bathylasmatidae Newman & Ross ...
Pilsbry, 1916 ***** Order
Verrucomorpha Verrucomorpha is an order of asymmetrical sessile barnacles in the class Thecostraca. They are typically found in deeper and deep-sea habitats. There are 2 families and more than 100 described species in Verrucomorpha. Families These families be ...
Pilsbry, 1916


Fossil record

The oldest definitive fossil barnacle is '' Praelepas'' from the mid-
Carboniferous The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period million years ago ( Mya), to the beginning of the Permian Period, million years ago. The name ''Carbonifero ...
, around 330-320 million years ago. Older claimed barnacles such as ''
Priscansermarinus ''Priscansermarinus barnetti'' is an organism known from the Middle Cambrian Burgess Shale which was originally interpreted as a species of lepadomorph barnacle. Four specimens of ''P. barnetti'' are known from the Greater Phyllopod bed. A reflec ...
'' from the
Middle Cambrian Middle or The Middle may refer to: * Centre (geometry), the point equally distant from the outer limits. Places * Middle (sheading), a subdivision of the Isle of Man * Middle Bay (disambiguation) * Middle Brook (disambiguation) * Middle Creek (di ...
(on the order of ) In A. J. Southward (ed.), 1987. do not show clear barnacle morphological traits. Barnacles first radiated and became diverse during the Late
Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of th ...
. Barnacles underwent a second, much larger radiation beginning during the
Neogene The Neogene ( ), informally Upper Tertiary or Late Tertiary, is a geologic period and system that spans 20.45 million years from the end of the Paleogene Period million years ago ( Mya) to the beginning of the present Quaternary Period Mya. ...
(last 23 million years), which continues to present. In part, their poor skeletal preservation is due to their restriction to high-energy environments, which tend to be
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is distin ...
al – therefore it is more common for their shells to be ground up by wave action than for them to reach a depositional setting. Barnacles can play an important role in estimating paleo-water depths. The degree of disarticulation of fossils suggests the distance they have been transported, and since many species have narrow ranges of water depths, it can be assumed that the animals lived in shallow water and broke up as they were washed down-slope. The completeness of fossils, and nature of damage, can thus be used to constrain the tectonic history of regions. File:Balanus improvisus on Mya arenaria shell.jpg, ''
Balanus improvisus ''Amphibalanus improvisus'', the bay barnacle, European acorn barnacle, is a species of Sessilia, acorn barnacle in the Family (biology), family Balanidae. Description ''Amphibalanus improvisus'' has a smooth white or pale grey conical calcareou ...
'', one of the many barnacle taxa described by
Charles Darwin Charles Robert Darwin ( ; 12 February 1809 – 19 April 1882) was an English naturalist, geologist, and biologist, widely known for his contributions to evolutionary biology. His proposition that all species of life have descended fr ...
File:Megabalanus on breccia.JPG,
Miocene The Miocene ( ) is the first geological epoch of the Neogene Period and extends from about (Ma). The Miocene was named by Scottish geologist Charles Lyell; the name comes from the Greek words (', "less") and (', "new") and means "less recen ...
(
Messinian The Messinian is in the geologic timescale the last age or uppermost stage of the Miocene. It spans the time between 7.246 ± 0.005 Ma and 5.333 ± 0.005 Ma (million years ago). It follows the Tortonian and is followed by the Zanclean, the first ...
) ''
Megabalanus ''Megabalanus'' is a genus of barnacles in the family Balanidae. Members of the genus grow to in length and inhabit the lower intertidal zone. Morphology ''Megabalanus'' is an acorn barnacle, a sessile crustacean that secretes a calcium carbon ...
'', smothered by sand and fossilised File:Chesaconcavus top view.jpg, ''Chesaconcavus'', a Miocene barnacle from Maryland


