Get Our Extension
Select Wikiz in another Language
DeutschEspañolSuomiFrançaisעבריתItalianoNederlands
Settings
A
A
Text Highlights
Notes/Citations
Edit on Wikipedia

Share This Article

About Wikiz About Us Cookies Policy Terms & Services Privacy Policy Contact Contact us Enjoying Wikipedia Content? DONATE TO WIKIPEDIA
Enjoying Wikipedia Content? DONATE TO WIKIPEDIA

Radula

From Wikipedia, in a visual modern way
For the plant genus, see Radula (plant).

The radula (US: /ˈrædʒʊlə/; plural radulae or radulas)[1] is an anatomical structure used by mollusks for feeding, sometimes compared to a tongue.[2] 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 mollusks, and is found in every class of mollusk except the bivalves, which instead use cilia, waving filaments that bring minute organisms to the mouth.

Within the gastropods, the radula is used in feeding by both herbivorous and carnivorous snails and slugs. The arrangement of teeth (denticles) on the radular ribbon varies considerably from one group to another.

In most of the more ancient lineages of gastropods, the radula is used to graze, by scraping diatoms and other microscopic algae off rock surfaces and other substrates.

Predatory marine snails such as the Naticidae use the radula plus an acidic secretion to bore through the shell of other mollusks. Other predatory marine snails, such as the Conidae, use a specialized radular tooth as a poisoned harpoon. Predatory pulmonate land slugs, such as the ghost slug, use elongated razor-sharp teeth on the radula to seize and devour earthworms. Predatory cephalopods, such as squid, use the radula for cutting prey.

The introduction of the term "radula" (Latin, "little scraper") is usually attributed to Alexander von Middendorff in 1847.[3]

Discover more about Radula related topics

American English

American English

American English, sometimes called United States English or U.S. English, is the set of varieties of the English language native to the United States. English is the most widely spoken language in the United States and in most circumstances is the de facto common language used in government, education and commerce. Since the 20th century, American English has become the most influential form of English worldwide.

Mollusca

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 estimated between 60,000 and 100,000 additional species. The proportion of undescribed species is very high. Many taxa remain poorly studied.

Chitin

Chitin

Chitin (C8H13O5N)n ( KY-tin) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chitin are produced each year in the biosphere. It is a primary component of cell walls in fungi (especially basidiomycetes and filamentous fungi), the exoskeletons of arthropods such as crustaceans and insects, the radulae, cephalopod beaks and gladii of molluscs and in some nematodes and diatoms. It is also synthesised by at least some fish and lissamphibians. Commercially, chitin is extracted from the shells of crabs, shrimps, shellfish and lobsters, which are major by-products of the seafood industry. The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. Chitin has proved useful for several medicinal, industrial and biotechnological purposes.

Esophagus

Esophagus

The esophagus or oesophagus, 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 stomach. The esophagus is a fibromuscular tube, about 25 cm (10 in) long in adults, that travels behind the trachea and heart, passes through the diaphragm, and empties into the uppermost region of the stomach. During swallowing, the epiglottis tilts backwards to prevent food from going down the larynx and lungs. The word oesophagus is from Ancient Greek οἰσοφάγος (oisophágos), from οἴσω (oísō), future form of φέρω + ἔφαγον.

Bivalvia

Bivalvia

Bivalvia, in previous centuries referred to as the Lamellibranchiata and Pelecypoda, is a class of marine and freshwater molluscs that have laterally compressed bodies enclosed by a shell consisting of two hinged parts. As a group, bivalves have no head and they lack some usual molluscan organs, like the radula and the odontophore. The class includes the clams, oysters, cockles, mussels, scallops, and numerous other families that live in saltwater, as well as a number of families that live in freshwater. The majority are filter feeders. The gills have evolved into ctenidia, specialised organs for feeding and breathing. Most bivalves bury themselves in sediment, where they are relatively safe from predation. Others lie on the sea floor or attach themselves to rocks or other hard surfaces. Some bivalves, such as the scallops and file shells, can swim. The shipworms bore into wood, clay, or stone and live inside these substances.

Herbivore

Herbivore

A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthparts adapted to rasping or grinding. Horses and other herbivores have wide flat teeth that are adapted to grinding grass, tree bark, and other tough plant material.

Carnivore

Carnivore

A carnivore, or meat-eater, is an animal or plant whose food and energy requirements derive from animal tissues whether through hunting or scavenging.

Denticle (tooth feature)

Denticle (tooth feature)

Denticles, also called serrations, are small bumps on a tooth that serve to give the tooth a serrated edge. In paleontology, denticle characteristics such as size and density are used to describe and classify fossilized teeth, especially those of dinosaurs. Denticles are also present on the teeth of varanoid lizards, sharks, and mammals. The term is also used to describe the analogous radular teeth of mollusks.

Diatom

Diatom

A diatom is any member of a large group comprising several genera of algae, specifically microalgae, found in the oceans, waterways and soils of the world. Living diatoms make up a significant portion of the Earth's biomass: they generate about 20 to 50 percent of the oxygen produced on the planet each year, take in over 6.7 billion metric tons of silicon each year from the waters in which they live, and constitute nearly half of the organic material found in the oceans. The shells of dead diatoms can reach as much as a half-mile deep on the ocean floor, and the entire Amazon basin is fertilized annually by 27 million tons of diatom shell dust transported by transatlantic winds from the African Sahara, much of it from the Bodélé Depression, which was once made up of a system of fresh-water lakes.

