Insect mouthparts
Insects have a range of mouthparts, adapted to particular modes of feeding. The earliest insects had chewing mouthparts. Specialization has been for piercing and sucking, although a range of specializations exist, as these modes of feeding have evolved a number of times. In this page, the individual mouthparts are introduced for chewing insects. Specializations are described thereafter. Like most external features of arthropods, the mouthparts of hexapoda are derived. Insect mouthparts show a multitude of different functional mechanisms across the wide diversity of species considered insects, it is common for significant homology to be conserved, with matching structures formed from matching primordia, having the same evolutionary origin. On the other hand structures that physically are identical, share identical functionality as well, may not be homologous. Examples of chewing insects include dragonflies and beetles; some insects do not have chewing mouthparts as adults but do chew solid food when they feed while they still are larvae.
The moths and butterflies are major examples of such adaptations. A chewing insect has a pair of one on each side of the head; the mandibles are caudal to the anterior to the maxillae. The mandibles are the largest and most robust mouthparts of a chewing insect, it uses them to masticate food items. Two sets of muscles move the mandibles in the coronal plane: abductor muscles move insects' mandibles apart; this they do in opening and closing their jaws in feeding, but in using the mandibles as tools, or in fighting. In carnivorous chewing insects, the mandibles are serrated and knife-like, with piercing points. In herbivorous chewing insects mandibles tend to be broader and flatter on their opposing faces, as for example in caterpillars. In males of some species, such as of Lucanidae and some Cerambycidae, the mandibles are modified to such an extent that they do not serve any feeding function, but are instead used to defend mating sites from other males. In some ants and termites, the mandibles serve a defensive function.
In bull ants, the mandibles are toothed, used both as hunting appendages. In bees, that feed by use of a proboscis, the primary use of the mandibles is to manipulate and shape wax, many paper wasps have mandibles adapted to scraping and ingesting wood fibres. Situated beneath the mandibles, paired maxillae manipulate and, in chewing insects masticate, food; each maxilla consists of two parts, the proximal cardo, distal stipes. At the apex of each stipes are two lobes, the inner lacinia and outer galea. At the outer margin, the typical galea is a cupped or scoop-like structure, located over the outer edge of the labium. In non-chewing insects, such as adult Lepidoptera, the maxillae may be drastically adapted to other functions. Unlike the mandibles, but like the labium, the maxillae bear lateral palps on their stipites; these palps serve as organs of touch and taste in feeding, in inspection of potential foods. In chewing insects and abductor muscles extend from inside the cranium to within the bases of the stipites and cardines much as happens with the mandibles in feeding, in using the maxillae as tools.
To some extent the maxillae are more mobile than the mandibles, the galeae and palps can move up and down somewhat, in the sagittal plane, both in feeding and in working, for example in nest building by mud-dauber wasps. Maxillae in most insects function like mandibles in feeding, but they are more mobile and less sclerotised than mandibles, so they are more important in manipulating soft, liquid, or particulate food rather than cutting or crushing food such as material that requires the mandibles to cut or crush. Like the mandibles, maxillae are innervated by the sub-esopharyngeal ganglia; the labium is a quadrilateral structure, formed by paired, fused secondary maxillae. It is the major component of the floor of the mouth. Together with the maxillae, the labrum assists manipulation of food during mastication; the role of the labium in some insects however, is adapted to special functions. In these insects, the labium folds neatly beneath the head and thorax, but the insect can flick it out to snatch prey, inject venom to kill and digest the prey, to bear it back to the head, where the chewing mouthparts can demolish it and swallow the particles.
