what is a segmented body in insects

[8] Pumping movements of the body force the air through the system. [1]:2224 Insects are the only invertebrates to have developed flight capability, and this has played an important part in their success. In addition, in Orthoptera and Blattodea, the anal area is folded like a fan along the veins, the anal veins being convex, at the crests of the folds, and the accessory veins concave. Air enters a series of tubes along the body through openings called spiracles, and is then taken into increasingly finer fibers. [8], The genitalia of female flies are rotated to a varying degree from the position found in other insects. Distally, the vannal veins are either simple or branched. In the exoporian type (in Hepialoidea and Mnesarchaeoidea) there are two separate places for insemination and oviposition, both occurring on the same sterna as the monotrysian type, 9/10. Species of the genus Anopheles are characterized by their long palpi (two parts with widening end), almost reaching the end of labrum. [38], All the veins of the wing are subject to secondary forking and union by cross-veins. [1]:2248 Although the general function of the three body regions is the same across all insect species, there are major differences in basic structure, with wings, legs, antennae, and mouthparts being variable from group to group.[3]. [38]:165166, For the most part, the femur and tibia are the longest leg segments but variations in the lengths and robustness of each segment relate to their functions. Each of the wings consists of a thin membrane supported by a system of veins. The remaining areas form channels, the future veins, in which the nerves and tracheae may occur. After there is a midgut, that varies in dimensions between species, with a large amount of cecum, with a hingut, with varying lengths. [7] In the anatomy of some taxa, such as many Cicadomorpha, the front of the head is fairly clearly distinguished and tends to be broad and sub-vertical; that median area commonly is taken to be the frons. In most species the genitalia are flanked by two soft lobes, although they may be specialized and sclerotized in some species for ovipositing in area such as crevices and inside plant tissue. Oxygen is obtained via a tracheal system. Gas exchange patterns in insects can range from continuous and diffusive ventilation, to discontinuous gas exchange. Segments 8 and 9 bear the genitalia; segment 10 is visible as a complete segment in many "lower" insects but always lacks appendages. Insects also have been used in biochemical, developmental, behavioral, environmental, and ecological studies. When the new cuticle has formed sufficiently, the epicuticle and reduced exocuticle are shed in ecdysis. Depending on the insect, the suture may come in different shapes: like either a Y, U or V. Those diverging lines that make up the ecdysial suture are called the frontal or frontogenal sutures. The foregut includes the buccal cavity (mouth), pharynx, esophagus, and Crop and proventriculus (any part may be highly modified), which both store food and signify when to continue passing onward to the midgut. The meron reaches the extreme of its departure from the usual condition in the Diptera. In the flexed wing, the outer squama of the alula is turned upside down above the inner squama, the latter not being affected by the movement of the wing. This article was most recently revised and updated by, https://www.britannica.com/science/entomology, entomology - Student Encyclopedia (Ages 11 and up). The ducts and spermathecae are lined with a cuticle. The arthropod body consists of three segments with a hard exoskeleton and jointed appendages. [26], The typical and usual segments of the insect leg are divided into the coxa, one trochanter, the femur, the tibia, the tarsus, and the pretarsus. An air bubble provides an insect with only a short-term supply of oxygen, but thanks to its unique physical properties, oxygen will diffuse into the bubble and displacing the nitrogen, called passive diffusion, however the volume of the bubble eventually diminishes, and the beetle will have to return to the surface.