Naticidae

Naticidae

Naticidae, common name moon snails or necklace shells, is a family of medium to large-sized predatory sea snails, marine gastropod molluscs in the clade Littorinimorpha. The shells of the species in this family are mostly globular in shape.

Conidae

Conidae

Conidae, with the current common name of "cone snails", is a taxonomic family of predatory sea snails, marine gastropod molluscs in the superfamily Conoidea.

Alexander von Middendorff

Alexander von Middendorff

Alexander Theodor von Middendorff was a zoologist and explorer of Baltic German and Estonian extraction. He is known for his expedition 1843–45 to the extreme north and east of Siberia, describing the effects of permafrost on the spread of animals and plants.

Components

A typical radula comprises a number of bilaterally-symmetrical self-similar rows of teeth rooted in a radular membrane in the floor of their mouth cavity. Some species have teeth that bend with the membrane as it moves over the odontophore, whereas in other species, the teeth are firmly rooted in place, and the entire radular structure moves as one entity.[4]

Radular membrane

The elastic, delicate radular membrane may be a single tongue, or may split into two (bipartite).[5]

Hyaline shield

See Hyaline shield for more details.

Odontophore

The odontophore is the eversible, fleshy tongue underlying the radular membrane. It controls the organ's protrusion and return. It can be likened to a pulley wheel over which the radular 'string' is pulled.[6]

Flexibility

The radular teeth can generally bend in a sideways direction. In the patellogastropods, though, the teeth lost this ability and became fixed.[6]

Teeth

The radula comprises multiple, identical (or near-enough) rows of teeth, fine, flat, or spiney out-growths; often, each tooth in a row (along with its symmetric partner) will have a unique morphology.

Each tooth can be divided into three sections: a base, a shaft, and a cusp. In radulae that just sweep, rather than rasp, the underlying substrate, the shaft and cusp are often continuous and cannot be differentiated.[7]

The teeth often tesselate with their neighbours, and this interlocking serves to make it more difficult to remove them from the radular ribbon.[7]

Radula formulae

Radula and individual tooth of the predatory ghost slug, Selenochlamys ysbryda
Radula and individual tooth of the predatory ghost slug, Selenochlamys ysbryda

The number, shape, and specialized arrangement of molluskan teeth in each transverse row is consistent on a radula, and the different patterns can be used as a diagnostic characteristic to identify the species in many cases.

Each row of radular teeth consists of

  • One central or median tooth (or rachidian tooth, rachis tooth)
  • On each side: one or more lateral teeth
  • And then beyond that: one or more marginal teeth.

This arrangement is expressed in a radular tooth formula, with the following abbreviations :

  • R : designates the central tooth or the rachis tooth (in case of lack of central tooth : the zero sign 0)
  • the lateral teeth on each side are expressed by a specific number or D, in case the outer lateral tooth is dominant.
  • the marginal teeth are designated by a specific number or, in case they are in a very large numbers, the infinity symbol ∞
Microscopic detail of a docoglossan radula showing the denticles or teeth
Microscopic detail of a docoglossan radula showing the denticles or teeth

This can be expressed in a typical formula such as:

3 + D + 2 + R + 2 + D + 3

This formula means: Across the radula there are 3 marginal teeth, 1 dominant lateral tooth, 2 lateral teeth, and one central tooth.

Another formula for describing radulae omits the use of letters and simply gives a sequence of numbers in the order marginal-lateral-rachidian-lateral-marginal, thus:

1-1-1-1-1

This particular formula, which is common to the scaphopods, means one marginal tooth, one lateral tooth, one rachidian tooth, one lateral tooth, and one marginal tooth across the ribbon.[8]

Morphology

The morphology of the radula is related to diet. However, it is not fixed per species; some mollusks can adapt the form of their radular teeth according to which food sources are abundant.[9]

Pointed teeth are best suited to grazing on algal tissue, whereas blunt teeth are preferable if feeding habits entail scraping epiphytes from surfaces.[9]

Use

Tracks made by terrestrial gastropods with their radulas, scraping green algae from a surface inside a greenhouse
Tracks made by terrestrial gastropods with their radulas, scraping green algae from a surface inside a greenhouse

The radula is used in two main ways: either as a rake, generally to comb up microscopic, filamentous algae from a surface; or as a rasp, to feed directly on a plant.[10] The rhipidoglossan (see below) and, to a lesser extent, the taenigloissan radular types are suited to less strenuous modes of feeding, brushing up smaller algae or feeding on soft forms; mollusks with such radulae are rarely able to feed on leathery or coralline algae. On the other hand, the docoglossan gastropod radula allows a very similar diet to the polyplacophora, feeding primarily on these resistant algae, although microalgae are also consumed by species with these radular types.[10]

The sacoglossans (sea slugs) form an interesting anomaly in that their radula comprises a single row; they feed by sucking on cell contents, rather than rasping at tissue, and most species feed on a single genus or species of alga. Here, the shape of the radular teeth has a close match with the food substrate on which they are used. Triangular teeth are suited to diets of calcified algae, and are also present in radulae used to graze on Caulerpa; in both these cases the cell walls are predominantly composed of xylan. Sabot-shaped teeth – rods with a groove along one side – are associated with diets of crossed-fibrillar cellulose-walled algae, such as the Siphonocladaceae and Cladophorales, whereas blade-shaped teeth are more generalist.[11]

Discover more about Use related topics

Sacoglossa

Sacoglossa

Sacoglossa, commonly known as the sacoglossans or the "solar-powered sea slugs", are a superorder of small sea slugs and sea snails, marine gastropod mollusks that belong to the clade Heterobranchia. Sacoglossans live by ingesting the cellular contents of algae, hence they are sometimes called "sap-sucking sea slugs".

