Limpet

The basic anatomy of a limpet consists of the usual molluscan organs and systems: • A nervous system centered around the paired cerebral, pedal, and pleural sets of ganglia. These ganglia create a ring around the limpet's esophagus called a circumesophageal nerve ring or nerve collar. Other nerves in the head/ snout are the optic nerves which connect to the two eye spots located at the base of the cerebral tentacles (these eyespots, when present, are only able to sense light and darkness and do not provide any imagery), as well as the labial and buccal ganglia which are associated with feeding and controlling the animal's odontophore, the muscular cushion used to support the limpet's radula (a kind of tongue) that scrapes algae off the surrounding rock for nutrition. Behind these ganglia lie the pedal nerve cords which control the movement of the foot, and the visceral ganglion which in limpets has been torted during the course of evolution. This means, among other things, that the limpet's left osphradium and oshradial ganglion (an organ believed used to sense the time to produce gametes) is controlled by its right pleural ganglion and vice versa. • For most limpets, the circulatory system is based around a single triangular three-chambered heart consisting of an atrium, a ventricle, and a bulbous aorta. Blood enters the atrium via the circumpallial vein (after being oxygenated by the ring of gills located around the edge of the shell) and through a series of small vesicles that deliver more oxygenated blood from the nuchal cavity (the area above the head and neck). Many limpets still retain a ctenidium (sometimes two) in this nuchal chamber instead of the circumpallial gills as a means for exchanging oxygen and carbon dioxide with the surrounding water or air (many limpets can breathe air during periods of low tide, but those limpet species which never leave the water do not have this ability and will suffocate if deprived of water). Blood moves from the atrium into the ventricle and into the aorta where it is then pumped out to the various lacunar blood spaces / sinuses in the hemocoel. The odontophore may play a large role in assisting with blood circulation as well. 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. 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. Teeth Function and formation 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) Growth and development 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.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. Strength Looking into limpet teeth of Patella vulgata, Vickers hardness values are between 268 and 646 kg⋅m−1⋅s−2, 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 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. Crystal structure Goethite crystals form 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". Crystallization process 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 goethite, however, has varying crystal habits. The crystals arrange in various shapes and thicknesses throughout the chitin matrix. 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%. 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. ==Taxonomy==

Gastropods that have limpet-like or patelliform shells are found in several different clades: • Clade Patellogastropoda, example Patellidae, the true limpets, all marine, in five living families and two fossil families • Clade Vetigastropoda, examples Fissurellidae, (the keyhole limpets and slit limpets), and Lepetelloidea, small deepwater limpets • Clade Neritimorpha, example Phenacolepadidae, small limpets related to nerites • Clade Heterobranchia, group Opisthobranchia, example Tylodinidae, the umbrella slugs with a limpet-shaped shell • Clade Heterobranchia, group Pulmonata, examples Siphonariidae, Latiidae, Trimusculidae, all air-breathing limpets Other limpets Marine • The hydrothermal vent limpets – Neomphaloidea and Lepetodriloidea • The hoof snails – Hipponix and other Hipponicidae • Slipper snails – Crepidula species, which are sometimes known as slipper limpets Freshwater • The pulmonate river and lake limpets – Ancylidae Some species of limpet live in fresh water, but these are the exception. 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. Naming 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, broadly conical shell, 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. ==Ecology==

Symbiosis Limpets have a mutualistic relationship with several other beings. Clathromorphum, a type of algae, provides food to limpets, which clean the algae's surface and allow its persistence. The rough keyhole limpet (Diodora aspera) is host to the scale worm copepod Anthessius nortoni, which bites predatory starfish to discourage them from eating the limpet. in their research paper titled Limpet erosion of chalk shore platforms in southeast England from Oct 2000 estimate from the amount of calcium carbonate deposits in faeces of captive limpets, that an adult limpet will ingest around 4.9 g of chalk per year. Suggesting that limpets are on average responsible for 12% of the chalk platform erosion in areas that they frequent, potentially rising to 35% + in areas where the limpet population has reached its maximum. ==In culture==

Some species of limpet may have been used historically to feed pigs. 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 film 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 film, 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. Cuisine Both Patella candei and Patella aspera are harvested for human consumption, mainly in the Portuguese Autonomous Regions of the Azores and Madeira. They are primarily eaten grilled with butter and garlic as the delicacy Lapas grelhadas (grilled limpets). ==References==