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 independently from different ancestral gastropods. This general category of conical shell is known as "patelliform" (dish-shaped).All members of the large and ancient marine clade Patellogastropoda are limpets. Within that clade, the members of the Patellidae family in particular are often referred to as "true limpets".
Other groups, not in the same family, are also called limpets of one type or another, due to the similarity of their shells' shape. Examples include the Fissurellidae ("keyhole limpet") family, which is part of the Vetigastropoda clade (many other members of the Vetigastropoda do not have the morphology of limpets) and the Siphonariidae ("false limpets"), which use a siphon to pump water over their gills.
Some species of limpet live in fresh water,but these are the exception.
Many species of limpets have historically been used, or are still used, by humans and other animals for food.
The basic anatomy of a limpet consists of the usual molluscan organs and systems:
The two kidneys are very different in size and location. This is a result of torsion. The left kidney is diminutive and in most limpets is barely functional. The right kidney, however, has taken over the majority of blood filtration and often extends over and around the entire mantle of the animal in a thin, almost-invisible layer.
True limpets in the family Patellidae live on hard surfaces in the intertidal zone. Unlike barnacles (which are not molluscs but may resemble limpets in appearance) or mussels (which are bivalve molluscs that cement themselves to a substrate for their entire adult lives), limpets are capable of locomotion instead of being permanently attached to a single spot. However, when they need to resist strong wave action or other disturbances, limpets cling extremely firmly to the surfaces on which they live, using their muscular foot to apply suction combined with the effect of adhesive mucus. It often is very difficult to remove a true limpet from a rock without injuring or killing it.
All "true" limpets are marine. The most primitive group have one pair of gills, in others only a single gill remains, the lepetids don't have any gills at all, while the patellids have evolved secondary gills as they have lost the original pair.However, because the adaptive feature of a simple conical shell has repeatedly arisen independently in gastropod evolution, limpets from many different evolutionary lineages occur in widely different environments. Some saltwater limpets such as Trimusculidae breathe air, and some freshwater limpets are descendants of air-breathing land snails (e.g. the genus Ancylus ) whose ancestors had a pallial cavity serving as a lung. In these small freshwater limpets, that "lung" underwent secondary adaptation to allow the absorption of dissolved oxygen from water.
The common name "limpet" also is applied to a number of not very closely related groups of sea snails and freshwater snails (aquatic gastropod mollusks). Thus the common name "limpet" has very little taxonomic significance in and of itself; the name is applied not only to true limpets (the Patellogastropoda), but also to all snails that have a simple shell that is broadly conical in shape, and either is not spirally coiled, or appears not to be coiled in the adult snail. In other words, the shell of all limpets is "patelliform", which means the shell is shaped more or less like the shell of most true limpets. The term "false limpets" is used for some (but not all) of these other groups that have a conical shell.
Thus, the name limpet is used to describe various extremely diverse groups of gastropods that have independently evolved a shell of the same basic shape (see convergent evolution). And although the name "limpet" is given on the basis of a limpet-like or "patelliform" shell, the several groups of snails that have a shell of this type are not at all closely related to one another.
In order to obtain food, limpets rely on an organ called the radula, which contains iron-mineralized teeth.Although limpets contain over 100 rows of teeth, only the outermost 10 are used in feeding. These teeth form via matrix-mediated biomineralization, a cyclic process involving the delivery of iron minerals to reinforce a polymeric chitin matrix. Upon being fully mineralized, the teeth reposition themselves within the radula, allowing limpets to scrape off algae from rock surfaces. As limpet teeth wear out, they are subsequently degraded (occurring anywhere between 12 and 48 hours) and replaced with new teeth. Different limpet species exhibit different overall shapes of their teeth.
Development of limpet teeth occurs in conveyor belt style, where teeth start growing at the back of the radula, and move toward the front of this structure as they mature.The growth rate of the limpet's teeth is around 47 hours per row. Fully mature teeth are located in the scraping zone, the very front of the radula. The scraping zone is in contact with the substrate that the limpet feeds off of. As a result, the fully mature teeth are subsequently worn down until they are discarded – at a rate equal to the growth rate. To counter this degradation, a new row of teeth begin to grow.