Sea slug

Sea slug

Sea slug is a common name for some marine invertebrates with varying levels of resemblance to terrestrial slugs. Most creatures known as sea slugs are gastropods, i.e. they are sea snails that over evolutionary time have either completely lost their shells, or have seemingly lost their shells due to having a greatly reduced or internal shell. The name "sea slug" is most often applied to nudibranchs, as well as to a paraphyletic set of other marine gastropods without obvious shells.

Caulerpa

Caulerpa

Caulerpa is a genus of seaweeds in the family Caulerpaceae. They are unusual because they consist of only one cell with many nuclei, making them among the biggest single cells in the world. A species in the Mediterranean can have a stolon more than 3 metres (9.8 ft) long, with up to 200 fronds. This species can be invasive from time to time.

Xylan

Xylan

Xylan is a type of hemicellulose, a polysaccharide consisting mainly of xylose residues. It is found in plants, in the secondary cell walls of dicots and all cell walls of grasses. Xylan is the third most abundant biopolymer on Earth, after cellulose and chitin.

Sabot (firearms)

Sabot (firearms)

A sabot is a supportive device used in firearm/artillery ammunitions to fit/patch around a projectile, such as a bullet/slug or a flechette-like projectile, and keep it aligned in the center of the barrel when fired. It allows a narrower projectile with high sectional density to be fired through a barrel of much larger bore diameter with maximal accelerative transfer of kinetic energy. After leaving the muzzle, the sabot typically separates from the projectile in flight, diverting only a very small portion of the overall kinetic energy.

Siphonocladaceae

Siphonocladaceae

Siphonocladaceae is a family of green algae, in the order Cladophorales.

Cladophorales

Cladophorales

Cladophorales are an order of green algae, in the class Ulvophyceae.

Early mollusks

The first bona fide radula dates to the Early Cambrian,[12] although trace fossils from the earlier Ediacaran have been suggested to have been made by the radula of the organism Kimberella.

A so-called radula from the early Cambrian was discovered in 1974, this one preserved with fragments of the mineral ilmenite suspended in a quartz matrix, and showing similarities to the radula of the modern cephalopod Sepia.[13] However, this was since re-interpreted as Salterella.[14] [/Volborthella?]

Based on the bipartite nature of the radular dentition pattern in solenogasters, larval gastropods and larval polyplacophora, it has been postulated that the ancestral mollusk bore a bipartite radula (although the radular membrane may not have been bipartite).[5]

Discover more about Early mollusks related topics

Ediacaran

Ediacaran

The Ediacaran Period is a geological period that spans 96 million years from the end of the Cryogenian Period 635 million years ago (Mya), to the beginning of the Cambrian Period 538.8 Mya. It marks the end of the Proterozoic Eon, and the beginning of the Phanerozoic Eon. It is named after the Ediacara Hills of South Australia.

Kimberella

Kimberella

Kimberella is an extinct genus of bilaterian known only from rocks of the Ediacaran period. The slug-like organism fed by scratching the microbial surface on which it dwelt in a manner similar to the gastropods, although its affinity with this group is contentious.

Ilmenite

Ilmenite

Ilmenite is a titanium-iron oxide mineral with the idealized formula FeTiO3. It is a weakly magnetic black or steel-gray solid. Ilmenite is the most important ore of titanium and the main source of titanium dioxide, which is used in paints, printing inks, fabrics, plastics, paper, sunscreen, food and cosmetics.

Quartz

Quartz

Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical formula of SiO2. Quartz is the second most abundant mineral in Earth's continental crust, behind feldspar.

Salterella

Salterella

Salterella is an enigmatic Cambrian genus with a small, conical, calcareous shell that appears to be septate, but is rather filled with stratified laminar deposits. The shell contains grains of sediment, which are obtained selectively by a manner also observed in foramanifera. The genus was established by Elkanah Billings in 1861, and was named after the English palaeontologist John William Salter.

Volborthella

Volborthella

Volborthella is an animal of uncertain classification, whose fossils pre-date 530 million years ago. It has been considered for a period a cephalopod. However discoveries of more detailed fossils showed that Volborthella’s small, conical shell was not secreted but built from grains of the mineral silicon dioxide (silica), and that it was not divided into a series of compartments by septa as those of fossil shelled cephalopods and the living Nautilus are. This illusion was a result of the laminated texture of the organisms' tests. Therefore, Volborthella’s classification is now uncertain. It has been speculated that it may in fact represent a sclerite of a larger organism, on the basis of one specimen; however, it may be premature to accept this hypothesis, as the arrangement of sclerites producing this impression may have occurred by chance. The Ordovician scleritome-bearing Curviconophorus, as well as the Halwaxiids, lobopods and echinoderms, demonstrate the diversity of organisms which may produce a scleritome of this nature. The related Campitius was originally suggested to be part of a radula rather than a scleritome, but is now considered a synonym of Volborthella.

