Although all limpets are members of the class Gastropoda, limpets are polyphyletic, meaning that the various groups that are called "limpets" have descended independently from different ancestral gastropods. This general category of conical shell is technically known as "patelliform", meaning dish-shaped. Some species of limpet live in fresh water, but these are the exception. All members of the large and ancient marine clade Patellogastropoda are limpets, and within that clade the family Patellidae in particular are often called the "true limpets".
Other groups, not in the same family, are also called limpets of one type or another because of the similar shapes of their shells. Examples include the Fissurellidae, the "keyhole limpet" family, which is part of the clade Vetigastropoda (many other members of the Vetigastropoda do not have the morphology of limpets) and the Siphonariidae, the "false limpets", which use a siphon to pump water over their gills.
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 remain, 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 a conveyor-belt style manner, 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 m−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. 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 nm, which is several orders of magnitude away from their estimated fiber length of 3.1 um. 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.
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".
The following lists events that happened during 1986 in South Africa.1988 in South Africa
The following lists events that happened during 1988 in South Africa.Apex (mollusc)
In anatomy, an apex (adjectival form: apical) is part of the shell of a mollusk. The apex is the pointed tip (the oldest part) of the shell of a gastropod, scaphopod, or cephalopod.
The apex is used in end-blown conches.Calyptraeidae
The Calyptraeidae, the slipper snails or slipper limpets, cup-and-saucer snails, and Chinese hat snails, are a family of small to medium-sized marine prosobranch gastropods. This family includes the slipper snails (Crepidula species), the Chinese hat snails, (Calyptraea species), and the cup-and-saucer snails (Crucibulum species) among others.
The Calyptraeidae are the only family in the superfamily Calyptraeoidea. This family has no subfamilies according to the taxonomy of the Gastropoda by Bouchet & Rocroi, 2005.
Crepidula fornicata was brought to Europe on imported American oysters in the late 19th century and is now considered a significant pest in European oyster beds.Cellana exarata
Cellana exarata, common name the black-foot opihi 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.Cellana talcosa
Cellana talcosa, the talc limpet or turtle limpet is a species of true limpet, a marine gastropod mollusc in the family Nacellidae, which is one of the true limpet families.
This species is endemic to the Hawaiian islands, where its common name is koele or opihi ko'ele.  It is the largest limpet found in the Hawaiian islands and can reach 4 inches in diameter.Common slipper shell
The common slipper shell, (Crepidula fornicata), has many other common names, including common Atlantic slippersnail, boat shell, quarterdeck shell, fornicating slipper snail, Atlantic slipper limpet and it is known in Britain as the "common slipper limpet". This is a species of medium-sized sea snail, a marine gastropod mollusc in the family Calyptraeidae, the slipper snails and cup and saucer snails.Fissurellidae
Fissurellidae, common name the keyhole limpets and slit limpets, is a taxonomic family of limpet-like sea snails, marine gastropod molluscs in the clade Vetigastropoda.
Their common name derives from the small hole in the apex of their cone-like shells. Although superficially resembling "true" limpets, they are in fact not closely related to them.Freshwater snail
Freshwater snails are gastropod mollusks which live in freshwater. There are many different families. They are found throughout the world in various habitats, ranging from ephemeral pools to the largest lakes, and from small seeps and springs to major rivers. The great majority of freshwater gastropods have a shell, with very few exceptions. Some groups of snails that live in freshwater respire using gills, whereas other groups need to reach the surface to breathe air. In addition, some are amphibious and have both gills and a lung (e.g. Ampullariidae). Most feed on algae, but many are detritivors and some are filter feeders.
According to a 2008 review of the taxonomy, there are about 4,000 species of freshwater gastropods (3,795-3,972).At least 33–38 independent lineages of gastropods have successfully colonized freshwater environments. It is not possible to quantify the exact number of these lineages yet, because they have yet to be clarified within the Cerithioidea. From six to eight of these independent lineages occur in North America.Islay LIMPET
Islay LIMPET was the world's first commercial wave power device and was connected to the United Kingdom's National Grid.Limpet mine
A limpet mine is a type of naval mine attached to a target by magnets. It is so named because of its superficial similarity to the limpet, a type of sea snail that clings tightly to rocks or other hard surfaces.
A swimmer or diver may attach the mine, which is usually designed with hollow compartments to give the mine slight negative buoyancy, making it easier to handle underwater.
Usually limpet mines are set off by a time fuse. They may also have an anti-handling device, making the mine explode if removed from the hull by enemy divers or by explosions. Sometimes the limpet mine was fitted with a small turbine which would detonate the mine after the ship had sailed a certain distance, so that it was likely to sink in navigable channels or deep water out of reach of easy salvage. Thus, determining the cause of the sinking is more difficult.Patella caerulea
Patella caerulea, is a species of limpet in the family Patellidae. It is known by the common names Mediterranean limpet and rayed Mediterranean limpet. It is native to the Mediterranean Sea.Patella ferruginea
Patella ferruginea, common name Ribbed Mediterranean Limpet is a species of sea snail, a true limpet, a marine gastropod mollusk in the family Patellidae, one of the families of true limpets.Patella rustica
Patella rustica, common name rustic limpet is a species of sea snail, a true limpet, a marine gastropod mollusk in the family Patellidae, one of the families of true limpets.Patella ulyssiponensis
Patella ulyssiponensis, common name the rough limpet, or China limpet is a species of sea snail, a true limpet, a marine gastropod mollusk in the family Patellidae, one of the families of true limpets.Compared with the common limpet, Patella vulgata, the rough limpet has a similar shell (maximum size 50mm long x 40 mm wide x 20 mm high, apex closer to the front of the animal/ anterior than to the back/ posterior) but with radiating ridges that are finer and which alternate 1-ridge/ 3-ridges around the shell in a distinct pattern. The interior of the shell is often tinged orange towards its apex. The foot is a cream-orange color, and the dozens of pallial tentacles are translucent and colorless, arranged in two series of different sizes. No other characteristics of body structure or shell morphology distinguish it from P. vulgata, to which it is otherwise identical.Patella vulgata
Patella vulgata, common name the common limpet or common European limpet is an edible species of sea snail with gills, a typical true limpet, a marine gastropod mollusc in the family Patellidae.This species is found in the waters of western Europe.Patellogastropoda
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.The clade Patellogastropoda is deemed monophyletic based on phylogenetic analysis.Siphonariidae
Siphonariidae, also known as false limpets, are a taxonomic family of small to medium-sized air-breathing sea snails, marine and brackish water pulmonate gastropod molluscs.The Incredible Mr. Limpet
The Incredible Mr. Limpet is a 1964 American live-action/animated adventure film from Warner Bros. based on the 1942 novel, "Mr. Limpet" by Theodore Pratt. It is about a man named Henry Limpet who turns into a talking fish resembling a tilefish and helps the U.S. Navy locate and destroy Nazi submarines. Don Knotts plays the title character. The live action was directed by Arthur Lubin, while the animation was directed by Bill Tytla, Robert McKimson, Hawley Pratt, and Gerry Chiniquy. Music includes songs by Sammy Fain, in collaboration with Harold Adamson, including "I Wish I Were a Fish," "Be Careful How You Wish," and "Deep Rapture."