The labium is attached at the rear end of the structure called cibarium, its broad basal portion is divided into regions called the submentum, the proximal part, the mentum in the middle, the prementum, the distal section, furthest anterior. The prementum bears; these structures are homologous to the galea of maxillae. The labial palps borne on the sides of labium are the counterparts of maxillary pal
Hemiptera
The Hemiptera or true bugs are an order of insects comprising some 50,000 to 80,000 species of groups such as the cicadas, planthoppers and shield bugs. They range in size from 1 mm to around 15 cm, share a common arrangement of sucking mouthparts; the name "true bugs" is sometimes limited to the suborder Heteroptera. Many insects known as "bugs" belong to other orders. Most hemipterans feed on plants, piercing mouthparts to extract plant sap; some are parasitic while others are predators that feed on small invertebrates. They live in a wide variety of habitats terrestrial, though some species are adapted to life in or on the surface of fresh water. Hemipterans are hemimetabolous, with young nymphs. Many aphids are capable of parthenogenesis, producing young from unfertilised eggs. Humans have interacted with the Hemiptera for millennia; some species, including many aphids, are important agricultural pests, damaging crops by the direct action of sucking sap, but harming them indirectly by being the vectors of serious viral diseases.
Other species have been used for biological control of insect pests. Hemipterans have been cultivated for shellac; the bed bug is a persistent parasite of humans. Cicadas have been used as food, have appeared in literature from the Iliad in Ancient Greece. Hemiptera is the largest order of hemimetabolous insects containing over 75,000 named species; the group is diverse. The majority of species are terrestrial, including a number of important agricultural pests, but some are found in freshwater habitats; these include the water boatmen, pond skaters, giant water bugs. The fossil record of hemipterans goes back to the Carboniferous; the oldest fossils are of the Archescytinidae from the Lower Permian and are thought to be basal to the Auchenorrhyncha. Fulguromorpha and Cicadomorpha appear in the Upper Permian, as do Sternorrhyncha of the Psylloidea and Aleurodoidea. Aphids and Coccoids appear in the Triassic; the Coleorrhyncha extend back to the Lower Jurassic. The Heteroptera first appeared in the Triassic.
The present members of the order Hemiptera were placed into two orders, the so-called Homoptera and Heteroptera/Hemiptera, based on differences in wing structure and the position of the rostrum. The order is now divided into four or more suborders, after the "Homoptera" were established as paraphyletic; the cladogram is based on one analysis of the phylogeny of the Paraneoptera by Hu Li and colleagues in 2015, using mitochondrial genome sequences and homogeneous models. It places the Sternorrhyncha as sister clade to the Thysanoptera and the lice, making the Hemiptera as traditionally understood non-monophyletic. However, when heterogeneous models were used, Hemiptera was found to be monophyletic; the result where Hemiptera was found to be non-monophyletic is due to phylogenetic artifacts, such as elevated substitution rates in Sternorrhyncha compared with the other suborders of Hemiptera. English names are given in parentheses where possible; the defining feature of hemipterans is their "beak" in which the modified mandibles and maxillae form a "stylet", sheathed within a modified labium.
The stylet is capable of sucking liquids, while the labium supports it. The stylet contains a channel for the outward movement of saliva and another for the inward movement of liquid food. A salivary pump drives saliva into the prey. Both pumps are powered by substantial dilator muscles in the head; the beak is folded under the body when not in use. The diet is plant sap, but some hemipterans such as assassin bugs are blood-suckers, a few are predators. Both herbivorous and predatory hemipterans inject enzymes to begin digestion extraorally; these enzymes include amylase to hydrolyse starch, polygalacturonase to weaken the tough cell walls of plants, proteinases to break down proteins. Although the Hemiptera vary in their overall form, their mouthparts form a distinctive "rostrum". Other insect orders with mouthparts modified into anything like the rostrum and stylets of the Hemiptera include some Phthiraptera, but for other reasons they are easy to recognize as non-hemipteran; the mouthparts of Siphonaptera, some Diptera and Thysanoptera superficially resemble the rostrum of the Hemiptera, but on closer inspection the differences are considerable.