In chitons

Each row of the polyplacophoran radula has two mineralized teeth used to abrade the substrate, and two longer teeth that sweep up any debris. The other 13 teeth on each row do not appear to be involved in feeding.[10]

The teeth of Chaetopleura apiculata comprise fibres surrounded by magnetite, sodium and magnesium.[15]

Discover more about In chitons related topics

Chaetopleura apiculata

Chaetopleura apiculata

Chaetopleura apiculata is a species of small chiton in the family Chaetopleuridae. It is a marine mollusc.

Magnetite

Magnetite

Magnetite is a mineral and one of the main iron ores, with the chemical formula Fe2+Fe3+2O4. It is one of the oxides of iron, and is ferrimagnetic; it is attracted to a magnet and can be magnetized to become a permanent magnet itself. With the exception of extremely rare native iron deposits, it is the most magnetic of all the naturally occurring minerals on Earth. Naturally magnetized pieces of magnetite, called lodestone, will attract small pieces of iron, which is how ancient peoples first discovered the property of magnetism.

Sodium

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 of the periodic table. Its only stable isotope is 23Na. The free metal does not occur in nature, and must be prepared from compounds. Sodium is the sixth most abundant element in the Earth's crust and exists in numerous minerals such as feldspars, sodalite, and halite (NaCl). Many salts of sodium are highly water-soluble: sodium ions have been leached by the action of water from the Earth's minerals over eons, and thus sodium and chlorine are the most common dissolved elements by weight in the oceans.

Magnesium

Magnesium

Magnesium is a chemical element with the symbol Mg and atomic number 12. It is a shiny gray metal having a low density, low melting point and high chemical reactivity. Like the other alkaline earth metals it occurs naturally only in combination with other elements and it almost always has an oxidation state of +2. It reacts readily with air to form a thin passivation coating of magnesium oxide that inhibits further corrosion of the metal. The free metal burns with a brilliant-white light. The metal is obtained mainly by electrolysis of magnesium salts obtained from brine. It is less dense than aluminium and is used primarily as a component in strong and lightweight alloys that contain aluminium.

In gastropods

Diagrammatic transverse view of the buccal cavity of a gastropod, showing the radula and how it is used. The rest of the body of the snail is shown in green. The food is shown in blue. Muscles that control the radula are shown in brown. The surface of the radular ribbon, with numerous teeth, is shown as a zig-zag line
Diagrammatic transverse view of the buccal cavity of a gastropod, showing the radula and how it is used.
The rest of the body of the snail is shown in green. The food is shown in blue. Muscles that control the radula are shown in brown. The surface of the radular ribbon, with numerous teeth, is shown as a zig-zag line
Upper right: Mouth of a Planorbarius corneus freshwater snail with the radula visible.
Upper right: Mouth of a Planorbarius corneus freshwater snail with the radula visible.
Further information: Digestive system of gastropods

Anatomy and method of functioning

The mouth of the gastropods is located below the anterior part of the mollusk. It opens into a pocket-like buccal cavity, containing the radular sac, an evaginated pocket in the posterior wall of this cavity.

The radula apparatus consists of two parts :

  • the cartilaginous base (the odontophore), with the odontophore protractor muscle, the radula protractor muscle and the radula retractor muscle.
  • the radula itself, with its longitudinal rows of chitinous and recurved teeth, the cuticula.

The odontophore is movable and protractible, and the radula itself is movable over the odontophore. Through this action the radular teeth are being erected. The tip of the odontophore then scrapes the surface, while the teeth cut and scoop up the food and convey the particles through the esophagus to the digestive tract.

In a flexoglossate radula (the primitive condition), the teeth flex outwards to the sides as they round the tip of the odontophore, before flexing back inwards. In the derived stereoglossate condition, the teeth do not flex.[6]

These actions continually wear down the frontal teeth. New teeth are continuously formed at the posterior end of the buccal cavity in the radular sac. They are slowly brought forward to the tip by a slow forward movement of the ribbon, to be replaced in their turn when they are worn out.

Teeth-production is rapid (some species produce up to five rows per day). The radular teeth are produced by odontoblasts, cells in the radular sac.

The number of teeth present depends on the species of mollusk and may number more than 100000. Large numbers of teeth in a row (actually v-shaped on the ribbon in many species) is presumed to be a more primitive condition, but this may not always be true.

The greatest number of teeth per row is found in Pleurotomaria (deep water gastropods in an ancient lineage) which has over 200 teeth per row (Hyman, 1967).

The shape and arrangement of the radular teeth is an adaptation to the feeding regimen of the species.

The teeth of the radula are lubricated by the mucus of the salivary gland, just above the radula. Food particles are trapped into this sticky mucus, smoothing the progress of food into the esophagus.

Certain gastropods use their radular teeth to hunt other gastropods and bivalve mollusks, scraping away the soft parts for ingestion. Cone shells have a single radular tooth, that can be thrust like a harpoon into its prey, releasing a neurotoxin.