Currently, the exact mechanism behind the biomineralization of limpet teeth is unknown. However, it is suggested that limpet teeth biomineralize using a dissolution-reprecipitation mechanism.Specifically, this mechanism is associated with the dissolution of iron stored in epithelial cells of the radula to create ferrihydrite ions. These ferrihydrite ions are transported through ion channels to the tooth surface. The build-up of enough ferrihydrite ions leads to nucleation, the rate of which can be altered via changing the pH at the site of nucleation. After one to two days, these ions are converted to goethite crystals.
The unmineralized matrix consists of relatively well-ordered, densely packed arrays of chitin fibers, with only a few nanometers between adjacent fibers.The lack of space leads to the absence of pre-formed compartments within the matrix that control goethite crystal size and shape. Because of this, the main factor influencing goethite crystal growth is the chitin fibers of the matrix. Specifically, goethite crystals nucleate on these chitin fibers and push aside or engulf the chitin fibers as they grow, influencing their resulting orientation.
Looking into limpet teeth of Patella vulgata , Vickers hardness values are between 268 and 646 kg⋅m−1⋅s−2, while tensile strength values range between 3.0 and 6.5 GPa. As spider silk has a tensile strength only up to 4.5 GPa, limpet teeth outperforms spider silk to be the strongest biological material. These considerably high values exhibited by limpet teeth are due to the following factors:
The first factor is the nanometer length scale of goethite nanofibers in limpet teeth;at this length scale, materials become insensitive to flaws that would otherwise decrease failure strength. As a result, goethite nanofibers are able to maintain substantial failure strength despite the presence of defects.
The second factor is the small critical fiber length of the goethite fibers in limpet teeth. nm, which is several orders of magnitude away from their estimated fiber length of 3.1 μm. This suggests that the goethite nanofibers serve as effective reinforcement for the collagen matrix and significantly contribute to the load-bearing capabilities of limpet teeth. This is further supported by the large mineral volume fraction of elongated goethite nanofibers within limpet teeth, around 0.81.Critical fiber length is a parameter defining the fiber length that a material must be to transfer stresses from the matrix to the fibers themselves during external loading. Materials with a large critical fiber length (relative to the total fiber length) act as poor reinforcement fibers, meaning that most stresses are still loaded on the matrix. Materials with small critical fiber lengths (relative to the total fiber length) act as effective reinforcement fibers that are able to transfer stresses on the matrix to themselves. Goethite nanofibers express a critical fiber length of around 420 to 800
Applications of limpet teeth involve structural designs requiring high strength and hardness, such as biomaterials used in next-generation dental restorations.
The structure, composition, and morphological shape of the teeth of the limpet allow for an even distribution of stress throughout the tooth.The teeth have a self-sharpening mechanism which allows for the teeth to be more highly functional for longer periods of time. Stress wears preferentially on the front surface of the cusp of the teeth, allowing the back surface to stay sharp and more effective.
There is evidence that different regions of the limpet teeth show different mechanical strengths.Measurements taken from the tip of the anterior edge of the tooth show that the teeth can exhibit an elastic modulus of around 140 GPa. Traveling down the anterior edge toward the anterior cusp of the teeth however, the elastic modulus decreases ending around 50 GPa at the edge of the teeth. The orientation of the goethite fibers can be correlated to this decrease in elastic modulus, as towards the tip of the tooth the fibers are more aligned with each other, correlating to a high modulus and vice versa.
Critical length of the goethite fibers is the reason the structural chitin matrix has extreme support. The critical length of goethite fibers has been estimated to be around 420 to 800 nm and when compared with the actual length of the fibers found in the teeth, around 3.1 um, shows that the teeth have fibers much larger than the critical length. This paired with orientation of the fibers leads to effective stress distribution onto the goethite fibers and not onto the weaker chitin matrix in the limpet teeth.
The overall structure of the limpet teeth is relatively stable within most natural conditions given the limpet's ability to produce new teeth at a similar rate to the degradation.Individual teeth are subjected to shear stresses as the tooth is dragged along the rock. Goethite as a mineral is a relatively soft iron based material, which increases the chance of physical damage to the structure. Limpet teeth and the radula have also been shown to experience greater levels of damage in CO2 acidified water.