[70]. This article focuses on the segmentation of animal body plans, specifically using the examples of the taxa Arthropoda, Chordata, and Annelida. [9], The clypeus is a sclerite between the face and labrum, which is dorsally separated from the frons by the frontoclypeal suture in primitive insects. Toward the thorax, the dorsal tube (element 14) divides into chambers and acts like the insect's heart. The phylum also includes spiders, centipedes, and crustaceans. The ejaculatory duct is derived from an invagination of the epidermal cells during development and, as a result, has a cuticular lining. In bull ants, the mandibles are elongated and toothed, used as hunting (and defensive) appendages. The proximal plate (m) is usually attached to the distal arm of the third axillary and perhaps should be regarded as a part of the latter. The larvae reacted to the touch of the heated probe with a stereotypical rolling behavior that was not exhibited when the larvae were touched by the unheated probe. The first section of the alimentary canal is the foregut (element 27 in numbered diagram), or stomodaeum. [10], On the posterior aspect of the head are the occiput, postgena, occipital foramen, posterior tentorial pit, gula, postgenal bridge, hypostomal suture and bridge, and the mandibles, labium, and maxilla. These modifications allow insects to occupy almost every ecological niche except the deep ocean. Most phylogenetically advanced insects have two pairs of wings located on the second and third thoracic segments. It is hinged to the clypeus. Get a Britannica Premium subscription and gain access to exclusive content. And finally, the labrum (upper lip) is used to suck up the blood. Three parts of an insect: head, thorax, abdomen. In the order Coleoptera, tympanal organs have been described in at least two families. The base of the triangle (a-b) is the hinge of the wing with the body; the apex (c) is the distal end of the third axillary sclerite; the longer side is anterior to the apex. Laterally it is limited by the fronto-genal sulcus, if present, and the boundary with the vertex, by the ecdysial cleavage line, if it is visible. Some colonies of social insects, such as tropical termites and ants, may reach populations of millions of inhabitants. [1][59], Body fluids enter through one-way valved ostia, which are openings situated along the length of the combined aorta and heart organ. [1]:49 The small segment 11 may be represented by an epiproct (usually a dorsal plate or filament above the anus of certain insects); other appendages include: The nervous system of an insect can be divided into a brain and a ventral nerve cord. [62][63], Cockroaches are most common in tropical and subtropical climates. This forces the male to lie on its back in order for its genitalia to remain engaged with those of the female, or the torsion of the male genitals allows the male to mate while remaining upright. Insects, Spiders, Centipedes, Millipedes - U.S. National Park Service Salivary secretions from the labella assist in dissolving and collecting food particles so they can be more easily taken up by the pseudotracheae or laid their egg on the suitable media; this is thought to occur by capillary action. In the cicada, the vannal fold lies immediately behind the first vannal vein (lV). The majority of insect material is inside of the endocuticle. These structures usually reside in the thorax, adjacent to the foregut. In discontinuous gas exchange, however, the insect takes in oxygen while it is active and small amounts of carbon dioxide are released when the insect is at rest. It is based on a combination of speculation and fossil data. When the veins of this region are distinct at their bases, they are associated with the outer median plate. In the hindwings of most Orthoptera, a secondary vena dividens forms a rib in the vannal fold. The terminalia of adult female insects include internal structures for receiving the male copulatory organ and his spermatozoa and external structures used for oviposition (egg-laying; section 5.8). Compound eyes fall into two groups: apposition eyes, which form multiple inverted images, and superposition eyes, which form a single erect image. The anal veins are articulated with this sclerite in such a way that when it moves they are carried with it and become flexed over the back of the insect. On the under surfaces of the tarsal subsegments in certain Orthoptera, there are small pads, the tarsal pulvilli, or euplantulae. [38], The fifth vein of the wing is the media. A more formal definition is that it is the sclerite from which the pharyngeal dilator muscles arise, but in many contexts that too, is not helpful. The vannal region is usually best developed in the hindwing, in which it may be enlarged to form a sustaining surface, as in Plecoptera and Orthoptera. Muscles arising on the frons are inserted into these sclerites, which distally are hinged to a pair of lingual sclerites. Its form is highly variable and often irregular, but the third axillary is the sclerite on which is inserted the flexor muscle of the wing (D). The French biologist Ren-Antoine Ferchault de Raumur published the first of six volumes of Mmoires pour servir lhistoire des insectes (Memoirs Serving as a History of Insects) in 1734. The