Seven basic types

  • The docoglossan or stereoglossan radula: in each row there is one usually small central tooth, flanked by 1–3 laterals (with the outer one dominant) and a few (3 at the most) hooked marginals. The central tooth may even be absent. The teeth are fixed in a stiff position on the radular ribbon. This is the most primitive radular type, and we could assume it represents the plesiomorphic condition i.e., the primitive character state, that is taken from an ancestor without change, such as would be possessed by the earliest mollusks (Eogastropoda, also Polyplacophora; limpet families Patellidae, Lottiidae, Lepetidae). The radula operates like a chain of 'shovels', and the rigid structure operates like a rasp, scraping at hardened macroalgae.[10] Accordingly, docoglossan radulae are often hardened by biomineralization.[10] Spaces between the teeth make the radula ill-suited to collecting microalgae.[10]
    • Formula: 3 + D + 2 + R + 2 + D + 3
    • Or: 3 + D + 2 + 0 + 2 + D + 3
  • Rhipidoglossan radula: a large central and symmetrical tooth, flanked on each side by several (usually five) lateral teeth and numerous closely packed flabellate marginals, called uncini (typical examples: Vetigastropoda, Neritomorpha). This already marks an improvement over the simple docoglossan state. These radulae generally operate like 'brooms', brushing up loose microalgae.[10]
    • Formula: ∞ + 5 + R + 5 + ∞
    • In case of a dominant lateral tooth: ∞ + D + 4 + R + 4 + D + ∞
Radula (magn. 400x) of the gray garden slug (Deroceras laeve) showing the chitinous lingual ribbons with numerous inward-pointing denticles
Radula (magn. 400x) of the gray garden slug (Deroceras laeve) showing the chitinous lingual ribbons with numerous inward-pointing denticles
  • Hystrichoglossan radula: each row with lamellate and hooked lateral teeth and hundreds of uniform marginal teeth that are tufted at their ends (typical example : Pleurotomariidae).
    • The radular formula of, for example, Pleurotomaria (Entemnotrochus) rumphii is : ∞. 14. 27. 1. 27. 14. ∞
  • Taenioglossan radula: seven teeth in each row: one middle tooth, flanked on each side by one lateral and two marginal teeth (characteristic of the majority of the Caenogastropoda). These operate like 'rakes', scraping algae and gathering the resultant detritus.[10]
    • Formula : 2 + 1 + R + 1 + 2
  • Ptenoglossan radula: rows with no central tooth but a series of several uniform, pointed marginal teeth (typical example : Epitonioidea).
    • Formula : n + 0 + n
  • Stenoglossan or rachiglossan radula: each row has one central tooth and one lateral tooth on each side (or no lateral teeth in some cases) (most Neogastropoda).
    • Formula : 1 + R + 1
    • Or : 0 + R + 0
  • Toxoglossan radula: The middle teeth are very small or completely absent. Each row has only two teeth of which only one is in use at a time. These grooved teeth are very long and pointed, with venom channels (neurotoxins) and barbs, and are not firmly fixed to the basal plate. The teeth can therefore be individually transferred to the proboscis and ejected like a harpoon into the prey (typical example : Conoidea).
    • formula : 1 + 0 + 1

These radular types show the evolution in the gastropods from herbivorous to carnivorous feeding patterns. Scraping algae requires many teeth, as is found in the first three types.

Carnivorous gastropods generally need fewer teeth, especially laterals and marginals. The ptenoglossan radula is situated between the two extremes and is typical for those gastropods which are adapted to a life as parasites on polyps.

A portion of the radula of Marstonia comalensis showing outer marginal teeth (on the left), inner marginal teeth and immediately next to them lateral teeth, central teeth. Scale bar is 20 μm.
A portion of the radula of Marstonia comalensis showing outer marginal teeth (on the left), inner marginal teeth and immediately next to them lateral teeth, central teeth. Scale bar is 20 μm.
Inner marginal tooth. Scale bar is 10 μm.
Inner marginal tooth. Scale bar is 10 μm.
Lateral teeth. Scale bar is 10 μm.
Lateral teeth. Scale bar is 10 μm.
Central teeth. Scale bar is 10 μm.
Central teeth. Scale bar is 10 μm.

Gastropods with no radula

The streptaxid Careoradula perelegans is the only known terrestrial gastropod which has no radula.[16]

Some marine gastropods lack a radula. For example, all species of sea slugs in the family Tethydidae have no radula,[17] and a clade of dorids (the Porostomata)[18] as well as all species of the genus Clathromangelia (family Clathurellidae)[19] likewise lack the organ. The radula has been lost a number of times in the Opisthobrancha.[20]

Discover more about In gastropods related topics

Planorbarius corneus

Planorbarius corneus

Planorbarius corneus, common name the great ramshorn, is a relatively large species of air-breathing freshwater snail, an aquatic pulmonate gastropod mollusk in the family Planorbidae, the ram's horn snails, or planorbids, which all have sinistral or left-coiling shells.

Digestive system of gastropods

Digestive system of gastropods

The digestive system of gastropods has evolved to suit almost every kind of diet and feeding behavior. Gastropods as the largest taxonomic class of the mollusca are very diverse: the group includes carnivores, herbivores, scavengers, filter feeders, and even parasites.

Chitin

Chitin

Chitin (C8H13O5N)n ( KY-tin) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chitin are produced each year in the biosphere. It is a primary component of cell walls in fungi (especially basidiomycetes and filamentous fungi), the exoskeletons of arthropods such as crustaceans and insects, the radulae, cephalopod beaks and gladii of molluscs and in some nematodes and diatoms. It is also synthesised by at least some fish and lissamphibians. Commercially, chitin is extracted from the shells of crabs, shrimps, shellfish and lobsters, which are major by-products of the seafood industry. The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. Chitin has proved useful for several medicinal, industrial and biotechnological purposes.