Relationship with humans

Barnacles are of economic consequence, as they often attach themselves to synthetic structures, sometimes to the structure's detriment. Particularly in the case of ships, they are classified as
fouling Fouling is the accumulation of unwanted material on solid surfaces. The fouling materials can consist of either living organisms (biofouling) or a non-living substance (inorganic or organic). Fouling is usually distinguished from other surf ...
organisms. The number and size of barnacles that cover ships can impair their efficiency by causing
hydrodynamic In physics and engineering, fluid dynamics is a subdiscipline of fluid mechanics that describes the flow of fluids—liquids and gases. It has several subdisciplines, including ''aerodynamics'' (the study of air and other gases in motion) and ...
drag. This is not a problem for boats on inland waterways, as barnacles are exclusively marine. The stable
isotope Isotopes are two or more types of atoms that have the same atomic number (number of protons in their nuclei) and position in the periodic table (and hence belong to the same chemical element), and that differ in nucleon numbers (mass numbers) ...
signals in the layers of barnacle shells can potentially be used as a forensic tracking method for
whale Whales are a widely distributed and diverse group of fully aquatic placental marine mammals. As an informal and colloquial grouping, they correspond to large members of the infraorder Cetacea, i.e. all cetaceans apart from dolphins and ...
s,
loggerhead turtle The loggerhead sea turtle (''Caretta caretta'') is a species of oceanic turtle distributed throughout the world. It is a marine reptile, belonging to the family Cheloniidae. The average loggerhead measures around in carapace length when full ...
s and
marine debris Marine debris, also known as marine litter, is human-created waste that has deliberately or accidentally been released in a sea or ocean. Floating oceanic debris tends to accumulate at the center of gyres and on coastlines, frequently washing ...
, such as
shipwreck A shipwreck is the wreckage of a ship that is located either beached on land or sunken to the bottom of a body of water. Shipwrecking may be intentional or unintentional. Angela Croome reported in January 1999 that there were approximately ...
s or a
flaperon A flaperon (a portmanteau of flap and aileron) on an aircraft's wing is a type of control surface that combines the functions of both flaps and ailerons. Some smaller kitplanes have flaperons for reasons of simplicity of manufacture, while s ...
suspected to be from
Malaysia Airlines Flight 370 Malaysia Airlines Flight 370 (MH370/MAS370) was an international passenger flight operated by Malaysia Airlines that disappeared on 8 March 2014 while flying from Kuala Lumpur International Airport in Malaysia to its planned destination ...
. The flesh of some barnacles is routinely consumed by humans, including Japanese goose barnacles (''e.g.'' '' Capitulum mitella''), and
goose barnacle Goose barnacles, also called stalked barnacles or gooseneck barnacles, are filter-feeding crustaceans that live attached to hard surfaces of rocks and flotsam in the ocean intertidal zone. Goose barnacles formerly made up the taxonomic order Ped ...
s (''e.g.'' ''
Pollicipes pollicipes ''Pollicipes pollicipes'', known as the goose neck barnacle, goose barnacle or leaf barnacle is a species of goose barnacle, also well known under the taxonomic synonym ''Pollicipes cornucopia''. It is closely related to '' Pollicipes polymerus'' ...
''), a delicacy in
Spain , image_flag = Bandera de España.svg , image_coat = Escudo de España (mazonado).svg , national_motto = ''Plus ultra'' (Latin)(English: "Further Beyond") , national_anthem = (English: "Royal March") , i ...
and
Portugal Portugal, officially the Portuguese Republic ( pt, República Portuguesa, links=yes ), is a country whose mainland is located on the Iberian Peninsula of Southwestern Europe, and whose territory also includes the Atlantic archipelagos of ...
. The resemblance of this barnacle's fleshy stalk to a goose's neck gave rise, in ancient times, to the notion that geese literally grew from the barnacle. Indeed, the word "barnacle" originally referred to a species of goose, the
barnacle goose The barnacle goose (''Branta leucopsis'') is a species of goose that belongs to the genus '' Branta'' of black geese, which contains species with largely black plumage, distinguishing them from the grey ''Anser'' species. Despite its superficial ...
''Branta leucopsis'', whose eggs and young were rarely seen by humans because it breeds in the remote
Arctic The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...
. Additionally, the picoroco barnacle is used in
Chilean cuisine Chilean cuisine stems mainly from the combination of traditional Spanish cuisine, Chilean Mapuche culture and local ingredients, with later important influences from other European cuisines, particularly from Germany, the United Kingdom and Fr ...
and is one of the ingredients in ''
curanto Curanto (from arn, kurantu 'stony') is a traditional Chilote method of cooking food using heated rocks buried in a earth oven that is covered with pangue leaves and turf. The fundamental components are seafood, potatoes, along with other traditi ...
'' seafood stew.
MIT The Massachusetts Institute of Technology (MIT) is a private land-grant research university in Cambridge, Massachusetts. Established in 1861, MIT has played a key role in the development of modern technology and science, and is one of the mo ...
researchers developed an adhesive, inspired by a protein-based bioglue produced by barnacles to firmly attach to rocks, which can form a tight seal to halt
bleeding Bleeding, hemorrhage, haemorrhage or blood loss, is blood escaping from the circulatory system from damaged blood vessels. Bleeding can occur internally, or externally either through a natural opening such as the mouth, nose, ear, urethra, vag ...
within about 15 seconds of application. File:Siuslaw River-1.jpg, Barnacles attached to pilings along the
Siuslaw River The Siuslaw River ( ) is a river, about long, that flows to the Pacific Ocean coast of Oregon in the United States. It drains an area of about in the Central Oregon Coast Range southwest of the Willamette Valley and north of the watershed of t ...
in
Oregon Oregon () is a U.S. state, state in the Pacific Northwest region of the Western United States. The Columbia River delineates much of Oregon's northern boundary with Washington (state), Washington, while the Snake River delineates much of it ...
File:Percebes.iguaria.jpg,
Goose barnacle Goose barnacles, also called stalked barnacles or gooseneck barnacles, are filter-feeding crustaceans that live attached to hard surfaces of rocks and flotsam in the ocean intertidal zone. Goose barnacles formerly made up the taxonomic order Ped ...
s in a restaurant in
Madrid Madrid ( , ) is the capital and most populous city of Spain. The city has almost 3.4 million inhabitants and a metropolitan area population of approximately 6.7 million. It is the second-largest city in the European Union (EU), and ...


See also

*
List of Cirripedia genera These genera belong to Cirripedia, a subclass of barnacles in the phylum of Crustacea, as classified by Chan et al. (2021) and the World Register of Marine Species. Their classification into order, superfamily, family, and subfamily is included. ...


References


Further reading

*


External links


Barnacles
from the Marine Education Society of Australasia

Article on barnacles in Spain, and their collection and gastronomy. * * * * {{Authority control Parasitic crustaceans Maxillopoda Articles containing video clips Extant Cambrian first appearances