base of the aedeagus may be the partially sclerotized phallotheca, also called the phallosoma or theca. [47][48] Most of this food is ingested in the form of macromolecules and other complex substances like proteins, polysaccharides, fats, and nucleic acids. The cuticle provides muscular support and acts as a protective shield as the insect develops. In almost all extant insects,[1]:4142 the precosta is fused with the costa; the costa rarely ever branches because it is at the leading edge, which is associated at its base with the humeral plate. The usual single trochanteral segment of insects, therefore, probably represents the two trochanters of other arthropods fused into one apparent segment since it is not likely that the primary coxotrochanteral hinge has been lost from the leg. [38]:164, The trochanter is the basal segment of the telopodite; it is always a small segment in the insect leg, freely movable by a horizontal hinge on the coxa, but more or less fixed to the base of the femur. The cheek or gena forms the sclerotized area on each side of the head below the compound eyes extending to the gular suture. They lie in the median area of the wing base distal to the second and third axillaries and are separated from each other by an oblique line (bf), which forms a prominent convex fold during flexion of the wing. [22] The general shape of the antennae is also quite variable, but the first segment (the one attached to the head) is always called the scape, and the second segment is called the pedicel. [40] Similarly, protibia, mesotibia, and metatibia refer to the tibiae of the front, middle and hind legs. This can only be countered by increasing lens size and number. [32] They are conspicuous and five-segmented in some of the more basal families and are often folded. Language links are at the top of the page across from the title. In Brachycera, the labellum is especially prominent and used for sponging liquid or semiliquid food. The trachea of the costal vein is perhaps a branch of the subcostal trachea. [38], The postcubitus (Pcu) is the first anal of the Comstock and Needham system. [39] The veins of the wing appear to fall into an undulating pattern according to whether they tend to fold up or down when the wing is relaxed. The muscles of the cibarium or pharynx are strongly developed to form a pump. The body of knowledge gleaned from the study of insects has enabled modern economic entomologists to develop a wide range of methods for controlling insect pests. Spiracles, the external organs of the respiratory system, are found on the pterothorax, usually one between the pro- and mesopleoron, as well as one between the meso- and metapleuron. Toward the middle of the wing, it forks into a first undivided branch (R1) and a second branch, called the radial sector (Ra), which subdivides dichotomously into four distal branches (R2, R3, R4, R5). These chemicals mix and result in an explosive ejection, forming temperatures of around 100 C, with the breakdown of hydroquinone to H2 + O2 + quinone, with the O2 propelling the excretion. The first three pairs of ganglia are fused into the brain, while the three following pairs are fused into a structure of three pairs of ganglia under the insect's esophagus, called the subesophageal ganglion. This lack of features is an adaptation to a food-rich environment, such as within rotting organic matter, or as an endoparasite. [38]:165, The femur is the third segment of the insect leg, is usually the longest and strongest part of the limb, but it varies in size from the huge hind femur of leaping Orthoptera to a very small segment such as is present in many larval forms. The meron may be greatly enlarged by an extension distally in the posterior wall of the coxa; in the Neuroptera, Mecoptera, Trichoptera, and Lepidoptera, the meron is so large that the coxa appears to be divided into an anterior piece, the so-called "coxa genuina," and the meron, but the meron never includes the region of the posterior trochanteral articulation, and the groove delimiting it is always a part of the basicostal suture. The concave vein will fork into two concave veins (with the interpolated vein being convex) and the regular alteration of the veins is preserved. [49] In addition to the alimentary canal, insects also have paired salivary glands and salivary reservoirs. To see with a resolution comparable to our simple eyes, humans would require compound eyes that would each reach the size of their heads. They dominate the present-day land fauna with about 1 million described species. [1]:2224, The insect thorax has three segments: the prothorax, mesothorax, and metathorax. While cockroaches do not have lungs and thus do not actively