Esophagus

Esophagus

The esophagus or oesophagus, 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 stomach. The esophagus is a fibromuscular tube, about 25 cm (10 in) long in adults, that travels behind the trachea and heart, passes through the diaphragm, and empties into the uppermost region of the stomach. During swallowing, the epiglottis tilts backwards to prevent food from going down the larynx and lungs. The word oesophagus is from Ancient Greek οἰσοφάγος (oisophágos), from οἴσω (oísō), future form of φέρω + ἔφαγον.

Mucus

Mucus

Mucus is a slippery aqueous secretion produced by, and covering, mucous membranes. It is typically produced from cells found in mucous glands, although it may also originate from mixed glands, which contain both serous and mucous cells. It is a viscous colloid containing inorganic salts, antimicrobial enzymes, immunoglobulins, and glycoproteins such as lactoferrin and mucins, which are produced by goblet cells in the mucous membranes and submucosal glands. Mucus serves to protect epithelial cells in the linings of the respiratory, digestive, and urogenital systems, and structures in the visual and auditory systems from pathogenic fungi, bacteria and viruses. Most of the mucus in the body is produced in the gastrointestinal tract.

Neurotoxin

Neurotoxin

Neurotoxins are toxins that are destructive to nerve tissue. Neurotoxins are an extensive class of exogenous chemical neurological insults that can adversely affect function in both developing and mature nervous tissue. The term can also be used to classify endogenous compounds, which, when abnormally contacted, can prove neurologically toxic. Though neurotoxins are often neurologically destructive, their ability to specifically target neural components is important in the study of nervous systems. Common examples of neurotoxins include lead, ethanol, glutamate, nitric oxide, botulinum toxin, tetanus toxin, and tetrodotoxin. Some substances such as nitric oxide and glutamate are in fact essential for proper function of the body and only exert neurotoxic effects at excessive concentrations.

Eogastropoda

Eogastropoda

Eogastropoda was a previously used taxonomic category of snails or gastropods, a subclass which was erected by Ponder and Lindberg in 1997. It was one of two great divisions (subclasses) of the class Gastropoda, the snails. The other subclass of gastropods was the Orthogastropoda.

Patellidae

Patellidae

Patellidae is a taxonomic family of sea snails or true limpets, marine gastropod molluscs in the clade Patellogastropoda.

Lottiidae

Lottiidae

Lottiidae is a family of sea snails, specifically true limpets, marine gastropod mollusks in the superfamily Lottioidea and the clade Patellogastropoda.

Lepetidae

Lepetidae

Lepetidae is a family of sea snails or small, deep-water true limpets, marine gastropod molluscs in the clade Patellogastropoda the true limpets.

Deroceras laeve

Deroceras laeve

Deroceras laeve, the marsh slug, is a species of small air-breathing land slug, a terrestrial pulmonate gastropod mollusk in the family Agriolimacidae.

Pleurotomaria

Pleurotomaria

Pleurotomaria is an extinct genus of sea snails, marine gastropod molluscs in the family Pleurotomariidae.

In cephalopods

Radular teeth of the squid Illex illecebrosus
Radular teeth of the squid Illex illecebrosus

Most cephalopods possess a radula as well as a horny chitinous beak,[21] although the radula is reduced in octopuses and absent in Spirula.[22]: 110 

The cephalopod radula rarely fossilizes: it has been found in around one in five ammonite genera, and is rarer still in non-ammonoid forms. Indeed, it is known from only three non-ammonoid taxa in the Palaeozoic era: Michelinoceras, Paleocadmus, and an unnamed species from the Soom Shale.[23]

Discover more about In cephalopods related topics

Illex illecebrosus

Illex illecebrosus

Illex illecebrosus, commonly known as the northern shortfin squid, is a species of neritic squids in the family Ommastrephidae. Squids of the genus Illex account for 65% of the world’s cephalopod captures. Illex is formed by four taxa distributed throughout the Atlantic Ocean, whose identification and phylogenetic relationships based on morphological characters remain controversial.They are found in the northwest Atlantic Ocean, from off the coast of eastern North America to Greenland, Iceland, and west of Ireland and the United Kingdom. They are a highly migratory and short-lived species, with lifespans of less than a year. They are commercially important and are fished extensively, mostly for the Canadian and Japanese markets. Northern shortfin squid is a migratory species of squid with a distribution ranging from Florida Straits to Newfoundland in the Northwest Atlantic Ocean. The species is native to Canada, Greenland, Iceland and United States. The species has an average lifespan between 1–1.5 years in which most live less than a year. The location of the fishery of the squid is mainly in Mid-Atlantic Bight from between summer and fall.

Cephalopod

Cephalopod

A cephalopod is any member of the molluscan class Cephalopoda such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot. Fishers sometimes call cephalopods "inkfish", referring to their common ability to squirt ink. The study of cephalopods is a branch of malacology known as teuthology.