Aside from the mouthparts, various other insects can be confused with Hemiptera, but they all have biting mandibles and maxillae instead of the rostrum. Examples include cockroaches and psocids, both of which have longer, many-segmented antennae, some beetles, but these have hardened forewings which do not overlap; the forewings of Hemiptera are either membranous, as in the Sternorrhyncha and Auchenorrhyncha, or hardened, as in most Heteroptera. The name "Hemiptera" is from the Greek ἡμι- and πτερόν, referring to the forewings of many heteropterans which are ha
Hammerhead shark
The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a cephalofoil. Most hammerhead species are placed in the genus Sphyrna, while the winghead shark is placed in its own genus, Eusphyra. Many, but not mutually exclusive, functions have been postulated for the cephalofoil, including sensory reception and prey manipulation. Hammerheads are found worldwide in warmer waters along continental shelves. Unlike most sharks, hammerheads swim in schools during the day, becoming solitary hunters at night; some of these schools can be found near Malpelo Island in Colombia, the Galapagos Islands in Ecuador, Cocos Island off Costa Rica, near Molokai in Hawaii. Large schools are seen in the waters off southern and eastern Africa; the known species weigh from 3 to 580 kg. They are light gray and have a greenish tint, their bellies are white, which allows them to blend into the ocean when viewed from the bottom and sneak up on their prey.
Their heads have lateral projections. Hammerheads have disproportionately small mouths, they are known to form schools during the day, sometimes in groups over 100. In the evening, like other sharks, they become solitary hunters. National Geographic explains that hammerheads can be found in warm tropical waters, but during the summer, they participate in a mass migration to search for cooler waters. Since sharks do not have mineralized bones and fossilize, their teeth alone are found as fossils; the hammerheads seem related to the carcharhinid sharks that evolved during the mid-Tertiary period. According to DNA studies, the ancestor of the hammerheads lived in the Miocene epoch about 20 million years ago. Using mitochondrial DNA, a phylogenetic tree of the hammerhead sharks showed the winghead shark as its most basal member; as the winghead shark has proportionately the largest "hammer" of the hammerhead sharks, this suggests that the first ancestral hammerhead sharks had large hammers. Fossils show.
A theory has been advanced that the hammer-like shape of the head may have evolved to enhance the animal's vision. The positioning of the eyes, mounted on the sides of the shark's distinctive hammer head, allows 360° of vision in the vertical plane, meaning the animals can see above and below them at all times; the shape of the head was thought to help the shark find food, aiding in close-quarters maneuverability, allowing sharp turning movement without losing stability. However, the unusual structure of its vertebrae has been found to be instrumental in making the turns more than the shape of its head, though it would shift and provide lift. From what is known about the winghead shark, the shape of the hammerhead has to do with an evolved sensory function. Like all sharks, hammerheads have electroreceptory sensory pores called ampullae of Lorenzini; the pores on the shark's head lead to sensory tubes, which detect electricity given off by other living creatures. By distributing the receptors over a wider area, like a larger radio antenna, hammerheads can sweep for prey more effectively.
Reproduction occurs only once a year for hammerhead sharks, occurs with the male shark biting the female shark violently until she agrees to mate with him. The hammerhead sharks exhibit a viviparous mode of reproduction with females giving birth to live young. Like other sharks, fertilization is internal, with the male transferring sperm to the female through one of two intromittent organs called claspers; the developing embryos are at first sustained by a yolk sac. When the supply of yolk is exhausted, the depleted yolk sac transforms into a structure analogous to a mammalian placenta, through which the mother delivers sustenance until birth. Once the baby sharks are born, they are not taken care of by the parents in any way. A litter consists of 12 to 15 pups, except for the great hammerhead, which gives birth to litters of 20 to 40 pups; these baby sharks huddle together and swim toward warmer water until they are old enough and large enough to survive on their own. In 2007, the bonnethead shark was found to be capable of asexual reproduction via automictic parthenogenesis, in which a female's ovum fuses with a polar body to form a zygote without the need for a male.
This was the first shark known to do this. Hammerhead sharks are known to eat a large range of prey such as fish, squid and crustaceans. Stingrays are a particular favorite; these sharks are found swimming along the bottom of the ocean, stalking their prey. Their unique heads are used as a weapon; the hammerhead shark uses its head to pin down stingrays and eats the ray when the ray is weak and in shock. The great hammerhead, tending to be larger and more aggressive than most hammerheads engages in cannibalism, eating other hammerhead sharks, including its own young. In addition to the typical animal prey, bonnetheads have been found to feed on seagrass, which sometimes makes up as much as half their stomach contents, they may swallow it unintentionally, but they are able to digest it. This is the only known case of a omnivorous species of shark. According to the International Shark Attack File, humans have been subject to 17 documented, unprovoked attacks by hammerhead sharks within the genus Sphyrna since 1580 AD.
