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33-423: Generally organisms with a larval stage undergo metamorphosis, and during metamorphosis the organism loses larval characteristics. The word metamorphosis derives from Ancient Greek μεταμόρφωσις , "transformation, transforming", from μετα- ( meta- ), "after" and μορφή ( morphe ), "form". In insects, growth and metamorphosis are controlled by hormones synthesized by endocrine glands near

66-498: A yolk sac ), then to motile larvae (often known as fingerlings due to them roughly reaching the length of a human finger ) that have to forage for themselves after the yolk sac resorbs, and then to the juvenile stage where the fish progressively start to resemble adult morphology and behaviors until finally reaching sexual maturity . In typical amphibian development, eggs are laid in water and larvae are adapted to an aquatic lifestyle. Frogs , toads , and newts all hatch from

99-435: A butterfly 2 – The pupa is now spewing the thread to form chrysalis 3 – The chrysalis is fully formed 4 – Adult butterfly coming out of the chrysalis In cephalochordata , metamorphosis is iodothyronine -induced and it could be an ancestral feature of all chordates . Some fish, both bony fish (Osteichthyes) and jawless fish (Agnatha) , undergo metamorphosis. Fish metamorphosis is typically under strong control by

132-647: A complete metamorphosis, including a pupal or resting stage between the larval and adult forms. A number of hypotheses have been proposed to explain the evolution of holometaboly from hemimetaboly, mostly centering on whether or not the intermediate stages of hemimetabolous forms are homologous in origin to the pupal stage of holometabolous forms. According to a 2009 study, temperature plays an important role in insect development as individual species are found to have specific thermal windows that allow them to progress through their developmental stages. These windows are not significantly affected by ecological traits, rather,

165-410: A considerable role during physiological processes of multicellular organisms, particularly during embryogenesis , and metamorphosis. Additional research in 2019 found that both autophagy and apoptosis , the two ways programmed cell death occur, are processes undergone during insect metamorphosis. Below is the sequence of steps in the metamorphosis of the butterfly (illustrated): 1 – The larva of

198-583: A distinct environment, larvae may be given shelter from predators and reduce competition for resources with the adult population. Animals in the larval stage will consume food to fuel their transition into the adult form. In some organisms like polychaetes and barnacles , adults are immobile but their larvae are mobile, and use their mobile larval form to distribute themselves. These larvae used for dispersal are either planktotrophic (feeding) or lecithotrophic (non-feeding) . Some larvae are dependent on adults to feed them. In many eusocial Hymenoptera species,

231-583: A distinct environment, larvae may be given shelter from predators and reduce competition for resources with the adult population. Animals in the larval stage will consume food to fuel their transition into the adult form. In some organisms like polychaetes and barnacles , adults are immobile but their larvae are mobile, and use their mobile larval form to distribute themselves. These larvae used for dispersal are either planktotrophic (feeding) or lecithotrophic (non-feeding) . Some larvae are dependent on adults to feed them. In many eusocial Hymenoptera species,

264-622: A larval phase of their life cycle . A larva's appearance is generally very different from the adult form ( e.g. caterpillars and butterflies ) including different unique structures and organs that do not occur in the adult form. Their diet may also be considerably different. In the case of smaller primitive arachnids, the larval stage differs by having three instead of four pairs of legs. Larvae are frequently adapted to different environments than adults. For example, some larvae such as tadpoles live almost exclusively in aquatic environments, but can live outside water as adult frogs . By living in

297-419: A more gradual metamorphosis to the migrating phase. In the pre-adult freshwater stage, the eel also has phenotypic plasticity because fish-eating eels develop very wide mandibles, making the head look blunt. Leptocephali are common, occurring in all Elopomorpha ( tarpon - and eel -like fish). Most other bony fish undergo metamorphosis initially from egg to immotile larvae known as sac fry ( fry with

330-419: A relatively long, spiral‐shaped gut to digest that diet. Recent studies suggest tadpoles do not have a balanced homeostatic feedback control system until the beginning stages of metamorphosis. At this point, their long gut shortens and begins favoring the diet of insects. Rapid changes in the body can then be observed as the lifestyle of the frog changes completely. The spiral‐shaped mouth with horny tooth ridges

363-442: Is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects , some arachnids , amphibians , or cnidarians typically have a larval phase of their life cycle . A larva's appearance is generally very different from the adult form ( e.g. caterpillars and butterflies ) including different unique structures and organs that do not occur in

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396-436: Is based on Antonio Berlese classification in 1913. There are four main types of endopterygote larvae types: Larval A larva ( / ˈ l ɑːr v ə / ; pl. : larvae / ˈ l ɑːr v iː / ) is a distinct juvenile form many animals undergo before metamorphosis into their next life stage. Animals with indirect development such as insects , some arachnids , amphibians , or cnidarians typically have