Chitin

Chitin

Chitin (C8H13O5N)n ( KY-tin) is a long-chain polymer of N-acetylglucosamine, an amide derivative of glucose. Chitin is probably the second most abundant polysaccharide in nature (behind only cellulose); an estimated 1 billion tons of chitin are produced each year in the biosphere. It is a primary component of cell walls in fungi (especially basidiomycetes and filamentous fungi), the exoskeletons of arthropods such as crustaceans and insects, the radulae, cephalopod beaks and gladii of molluscs and in some nematodes and diatoms. It is also synthesised by at least some fish and lissamphibians. Commercially, chitin is extracted from the shells of crabs, shrimps, shellfish and lobsters, which are major by-products of the seafood industry. The structure of chitin is comparable to cellulose, forming crystalline nanofibrils or whiskers. It is functionally comparable to the protein keratin. Chitin has proved useful for several medicinal, industrial and biotechnological purposes.

Cephalopod beak

Cephalopod beak

All extant cephalopods have a two-part beak, or rostrum, situated in the buccal mass and surrounded by the muscular head appendages. The dorsal (upper) mandible fits into the ventral (lower) mandible and together they function in a scissor-like fashion. The beak may also be referred to as the mandibles or jaws.

Octopus

Octopus

An octopus is a soft-bodied, eight-limbed mollusc of the order Octopoda. The order consists of some 300 species and is grouped within the class Cephalopoda with squids, cuttlefish, and nautiloids. Like other cephalopods, an octopus is bilaterally symmetric with two eyes and a beaked mouth at the center point of the eight limbs. The soft body can radically alter its shape, enabling octopuses to squeeze through small gaps. They trail their eight appendages behind them as they swim. The siphon is used both for respiration and for locomotion, by expelling a jet of water. Octopuses have a complex nervous system and excellent sight, and are among the most intelligent and behaviourally diverse of all invertebrates.

Spirula

Spirula

Spirula spirula is a species of deep-water squid-like cephalopod mollusk. It is the only extant member of the genus Spirula, the family Spirulidae, and the order Spirulida. Because of the shape of its internal shell, it is commonly known as the ram's horn squid or the little post horn squid. Because the live animal has a light-emitting organ, it is also sometimes known as the tail-light squid.

Michelinoceras

Michelinoceras

Michelinoceras is the oldest known genus of the Michelinocerida, more commonly known as the Orthocerida, characterized by long, slender, nearly cylindrical orthocones with a circular cross section, long camerae, very long body chambers, and a central or near central tubular siphuncle free of organic deposits. Septal necks are straight; connecting rings cylindrical and thin. Cameral deposits are well developed. A radula has been found in one species, with seven teeth per row. It had ten arms, two of which formed longer tentacles.

Paleocadmus

Paleocadmus

Paleocadmus is a genus of radula known only from the Mazon Creek biota. It is only known from isolated fossils around a centimetre in length, and a few mm wide, but its morphology aligns it with the nautiloids, or perhaps the bactritoids or belemnoids.

Soom Shale

Soom Shale

The Soom Shale is a member of the Late Ordovician (Hirnantian) Cederberg Formation in South Africa, renowned for its remarkable preservation of soft-tissue in fossil material. Deposited in still waters, the unit lacks bioturbation, perhaps indicating anoxic conditions.

In solenogasters

The solenogaster radula is akin to that of other mollusks, with regularly spaced rows of teeth produced at one end and shed at the other. The teeth within each row are similar in shape, and get larger in size towards the outer extreme. A number of teeth occur on each row; this number is usually constant but prone to small variations from row to row; indeed, it increases over time, with teeth being added to the middle of rows by addition or by the division of existing teeth.[5] A number of radular formulae are exhibited by this class: 1:0:1 is most common, followed by 0:1:0 and n:0:n.[5]

In caudofoveates

The radula of the caudofoveate Falcidens is unlike the conchiferan radula. It has a reduced form, comprising just a single row of teeth. On each side of the apparatus, two teeth appear at the front; behind these, the third teeth fuse to form a mineralized axial plate. Bars occur posterior to this, behind which a sheath encircles the apparatus. The rear of the apparatus consists of a large plate, the 'radular cone'.[24] The unusual form of the radula is accompanied by an unusual purpose: rather than rasping substrates, Falcidens uses its teeth as pincers to grasp prey items.[24]

Source: "Radula", Wikipedia, Wikimedia Foundation, (2023, March 16th), https://en.wikipedia.org/wiki/Radula.

Enjoying Wikiz?

Enjoying Wikiz?

Get our FREE extension now!