No human fatalities have been recor
Narwhal
The narwhal, or narwhale, is a medium-sized toothed whale that possesses a large "tusk" from a protruding canine tooth. It lives year-round in the Arctic waters around Greenland and Russia, it is one of two living species of whale in the Monodontidae family, along with the beluga whale. The narwhal males are distinguished by a long, helical tusk, an elongated upper left canine; the narwhal was one of many species described by Carl Linnaeus in his publication Systema Naturae in 1758. Like the beluga, narwhals are medium-sized whales. For both sexes, excluding the male's tusk, the total body size can range from 3.95 to 5.5 m. The average weight of an adult narwhal is 800 to 1,600 kg. At around 11 to 13 years old, the males become sexually mature. Narwhals do not have a dorsal fin, their neck vertebrae are jointed like those of most other mammals, not fused as in dolphins and most whales. Found in Canadian Arctic and Greenlandic and Russian waters, the narwhal is a uniquely specialized Arctic predator.
In winter, it feeds on benthic prey flatfish, under dense pack ice. During the summer, narwhals eat Arctic cod and Greenland halibut, with other fish such as polar cod making up the remainder of their diet; each year, they migrate from bays into the ocean. In the winter, the male narwhals dive up to 1,500 m in depth, with dives lasting up to 25 minutes. Narwhals, like most toothed whales, communicate with "clicks", "whistles", "knocks". Narwhals can live up to 50 years, they are killed by suffocation when the sea ice freezes over. Other causes of death among young whales, are starvation and predation by orcas; as previous estimates of the world narwhal population were below 50,000, narwhals are categorized by the International Union for Conservation of Nature as Nearly Threatened. More recent estimates list higher populations, thus lowering the status to Least Concern. Narwhals have been harvested for hundreds of years by Inuit people in northern Canada and Greenland for meat and ivory, a regulated subsistence hunt continues.
The narwhal was one of the many species described by Linnaeus in his Systema Naturae. Its name is derived from the Old Norse word nár, meaning "corpse", in reference to the animal's greyish, mottled pigmentation, like that of a drowned sailor and its summer-time habit of lying still at or near the surface of the sea; the scientific name, Monodon monoceros, is derived from the Greek: "one-tooth one-horn". The narwhal is most related to the beluga whale. Together, these two species comprise the only extant members of the family Monodontidae, sometimes referred to as the "white whales"; the Monodontidae are distinguished by medium size, forehead melons, short snouts, the absence of a true dorsal fin. Although the narwhal and the beluga are classified as separate genera, with one species each, there is some evidence that they may rarely, interbreed; the complete skull of an anomalous whale was discovered in West Greenland circa 1990. It was described by marine zoologists as unlike any known species, but with features midway between a narwhal and a beluga, consistent with the hypothesis that the anomalous whale was a narwhal-beluga hybrid.
The white whales and porpoises together comprise the superfamily Delphinoidea, which are of monophyletic origin. Genetic evidence suggests the porpoises are more related to the white whales, that these two families constitute a separate clade which diverged from the rest of Delphinoidea within the past 11 million years. Fossil evidence shows, they may have migrated to Arctic and sub-Arctic waters in response to changes in the marine food chain during the Pliocene. Narwhals are medium-sized whales, are around the same size as beluga whales. Total length in both sexes, excluding the tusk of the male, can range from 3.95 to 5.5 m. Males, at an average length of 4.1 m, are larger than females, with an average length of 3.5 m. Typical adult body weight ranges from 800 to 1,600 kg. Male narwhals attain sexual maturity at 11 to 13 years of age. Females become sexually mature at a younger age, between 5 and 8 years old, when they are around 3.4 m long. The pigmentation of narwhals is a mottled pattern, with blackish-brown markings over a white background.