Goethite crystals form in at the start of the tooth production cycle and remain as a fundamental part of the tooth with intercrystal space filled with amorphous silica. Existing in multiple morphologies, “Prisms with rhomb-shaped sections are the most frequent...”.The goethite crystals are stable and well formed for a biogenic crystal. The transport of the mineral to create the crystal structures has been suggested to be a dissolution-reprecipitation mechanism as of 2011. Limpet tooth structure is dependent upon living depth of the specimen. While deep water limpets have been shown to have the same elemental composition as shallow water limpets, deep water limpets do not show crystalline phases of goethite.
The initial event that takes place when the limpet creates a new row of teeth is the creation of the main macromolecular α-chitin component. The resulting organic matrix serves as framework for the crystallization of the teeth themselves.The first mineral to be deposited is goethite (α-FeOOH), a soft iron oxide which forms crystals parallel to the chitin fibers. The goethite, however, has varying different crystal habits. The crystals arrange in various shapes and even thicknesses throughout the chitin matrix. Still, depending on the formation of the chitin matrix, this can have varying profound effects on the formation of the goethite crystals. The space in between the crystals and the chitin matrix is filled with an amorphous hydrated silica (SiO2).
The most prominent metal by percent composition is iron in the form of goethite. Goethite has the chemical formula of FeO(OH) and belongs to a group known as oxy-hydroxides. There exists amorphous silica between the goethite crystals; surrounding the goethite is a matrix of chitin.Chitin has a chemical formula of C8H13O5N. Other metals have been shown to be present with the relative percent compositions varying on geographic locations. The goethite has been reported to have a volume fraction of approximately 80%.
Limpets from different locations were shown to have different elemental ratios within their teeth. Iron is consistently most abundant however other metals such as sodium, potassium, calcium, and copper were all shown to be present to varying degrees.The relative percentages of the elements have also been shown to differ from one geographic location to another. This demonstrates an environmental dependency of some kind; however the specific variables are currently undetermined.
Gastropods that have limpet-like or patelliform shells are found in several different clades:
Most marine limpets have gills, whereas all freshwater limpets and a few marine limpets have a mantle cavity adapted to breathe air and function as a lung (and in some cases again adapted to absorb oxygen from water). All these kinds of snail are only very distantly related.
Limpet mines are a type of naval mine attached to a target by magnets. They are named after the tenacious grip of the limpet.
The humorous author Edward Lear wrote "Cheer up, as the limpet said to the weeping willow" in one of his letters.Simon Grindle wrote the 1964 illustrated children's book of nonsense poetry The Loving Limpet and Other Peculiarities, said to be "in the great tradition of Edward Lear and Lewis Carroll".
In his book South , Sir Ernest Shackleton relates the stories of his twenty-two men left behind on Elephant Island harvesting limpets from the icy waters on the shore of the Southern Ocean. Near the end of their four-month stay on the island, as their stocks of seal and penguin meat dwindled, they derived a major portion of their sustenance from limpets.
The light-hearted comedy movie The Incredible Mr. Limpet is about a patriotic but weak American who desperately clings to the idea of joining the U.S. military to serve his country; by the end of the movie, having been transformed into a fish, he is able to use his new body to save U.S. naval vessels from disaster. Although he does not become a snail but a fish, his name limpet hints at his tenacity.
Goethite is a mineral of the diaspore group, consisting of iron(III) oxide-hydroxide, specifically the "α" polymorph. It is found in soil and other low-temperature environments such as sediment. Goethite has been well known since ancient times for its use as a pigment. Evidence has been found of its use in paint pigment samples taken from the caves of Lascaux in France. It was first described in 1806 based on samples found in the Hollertszug Mine in Herdorf, Germany. The mineral was named after the German polymath and poet Johann Wolfgang von Goethe (1749–1832).
The radula is an anatomical structure used by mollusks for feeding, sometimes compared to a tongue. It is a minutely toothed, chitinous ribbon, which is typically used for scraping or cutting food before the food enters the esophagus. The radula is unique to the molluscs, and is found in every class of mollusc except the bivalves, which instead use cilia, waving filaments that bring minute organisms to the mouth.
Chitons are marine molluscs of varying size in the class Polyplacophora, formerly known as Amphineura. About 940 extant and 430 fossil species are recognized.
