51-513: Rhizocephala are derived barnacles that are parasitic castrators . Their hosts are mostly decapod crustaceans , but include Peracarida , mantis shrimps and thoracican barnacles. Their habitats range from the deep ocean to freshwater. Together with their sister groups Thoracica and Acrothoracica , they make up the subclass Cirripedia . Their body plan is uniquely reduced in an extreme adaptation to their parasitic lifestyle, and makes their relationship to other barnacles unrecognisable in
102-428: 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
153-463: A few fungi, a few species of trematodes , and a parasitic castrator isopod , Hemioniscus balani . 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
204-436: A forensic tracking method for whales , loggerhead turtles and for marine debris , such as shipwrecks or aircraft wreckage. Sylon hippolytes Sylon hippolytes is a castrating parasite that infects the shrimp Pandalina brevirostris . The adult female parasite consists of a body that can be differentiated into two distinct regions: a sac-like structure containing the reproductive organs (the externa), and
255-430: A quarter of individuals with a close neighbour. This 2013 discovery overturned the long-held belief that barnacles were limited to pseucocopulation or hermaphroditism. Rhizocephalan barnacles had been considered hermaphroditic, but their males inject themselves into females' bodies, degrading to little more than sperm-producing cells. Most barnacles are filter feeders. From within their shell, they repeatedly reach into
306-428: 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. Other members of the class have an entirely different mode of life. Barnacles of
357-483: A retractive hollow stylet on the larva's head. The kentrogon stage seems to have been secondarily lost in all of the Akentrogonida, where the cypris injects the vermigon through one of its antennules. The vermigon grows into a network of root-like threads through the host's tissue, centering on the digestive system and especially the hepatopancreas , and absorb nutrients from the hemolymph. The network of threads
408-401: A sinus close to the esophagus 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 gills , absorbing oxygen from the water through the cirri and the surface of the body. The excretory organs of barnacles are maxillary glands. The main sense of barnacles appears to be touch, with the hairs on
459-404: 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. As the larva exhausts its energy reserves, it becomes less selective in
510-442: A trophic, root like system situated inside the hosts body (the interna). It forms an elongated, sac-like growth on the abdomen of several shrimp species, measuring up to 1.2 centimeters in diameter. S. hippolytes castrates infected female shrimp by absorbing the reproductive energy of the host. Many other Rhizocephalan have the same castrating characteristic. The presence of the parasite will eventually come to pass after it dies, and
561-589: Is Praelepas from the mid- Carboniferous , around 330-320 million years ago. Older claimed barnacles such as Priscansermarinus from the Middle Cambrian , some 510 to 500 million years ago , 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
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#1732790140513612-405: Is called the interna. The female then grows a sac-like externa, which consists of a mantle, a mantle cavity, an ovary and a pair of passageways known as cell receptacles, extruding from the abdomen of the host. In the order Kentrogonida, the virgin externa contains no openings at first. But it soon molts to a second stage that contains an orifice known as the mantle departure, and which leads into
663-488: Is fished, or overfished, in commercial quantities on the Chilean coast, where it is known as the picoroco . 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. The stable isotope signals in the layers of barnacle shells can potentially be used as
714-409: 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 . 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
765-426: Is the homologue of the female kentrogon, but is reduced to an amoeboid unsegmented cuticle-covered mass of cells consisting of three to four cell-types: the dorsolateral, the ventral epidermis, the inclusion cells, and the postganglion. The externa have room for two males, one for each of the receptacles, which increase the heterozygosity of the offspring. Once inside, the trichogen will shed its cuticle before reaching
816-480: Is the rule in Kentrogonida, the number of implanted males in Akentrogonida can range from just one to more than ten. The small cluster of cells injected by the male cypris differentiates into a loosely connected mass of sperm-producing germ cells, once it reaches its destination inside the female. Being nothing more than sperm-forming cells, these adult male rhizocephalans represent the simplest form of male in