breathe in the vertebrate lung manner, in some very large species the body musculature may contract rhythmically to forcibly move air out and in the spiracles; this may be considered a form of breathing. In most modern insects, the media anterior has been lost, and the usual "media" is the four-branched media posterior with the common basal stem. Three physical features separate insects from other arthropods: they have a body divided into three regions (called tagmata) (head, thorax, and abdomen), three pairs of legs, and mouthparts located outside of the head capsule. [8] The shape and dimensions of the proboscis have evolved to give different species wider and therefore more advantageous diets. In the mature wings of more generalized insects, the postcubitus is always associated proximally with the cubitus and is never intimately connected with the flexor sclerite (3Ax) of the wing base. In the 4th century bce, the Greek philosopher and scientist Aristotle provided descriptions of insect anatomy, establishing the groundwork for modern entomology. Entomology | Definition & Facts | Britannica [26] Until recently, the labrum generally was considered to be associated with the first head segment. In Elateridae species, the predatory larvae defecate enzymes on their prey, with digestion being extraorally. [2] The head is specialized for sensory input and food intake; the thorax, which is the anchor point for the legs and wings (if present), is specialized for locomotion; and the abdomen is for digestion, respiration, excretion, and reproduction. Since oxygen is delivered directly, the circulatory system is not used to carry oxygen, and is therefore greatly reduced. They write new content and verify and edit content received from contributors. The proximal part of the maxilla consists of a basal cardo, which has a single articulation with the head, and a flat plate, the stipes, hinged to the cardo. In prognathous insects, the vertex is not found between the compound eyes, but rather where the ocelli are normally found. The four different fields found on insect wings are: Most veins and cross-veins occur in the anterior area of the remigium, which is responsible for most of the flight, powered by the thoracic muscles. The lateral ducts are where the eggs leave the body, while the spermatheca is where sperm is stored. The more constant cross-veins are the humeral cross-vein (h) between the costa and subcosta, the radial cross-vein (r) between R and the first fork of Rs, the sectorial cross-vein (s) between the two forks of R8, the median cross-vein (m-m) between M2 and M3, and the mediocubital cross-vein (m-cu) between the media and the cubitus. In such cases, the coxa appears to be divided into two parts corresponding to the episternum and epimeron of the pleuron. This break-down process is known as digestion. [38], The various movements of the wings, especially in insects that flex their wings horizontally over their backs when at rest, demand a more complicated articular structure at the wing base than a mere hinge of the wing with the body. [8], The reproductive system of females consist of paired ovaries, lateral oviducts, spermatheca, and a genital chamber. After emerging from the pupa, the adult fly rarely lives more than a few days, and serves mainly to reproduce and to disperse in search of new food sources. Some species are in close association with human dwellings and widely found around garbage or in the kitchen. In nymphal wings, its trachea arises between the cubital trachea and the group of vannal tracheae. They also have palps, which are used to sense the characteristics of potential foods. The alula is well developed in the house fly. An "arthropod" is an invertebrate animal that has an exoskeleton, a segmented body, and jointed appendages. The occipital arch is a narrow band forming the posterior edge of the head capsule arching dorsally over the foramen. In pterygotes, the postocciput forms the extreme posterior, often U-shaped, which forms the rim of the head extending to the postoccipital suture. Author of. Of all the insect orders, Orthoptera displays the greatest variety of features found in the heads of insects, including the sutures and sclerites. A coxa with an enlarged meron has an appearance similar to one divided by a coxal suture falling in line with the pleural suture, but the two conditions are fundamentally quite different and should not be confused. [44] This was discovered in 2003 by studying the variation in reactions of larvae of the common fruitfly Drosophila to the touch of a heated probe and an unheated one. [1]:4142 Interaction between the pupal brain and prothoracic glands in the metamorphosis of the giant silkworm "Platysamia