They are darkest when become whiter with age. Old males may be pure white. Narwhals do not have a dorsal fin an evolutionary adaptation to swimming under ice, their neck vertebrae are jointed, like those of land mammals, instead of being fused together as in most whales. Both these characteristics are shared by the beluga whale; the tail flukes of female narwhals have front edges that are swept back, those of males have front edges that are more concave and lack a sweep-back. This is thought to be an adaptation for reducing drag caused by the tusk; the most conspicuous characteristic of the male narwhal is a single long tusk, a canine tooth that projects from the left side of the upper jaw, through the lip, forms a left-handed helix spiral. A tusk grows throughout life, it weighs around 10 kg. About one in 500 males has two tusks, occurring when the right canine grows ou
Serration
Serration refers to a saw-like appearance or a row of sharp or tooth-like projections. A serrated cutting edge has many small points of contact with the material being cut. By having less contact area than a smooth blade or other edge, the applied pressure at each point of contact is greater and the points of contact are at a sharper angle to the material being cut; this causes a cutting action that involves many small splits in the surface of the material being cut, which cumulatively serve to cut the material along the line of the blade. In nature, serration is seen in the cutting edge on the teeth of some species sharks. However, it appears on non-cutting surfaces, for example in botany where a toothed leaf margin or other plant part, such as the edge of a carnation petal, is described as being serrated. A serrated leaf edge may reduce the force of wind and other natural elements; the largest serrations on Earth occur on the skylines of mountains. These occur both due to the uneven action of landform edges pushing rock upwards, the uneven action of erosion.
Human uses of serration have copied, gone beyond, those found in nature. For example, the teeth on a saw or other serrated blade serves a similar cutting or scraping purpose as the serration of an animal tooth. Tailors use pinking shears to cut cloth with a serrated edge, somewhat counterintuitively, reduces fraying by reducing the average length of a thread that may be pulled from the edge. A type of serration is found in airframe shapes used in certain stealth aircraft, which use the jaggedness of the serrated edge to deflect radar signals from seams and edges where a straight, non-serrated edge would reflect radar signals back to the source. Screw threads show serration in profile, although they are shown in abbreviated or symbolic fashion on mechanical drawings to save time and ink. Brogue shoes are made with serrated edges on the leather pieces, for no known purpose at all other than style; the step clamp and step block assembly in metalworking adopt serration for the purpose of applying clamping pressure from an adjustable position
Carapace
A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods, such as crustaceans and arachnids, as well as vertebrates, such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron. In crustaceans, the carapace functions as a protective cover over the cephalothorax. Where it projects forward beyond the eyes, this projection is called a rostrum; the carapace is calcified to varying degrees in different crustaceans. Zooplankton within the phylum Crustacea have a carapace; these include Cladocera and isopods, but isopods only have a developed "cephalic shield" carapace covering the head. In arachnids, the carapace is formed by the fusion of prosomal tergites into a single plate which carries the eyes, ocularium and diverse phaneres. In a few orders, such as Solifugae and Schizomida, the carapace may be subdivided. In Opiliones, some authors prefer to use the term carapace interchangeably with the term cephalothorax, incorrect usage, because carapace refers only to the dorsal part of the exoskeleton of the cephalothorax.
Alternative terms for the carapace of arachnids and their relatives, which avoids confusion with crustaceans, are prosomal dorsal shield and peltidium. The carapace is the dorsal convex part of the shell structure of a turtle, consisting of the animal's rib cage, dermal armor, scutes
Fish jaw
Most bony fishes have two sets of jaws made of bone. The primary oral jaws open and close the mouth, a second set of pharyngeal jaws are positioned at the back of the throat; the oral jaws are used to manipulate prey by biting and crushing. The pharyngeal jaws, so-called because they are positioned within the pharynx, are used to further process the food and move it from the mouth to the stomach. Cartilaginous fishes, such as sharks and rays, have one set of oral jaws made of cartilage, they do not have pharyngeal jaws. Jaws are articulated and oppose vertically, comprising an upper jaw and a lower jaw and can bear numerous ordered teeth. Cartilaginous fishes grow multiple sets and replace teeth as they wear by moving new teeth laterally from the medial jaw surface in a conveyor-belt fashion. Teeth are replaced multiple times in most bony fishes, but unlike cartilaginous fishes, the new tooth erupts only after the old one has fallen out. Jaws originated in the pharyngeal arches supporting the gills of jawless fish.