867-422: Is where the host's egg sac would be, and the host's behaviour is chemically altered: it is castrated and does not moult until the aged externa drops off. The host treats the externa as if it were its own egg sac. This behaviour even extends to male hosts, which would never have carried eggs, but care for the externa in the same way as females. Following an updated classification of barnacles by Chan et al. (2021),
918-531: The Mollusca to Articulata (in modern terms, annelids + arthropods), showing naturalists that detailed study was needed to reevaluate their taxonomy. 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
969-609: The barnacle goose . 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. The name Cirripedia comes from the Latin words cirritus "curly" from cirrus "curl" and pedis from pes "foot". The two words together mean "curly-footed", alluding to
1020-579: The mussel Mytilus edulis and the ascidian Styela gibbsi . Another predator is the starfish species Pisaster ochraceus . 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. 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),
1071-465: 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 . All but
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#17327901405131122-508: The nervous system . Females have a cuticle , which is never shed. Other than the minute larval stages, there is nothing identifying them as crustaceans or even arthropods in general. The only distinguishable portion of a rhizocephalan body is the externa: the reproductive portion of adult females. Nauplii released from adult females swim in water for several days without taking food (the larva has no mouth and no intestine) and transform into cypris larvae ( cyprids ) after several moults . Like
1173-556: 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
1224-598: 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. Barnacles are displaced by limpets and mussels , which compete for space. They employ two strategies to overwhelm their competitors: "swamping", and fast growth. In
1275-715: 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: 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 . Barnacles are of economic consequence, as they often attach themselves to man-made structures. Particularly in
1326-681: The Late Cretaceous . Barnacles underwent a second, much larger radiation beginning during the Neogene and still continuing. The following cladogram , not fully resolved, shows the phylogenetic relationships of the Cirripedia within Thecostraca as of 2021. Facetotecta Laurida Dendrogastrida Cryptophialida Lithoglyptida Iblomorpha Pollicipedomorpha Calanticomorpha Scalpellomorpha Verrucomorpha Balanomorpha Rhizocephala Over 2,100 species of Cirripedia have been described. Some authorities regard
1377-464: The adult form. The name Rhizocephala derives from the Ancient Greek roots ῥίζα ( rhiza , "root") and κεφαλή ( kephalē , "head"), describing the adult female, which mostly consists of a network of thread-like extensions penetrating the body of the host. Adult rhizocephalans lack appendages , segmentation , and all internal organs except gonads , a few muscles, and the remains of
1428-406: The akentrogonids, the kentrogonids have kept their nauplius stage). In species like Clistosaccus paguri , the male injects its cluster of cells which migrates through the connective tissue of the mantle and into the receptacle. But in forms like Sylon hippolytes the receptacle is absent, and the males cells implant in the ovary instead. While only a single male can settle in each receptacle, which
1479-583: 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 acorn barnacles makes sexual reproduction difficult, as they cannot leave their shells to mate. To facilitate genetic transfer between isolated individuals, barnacles have extraordinarily long penises . Barnacles probably have
1530-510: 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 . 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 ), a delicacy in Spain and Portugal . The Chilean giant barnacle Austromegabalanus psittacus
1581-408: The castrating mechanism is reversed for the host. Sylon hippolytes typically lives up to a maximum of one year. Sylon hippolytes are r-strategists. An externa can only produce offspring once during its lifetime. Therefore, the parasite utilizes an enormous amount of energy towards producing as many eggs as possible for reproduction. The size of the parasitic sac has proportional relationship with
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1632-409: 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,
1683-468: 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 . This natural cement can withstand a pulling strength of 5,000 lbf/in (30,000 kPa) and a sticking strength of 22–60 lbf/in (200–400 kPa). Barnacles have no true heart , although
1734-487: 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 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
1785-407: The curved legs used in filter-feeding. 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. Barnacles have