cecropia", "A temperature-induced switch from diffusive to convective ventilation in the honeybee", https://en.wikipedia.org/w/index.php?title=Insect_morphology&oldid=1162556282, Articles with dead external links from November 2017, Articles with permanently dead external links, Short description is different from Wikidata, Creative Commons Attribution-ShareAlike License 4.0, The anal-genital part of the abdomen. [26]:45, The ground plan of the abdomen of an adult insect typically consists of 1112 segments and is less strongly sclerotized than the head or thorax. There are typically four to six Malpighian tubules. The insect's outer skeleton, the cuticle, consists of two layers; the epicuticle, which is a thin, waxy, water-resistant outer layer that lacks chitin, and the layer under it is called the procuticle. The fourth axillary sclerite is not a constant element of the wing base. [31] While Bombardier beetles have well developed, like other carabid beetles, pygidial glands that empty from the lateral edges of the intersegment membranes between the seventh and eighth abdominal segments. Updates? In the flexed wing, the remigium turns posteriorly on the flexible basal connection of the radius with the second axillary, and the base of the mediocubital field is folded medially on the axillary region along the plica basalis (bf) between the median plates (m, m') of the wing base. From there, the pharynx passes food to the esophagus, which could be just a simple tube passing it on to the crop and proventriculus, and then on ward to the midgut, as in most insects. [1]:6568 During continuous gas exchange, oxygen is taken in and carbon dioxide is released in a continuous cycle. [38], The auxiliary region containing the axillary sclerites has, in general, the form of a scalene triangle. The cuticle surrounding the veins becomes thickened and more heavily sclerotized to provide strength and rigidity to the wing. [52], In the hindgut (element 16 in numbered diagram), or proctodaeum, undigested food particles are joined by uric acid to form fecal pellets. For example, gressorial and cursorial, or walking and running type insects respectively, usually have well-developed femora and tibiae on all legs, whereas jumping (saltatorial) insects such as grasshoppers have disproportionately developed metafemora and metatibiae. Spiracles are located in the pleural area. Where found, the occipital suture is the arched, horseshoe-shaped groove on the back of the head ending at the posterior of each mandible. The third, the posterior, thoracic segment, abutting the abdomen, is the metathorax, which bears the third pair of legs and the posterior wings. This is formed from the fusion of parts of a pair of ancestral appendages found on the third head segment, showing their relationship. Point d on the anterior side of the triangle marks the articulation of the radial vein with the second axillary sclerite. Behaviour is diverse, from the almost inert parasitic forms, whose larvae lie in the nutrient bloodstreams of their hosts and feed by absorption, to dragonflies that pursue victims in the air, tiger beetles that outrun prey on land, and predaceous water beetles that outswim prey in water. In most of the higher insects with narrow wings, the vannus becomes reduced, and the vannal fold is lost, but even in such cases, the flexed wing may bend along a line between the postcubitus and the first vannal vein. The dorsal tracheae supply oxygen to the dorsal musculature and vessels, while the ventral tracheae supply the ventral musculature and nerve cord, and the visceral tracheae supply the guts, fat bodies, and gonads. Evolution solved this problem with In some, such as the twisted-wing insects (Strepsiptera), the female is a mere inactive bag of eggs, and the winged male is one of the most active insects known. Both cardo and stipes are loosely joined to the head by a membrane, so they are capable of movement. The fourth vein is the radius, which is branched into five separate veins. In feeding, the tongue is dipped into the nectar or honey, which adheres to the hairs, and then is retracted so the adhering liquid is carried into the space between the galeae and labial palps. [41], The tarsus of insects corresponds to the penultimate segment of a generalized arthropod limb, which is the segment called the propodite in Crustacea. In meroistic ovaries, the eggs-to-be divide repeatedly and most of the daughter cells become helper cells for a single oocyte in the cluster. The tarsus is occasionally fused with the tibia in larval insects, forming a tibiotarsal segment; in some cases, it appears to be eliminated or reduced to a rudiment between the tibia and the pretarsus. Studies using