Biomineralization, also written biomineralisation, is the process by which living organisms produce minerals, often to harden or stiffen existing tissues. Such tissues are called mineralized tissues. It is an extremely widespread phenomenon; all six taxonomic kingdoms contain members that are able to form minerals, and over 60 different minerals have been identified in organisms. Examples include silicates in algae and diatoms, carbonates in invertebrates, and calcium phosphates and carbonates in vertebrates. These minerals often form structural features such as sea shells and the bone in mammals and birds. Organisms have been producing mineralized skeletons for the past 550 million years. Ca carbonates and Ca phosphates are usually crystalline, but silica organisms (sponges, diatoms...) are always non crystalline minerals. Other examples include copper, iron and gold deposits involving bacteria. Biologically formed minerals often have special uses such as magnetic sensors in magnetotactic bacteria (Fe3O4), gravity-sensing devices (CaCO3, CaSO4, BaSO4) and iron storage and mobilization (Fe2O3•H2O in the protein ferritin).
Natural fibers or natural fibres are fibers that are produced by plants, animals, and geological processes. They can be used as a component of composite materials, where the orientation of fibers impacts the properties. Natural fibers can also be matted into sheets to make paper or felt.
The Patellogastropoda, common name true limpets and historically called the Docoglossa, are members of a major phylogenetic group of marine gastropods, treated by experts either as a clade or as a taxonomic order.
Sea snail is a common name for slow-moving marine gastropod molluscs, usually with visible external shells, such as whelk or abalone. They share the taxonomic class Gastropoda with slugs, which are distinguished from snails primarily by the absence of a visible shell.
Hydrocenidae is a taxonomic family of minute land snails or cave snails with an operculum, terrestrial gastropod mollusks or micromollusks in the clade Cycloneritimorpha.
Latia neritoides is a species of small freshwater snail or limpet, an aquatic gastropod mollusc in the family Latiidae.
Lepetelloidea is a superfamily of sea snails, small deepwater limpets, marine gastropod mollusks in the clade Vetigastropoda.
The molluscshell is typically a calcareous exoskeleton which encloses, supports and protects the soft parts of an animal in the phylum Mollusca, which includes snails, clams, tusk shells, and several other classes. Not all shelled molluscs live in the sea; many live on the land and in freshwater.
Mollusca is the second-largest phylum of invertebrate animals after the Arthropoda. The members are known as molluscs or mollusks. Around 85,000 extant species of molluscs are recognized. The number of fossil species is estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.
Patella vulgata, common name the common limpet or common European limpet is a species of sea snail. It is a typical true limpet; a marine gastropod mollusc in the family Patellidae, with gills. This species occurs in the waters of Western Europe.
Cellana exarata, common name the black-foot ʻopihi and Hawaiian blackfoot is a species of edible true limpet, a marine gastropod mollusc in the family Nacellidae, one of the families of true limpets. ‘Opihi are significant in Hawaiian history where they have had many uses such as food, tools, and jewelry. They are known as a “fish of death.”
The following is a glossary of common English language and scientific terms used in the description of gastropods.
Mineralized tissues are biological tissues that incorporate minerals into soft matrices. Typically these tissues form a protective shield or structural support. Bone, mollusc shells, deep sea sponge Euplectella species, radiolarians, diatoms, antler bone, tendon, cartilage, tooth enamel and dentin are some examples of mineralized tissues.
A tooth is a hard, calcified structure found in the jaws of many vertebrates and used to break down food. Some animals, particularly carnivores, also use teeth for hunting or for defensive purposes. The roots of teeth are covered by gums. Teeth are not made of bone, but rather of multiple tissues of varying density and hardness that originate from the embryonic germ layer, the ectoderm.
Cymbula adansonii is a species of sea snail, a true limpet, a marine gastropod mollusk in the family Patellidae. It is one of the several families of true limpets. Marine gastropods, colloquially classified as snails and slugs, encompass the entire class of invertebrates in the Mollusca phylum. True limpets, are pelagic snails within the Patellidae family.
Nipponacmea is a genus of sea snails, the true limpets, marine gastropod mollusks in the family Lottiidae.
Marine biogenic calcification is the process by which marine organisms such as oysters and clams form calcium carbonate. Seawater is full of dissolved compounds, ions and nutrients that organisms can utilize for energy and, in the case of calcification, to build shells and outer structures. Calcifying organisms in the ocean include molluscs, foraminifera, coccolithophores, crustaceans, echinoderms such as sea urchins, and corals. The shells and skeletons produced from calcification have important functions for the physiology and ecology of the organisms that create them.