1836-465: The end of the passageway. In the order Akentrogonida, which form a monophyletic group nested within the paraphyletic Kentrogonida, the male does not develop into a trichogon, and the cypris injects its cell mass through its antennule and directly into the body of the immature externa. The offspring also hatch directly into fully developed cyprids instead of nauplius larvae (except for a few species of kentrogonid rhizocephalans, which hatch into cyprids like
1887-401: The entire animal kingdom. Mature female externa releases eggs into its mantle cavity where eggs are fertilised by sperm from the hyper-parasitic male(s). Due to the larval sexual dimorphism in the Kentrogonida, the females produce two different egg sizes; small female eggs and larger male eggs. It appears the sex determination in Akentrogonida is environmental. In Peltogasterella gracilis ,
1938-444: 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. Their hard shells are assumed by zoologists to have evolved as an anti-predator adaptation . One group of stalked barnacles has adapted to
1989-460: The externa produces several batches of larvae before it drops off the host, taking the male(s) inside with it. After the original externa disappear, the host moults and the interna grows buds that each develops into a new virgin externa. The females commonly has two cypris cell receptacles. With more than one externa, and new ones replacing the old ones, each female Peltogasterella can receive sperm from numerous males during her lifetime. The externa
2040-490: The first instars are filter feeders. 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. 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
2091-451: The generalisations needed for his theory of evolution by natural selection . 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?'" Upon the conclusion of his research, Darwin declared "I hate a barnacle as no man ever did before." The oldest definitive fossil barnacle
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2142-485: The internal relationships of Rhizocephala as of 2020, as well as the number of species in each family. The tree is not fully resolved. Triangulidae (4) Mycetomorphidae (2) Peltogastridae (47) Peltogasterellidae (10) Polyascidae (8) Clistosaccidae (2) Polysaccidae (2) Thompsoniidae (24) Pirusaccidae (1) Duplorbidae (5) Chthamalophilidae (4) Parthenopeidae (3) Sacculinidae (177) Barnacle Barnacles are arthropods of
2193-482: The largest penis-to-body size ratio of the animal kingdom, up to eight times their body length, though on exposed coasts the penis is shorter and thicker. The mating of acorn barnacles is described as pseudocopulation. 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
2244-480: 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. The photoreceptors are likely only capable of sensing the difference between light and dark. This eye is derived from the primary naupliar eye . Barnacles pass through two distinct larval stages,
2295-593: 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. 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
2346-407: The nauplii, the cyprids are lecithotrophic (non-feeding). The female cypris larva in Kentrogonida settles on a host and metamorphoses into a specialized juvenile form, a kentrogon. This has no visible segmentation and no appendages except the antennules . These are used to attach the larva to the host; their only purpose is to inject a cell mass, the vermigon , into the host's hemolymph through
2397-407: The sites it selects. It cements itself permanently to the substrate with another proteinaceous compound, and then undergoes metamorphosis into a juvenile barnacle. 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
2448-455: The subgroups Akentrogonida and Kentrogonida were dropped, leaving 13 families as children of the infraclass Rhizocephala. The Rhizocephala have not so far been found as fossils. The following cladogram shows the phylogenetic relationships of the Cirripedia within Thecostraca as of 2021. Facetotecta Ascothoracida Acrothoracica Thoracica (stalked and acorn barnacles) Rhizocephala The following cladogram summarizes
2499-543: 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 7 cm (3 in) in length. Competitors may include other barnacles. Balanoids gained their advantage over
2550-400: The two receptacle passageways — once assumed to be the testes in hermaphroditic parasites before the realization that they were actually two separate sexes — and starts releasing pheromones to attract male cyprids. From inside the body of the male cypris that succeeds in entering the departure, a unique and very short lived male stage called the trichogen emerges through the antennule opening. It
2601-498: The water column with their cirri. These feathery appendages beat rhythmically to draw plankton and detritus into the shell for consumption. Although they have been found at water depths to 600 m (2,000 ft), most barnacles inhabit shallow waters, with 75% of species living in water depths less than 100 m (300 ft), and 25% inhabiting the intertidal zone . Within the intertidal zone, different species of barnacles live in very tightly constrained locations, allowing
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