The earliest jaws appeared is now extinct placoderms and spiny sharks during the Silurian, about 430 million years ago. The original selective advantage offered by the jaw was not related to feeding, but to increased respiration efficiency—the jaws were used in the buccal pump to pump water across the gills; the familiar use of jaws for feeding would have developed as a secondary function before becoming the primary function in many vertebrates. All vertebrate jaws, including the human jaw, evolved from early fish jaws; the appearance of the early vertebrate jaw has been described as "perhaps the most profound and radical evolutionary step in the vertebrate history". Fish without jaws had more difficulty surviving than fish with jaws, most jawless fish became extinct. Jaws use linkage mechanisms; these linkages can be common and complex in the head of bony fishes, such as wrasses, which have evolved many specialized feeding mechanisms. Advanced are the linkage mechanisms of jaw protrusion. For suction feeding a system of linked four-bar linkages is responsible for the coordinated opening of the mouth and the three-dimensional expansion of the buccal cavity.
Other linkages are responsible for protrusion of the premaxilla. Linkage systems are distributed in animals; the most thorough overview of the different types of linkages in animals has been provided by M. Muller, who designed a new classification system, well suited for biological systems; the skull of fishes is formed from a series of loosely connected bones. Lampreys and sharks only possess a cartilaginous endocranium, with both the upper and lower jaws being separate elements. Bony fishes have additional dermal bone, forming a more or less coherent skull roof in lungfish and holost fish; the lower jaw defines a chin. The simpler structure is found in jawless fish, in which the cranium is represented by a trough-like basket of cartilaginous elements only enclosing the brain, associated with the capsules for the inner ears and the single nostril. Distinctively, these fish have no jaws. Cartilaginous fish, such as sharks have simple skulls; the cranium is a single structure forming a case around the brain, enclosing the lower surface and the sides, but always at least open at the top as a large fontanelle.
The most anterior part of the cranium includes a forward plate of cartilage, the rostrum, capsules to enclose the olfactory organs. Behind these are the orbits, an additional pair of capsules enclosing the structure of the inner ear; the skull tapers towards the rear, where the foramen magnum lies above a single condyle, articulating with the first vertebra. There are, in addition, at various points throughout the cranium, smaller foramina for the cranial nerves; the jaws consist of separate hoops of cartilage always distinct from the cranium proper. In ray-finned fishes, there has been considerable modification from the primitive pattern; the roof of the skull is well formed, although the exact relationship of its bones to those of tetrapods is unclear, they are given similar names for convenience. Other elements of the skull, may be reduced; the upper jaw is formed from the premaxilla, with the maxilla itself located further back, an additional bone, the symplectic, linking the jaw to the rest of the cranium.
Although the skulls of fossil lobe-finned fish resemble those of the early tetrapods, the same cannot be said of those of the living lungfishes. The skull roof is not formed, consists of multiple, somewhat irregularly shaped bones with no direct relationship to those of tetrapods; the upper jaw is formed from the vomers alone, all of which bear teeth. Much of the skull is formed from cartilage, its overall structure is reduced. In vertebrates, the lower jaw is a bone forming the skull with the cranium. In lobe-finned fishes and the early fossil tetrapods, the bone homologous to the mandible of mammals is the largest of several bones in the lower jaw, it is referred to as the dentary bone, forms the body of the outer surface of the jaw. It is bordered below by a number of splenial bones, while the angle of the jaw is formed by a lower angular bone and a suprangular bone just above it; the inner surface of the jaw is lined by a prearticular bone, while the articular bone forms the articulation with the skull proper.
A set of three narrow coronoid bones lie above the prearticular bone. As the name implies, the majority of the teeth are attached to the dentary, but there are also teet
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