the vinegar fly (Drosophila melanogaster) have established the foundation and techniques used in virtually all aspects of genetics research conducted today. Some insects are perceived as threats to humans, both as agents of crop destruction and as disseminators of disease. Insects have six segmented legs, which take many different forms depending on their function. Hairs of two types may occur on the wings: microtrichia, which are small and irregularly scattered, and macrotrichia, which are larger, socketed, and may be restricted to veins. It can contain unpalatable and malodourous chemicals that will act as a deterrent to predators. The middle segment is the mesothorax; its major features are the second pair of legs and the anterior wings, if any. The third axillary, therefore, is usually the posterior hinge plate of the wing base and is the active sclerite of the flexor mechanism, which directly manipulates the vannal veins. The labium (lower lip) is the fused structure that moves longitudinally and has a pair of segmented palps. Winged aphids invade New York City. During the embryonic stage of many insects and the postembryonic stage of primitive insects, 11 abdominal segments are present. Whereas the claval furrow and jugal fold are probably homologous in different species, the vannal fold varies in position in different taxa. Though fold lines may be transverse, as in the hindwings of beetles and earwigs, they are normally radial to the base of the wing, allowing adjacent sections of a wing to be folded over or under each other. [8]:885 The aedeagus can be quite pronounced or de minimis. The mandibles are positioned between the labrum and maxillae. [1]:43, When at rest, the wings are held over the back in most insects, which may involve longitudinal folding of the wing membrane and sometimes also transverse folding. Pliny the Elder added to Aristotles list of species. The primary forking takes place near the base of the wing, forming the two principal branches (Cu1, Cu2). Updates? [26], In mandibulate mouthparts, the labium is a quadrupedal structure, although it is formed from two fused secondary maxillae. It contains all the muscles for the legs and wings, which are attached to this part of the body. [4] The difference between the unmodified and modified forms is evident when comparing the body wall of a caterpillar (unmodified) to a beetle (modified). The postoccipital suture is a landmark on the posterior surface of the head, and is typically near the occipital foremen. However, apterygotes (bristletails and silverfish) and many immature aquatic insects have abdominal appendages. The zoological categories of genetics, taxonomy, morphology, physiology, behaviour, and ecology are included in this field of study. Situated beneath the mandibles, paired maxillae manipulate food during mastication. Apterygotes possess a pair of styles; rudimentary appendages that are serially homologous with the distal part of the thoracic legs. [26] In nonbiting flies, the mandibles are absent and other structures are reduced; the labial palps have become modified to form the labellum, and the maxillary palps are present, although sometimes short. [1]:2224 The exocuticle is greatly reduced in many soft-bodied insects, especially the larval stages (e.g., caterpillars). The outer wall of the coxa is often marked by a suture extending from the base to the anterior trochanteral articulation. In the majority of the flying insects (Neoptera), it is derived from bipolar formation. The labrum is raised away from the mandibles by two muscles arising in the head and inserted medially into the anterior margin of the labrum. The coxa is attached to the body by an articular membrane, the coxal corium, which surrounds its base. The three types of occipital closures, or points under the occipital foramen that separate the two lower halves of the postgena, are the hypostomal bridge, the postgenal bridge, and the gula. The main structure of an insect's digestive system is a long-enclosed tube called the alimentary canal (or gut), which runs lengthwise through the body. How can an animal with a rigid body covering move its legs? Like other insect species, beetles have hemolymph instead of blood. Long, slender (extratory) malpighian tubules can be found between the junction of the mid- and hind gut. The gland is made of two containing chambers. The basicosta strengthens the base of the coxa and is commonly enlarged on the outer wall to give insertion to muscles; on the mesal half of the coxa, however, it is usually weak and often confluent with the coxal margin. The remaining antennal segments or flagellomeres are called the flagellum.
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