Download Extension

Further Reading

Chiton

Kimberella

Wiwaxia

Tusk shell

Limpet

Conoidea

Evolution of molluscs

Solenogastres

Odontogriphus

Halwaxiida

Mollusca

Drilliidae

Tooth

Cerithium caeruleum

Odontophore

Hallaxa chani

Pontohedyle

Denticle (tooth feature)
See also
References
  1. ^ "Radula definitions". wordswarm.net. Retrieved 9 October 2009.
  2. ^ "All About Slugs".
  3. ^ (in German) von Middendorff A. T. (1847). Beiträge zu einer malacozoologia rossica: Chitonen. St. Petersburg, 151 pp. + plates. p .54.
  4. ^ Padilla, D. K. (1985). "Structural resistance of algae to herbivores". Marine Biology. 90: 103–109. doi:10.1007/BF00428220. S2CID 80717511.
  5. ^ a b c d Scheltema, A. H.; Kerth, K.; Kuzirian, A. M. (2003). "Original molluscan radula: Comparisons among Aplacophora, Polyplacophora, Gastropoda, and the Cambrian fossil Wiwaxia corrugata". Journal of Morphology. 257 (2): 219–245. doi:10.1002/jmor.10121. PMID 12833382. S2CID 32940079.
  6. ^ a b c Guralnick, R.; Smith, K. (1999). "Historical and biomechanical analysis of integration and dissociation in molluscan feeding, with special emphasis on the true limpets (Patellogastropoda: Gastropoda)". Journal of Morphology. 241 (2): 175–195. doi:10.1002/(SICI)1097-4687(199908)241:23.0.CO;2-0. PMID 10420163. S2CID 14497120.
  7. ^ a b Hickman, C. S. (1980). "Gastropod Radulae and the Assessment of Form in Evolutionary Paleontology". Paleobiology. 6 (3): 276–294. doi:10.1017/s0094837300006801. JSTOR 2400346. S2CID 89455588.
  8. ^ Shimek, Ronald; Steiner, Gerhard (1997). "Chapter 6". Microscopic anatomy of invertebrates. Vol. 6B: Mollusca II. Wiley-Liss, Inc. p. 748.
  9. ^ a b Padilla, D. K. (April 1998). "Inducible Phenotypic Plasticity of the Radula in Lacuna (Gastropoda: Littorinidae)" (PDF). The Veliger. 41 (2): 201–204.
  10. ^ a b c d e f g h Steneck, R. S.; Watling, L. (1982). "Feeding capabilities and limitation of herbivorous mollusks: A functional group approach". Marine Biology. 68 (3): 299–319. doi:10.1007/BF00409596. S2CID 84207061.
  11. ^ Jensen, K. R. (1993). "Morphological adaptations and plasticity of radular teeth of the Sacoglossa (= Ascoglossa) (Mollusca: Opisthobranchia) in relation to their food plants". Biological Journal of the Linnean Society. 48 (2): 135–155. doi:10.1111/j.1095-8312.1993.tb00883.x.
  12. ^ Butterfield, N.J. (2008). "An early Cambrian radula". Journal of Paleontology. 82 (3): 543–554. doi:10.1666/07-066.1. S2CID 86083492.
  13. ^ Firby, J. B.; Durham, J. W. (1 November 1974). "Molluscan Radula from Earliest Cambrian". Journal of Paleontology. 48 (6): 1109–1338. ISSN 0022-3360.
  14. ^ Yochelson, E. L.; Kisselev, G. N. (2003). "Early Cambrian Salterella and Volborthella (Phylum Agmata) re-evaluated". Lethaia. 36 (1): 8–20. doi:10.1080/00241160310001254.
  15. ^ Gordon, L. M.; Joester, D. (2011). "Nanoscale chemical tomography of buried organic–inorganic interfaces in the chiton tooth". Nature. 469 (7329): 194–197. Bibcode:2011Natur.469..194G. doi:10.1038/nature09686. PMID 21228873. S2CID 4430261.
  16. ^ Gerlach, J.; van Bruggen, A. C. (1998). "A first record of a terrestrial mollusk without a radula". Journal of Molluscan Studies. 64 (2): 249–250. doi:10.1093/mollus/64.2.249.
  17. ^ Rudman W. B. (14 October 2002) "http://www.seaslugforum.net/factsheet.cfm?base=tethfimb". Sea Slug Forum, accessed 29 December 2010.
  18. ^ Valdés, A. (2003). "Preliminary Molecular Phylogeny of the Radula-Less Dorids (Gastropoda: Opisthobranchia), Based on 16S Mtdna Sequence Data". Journal of Molluscan Studies. 69: 75–80. doi:10.1093/mollus/69.1.75.
  19. ^ Oliverio, M (1995). "The systematics of the radula-less gastropod Clathromangelia (Caenogastropoda, Conoidea)". Zoologica Scripta. 24 (3): 193–201. doi:10.1111/j.1463-6409.1995.tb00399.x. S2CID 85202876.
  20. ^ "Morphological Parallelism in Opisthobranch Gastropods". Malacologia: 313–327. 1991.
  21. ^ Brusca & Brusca. Invertebrates (2nd ed.).
  22. ^ Wilbur, Karl M.; Clarke, M.R.; Trueman, E.R., eds. (1985), The Mollusca, vol. 12. Paleontology and neontology of Cephalopods, New York: Academic Press, ISBN 0-12-728702-7
  23. ^ Gabbott, S. E. (1999). "Orthoconic cephalopods and associated fauna from the late Ordovician Soom Shale Lagerstatte, South Africa". Palaeontology. 42: 123–148. doi:10.1111/1475-4983.00065.
  24. ^ a b Cruz, R.; Lins, U.; Farina, M. (1998). "Minerals of the radular apparatus of Falcidens sp. (Caudofoveata) and the evolutionary implications for the Phylum Mollusca". Biological Bulletin. 194 (2): 224–230. doi:10.2307/1543051. JSTOR 1543051. PMID 28570844.
Further reading
External links
Wikimedia Commons has media related to Radula.
Look up radula in Wiktionary, the free dictionary.
Categories

The content of this page is based on the Wikipedia article written by contributors..
The text is available under the Creative Commons Attribution-ShareAlike Licence & the media files are available under their respective licenses; additional terms may apply.
By using this site, you agree to the Terms of Use & Privacy Policy.
Wikipedia® is a registered trademark of the Wikimedia Foundation, Inc., a non-profit organization & is not affiliated to WikiZ.com.