429-554: Is iodothyronine-induced and an ancestral feature of all chordates . All three categories of metamorphosis can be found in the diversity of insects, including no metamorphosis ("ametaboly"), incomplete or partial metamorphosis ("hemimetaboly"), and complete metamorphosis ("holometaboly"). While ametabolous insects show very little difference between larval and adult forms (also known as " direct development "), both hemimetabolous and holometabolous insects have significant morphological and behavioral differences between larval and adult forms,

462-421: Is outside the parental body, development is subject to many adaptations due to specific ecological circumstances. For this reason tadpoles can have horny ridges for teeth, whiskers, and fins. They also make use of the lateral line organ. After metamorphosis, these organs become redundant and will be resorbed by controlled cell death, called apoptosis . The amount of adaptation to specific ecological circumstances

495-547: Is reabsorbed, due to the higher thyroxin concentrations required for tail resorption. Salamander development is highly diverse; some species go through a dramatic reorganization when transitioning from aquatic larvae to terrestrial adults, while others, such as the axolotl , display pedomorphosis and never develop into terrestrial adults. Within the genus Ambystoma , species have evolved to be pedomorphic several times, and pedomorphosis and complete development can both occur in some species. In newts, metamorphosis occurs due to

528-402: Is remarkable, with many discoveries still being made. With frogs and toads, the external gills of the newly hatched tadpole are covered with a gill sac after a few days, and lungs are quickly formed. Front legs are formed under the gill sac, and hindlegs are visible a few days later. Following that there is usually a longer stage during which the tadpole lives off a vegetarian diet. Tadpoles use

561-401: Is resorbed together with the spiral gut. The animal develops a big jaw, and its gills disappear along with its gill sac. Eyes and legs grow quickly, a tongue is formed, and all this is accompanied by associated changes in the neural networks (development of stereoscopic vision, loss of the lateral line system, etc.) All this can happen in about a day. It is not until a few days later that the tail

594-857: Is the required hormone, and for adaptation to the land phase, thyroxin . External gills do not return in subsequent aquatic phases because these are completely absorbed upon leaving the water for the first time. Basal caecilians such as Ichthyophis go through a metamorphosis in which aquatic larva transition into fossorial adults, which involves a loss of the lateral line . More recently diverged caecilians (the Teresomata ) do not undergo an ontogenetic niche shift of this sort and are in general fossorial throughout their lives. Thus, most caecilians do not undergo an anuran-like metamorphosis. [REDACTED] The dictionary definition of metamorphosis at Wiktionary Larva A larva ( / ˈ l ɑːr v ə / ; pl. : larvae / ˈ l ɑːr v iː / )

627-401: The adult form. Their diet may also be considerably different. In the case of smaller primitive arachnids, the larval stage differs by having three instead of four pairs of legs. Larvae are frequently adapted to different environments than adults. For example, some larvae such as tadpoles live almost exclusively in aquatic environments, but can live outside water as adult frogs . By living in

660-410: The change in habitat, not a change in diet, because newt larvae already feed as predators and continue doing so as adults. Newts' gills are never covered by a gill sac and will be resorbed only just before the animal leaves the water. Adults can move faster on land than in water. Newts often have an aquatic phase in spring and summer, and a land phase in winter. For adaptation to a water phase, prolactin

693-459: The development of adult characteristics during ecdysis . In holometabolous insects, molts between larval instars have a high level of juvenile hormone, the moult to the pupal stage has a low level of juvenile hormone, and the final, or imaginal , molt has no juvenile hormone present at all. Experiments on firebugs have shown how juvenile hormone can affect the number of nymph instar stages in hemimetabolous insects. In chordates, metamorphosis

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726-538: The eggs as larvae with external gills but it will take some time for the amphibians to interact outside with pulmonary respiration. Afterwards, newt larvae start a predatory lifestyle, while tadpoles mostly scrape food off surfaces with their horny tooth ridges. Metamorphosis in amphibians is regulated by thyroxin concentration in the blood, which stimulates metamorphosis, and prolactin , which counteracts its effect. Specific events are dependent on threshold values for different tissues. Because most embryonic development

759-655: The evolution of metamorphosis in insects is thought to have fuelled their dramatic radiation (1,2). Some early ametabolous "true insects" are still present today, such as bristletails and silverfish . Hemimetabolous insects include cockroaches , grasshoppers , dragonflies , and true bugs . Phylogenetically, all insects in the Pterygota undergo a marked change in form, texture and physical appearance from immature stage to adult. These insects either have hemimetabolous development, and undergo an incomplete or partial metamorphosis, or holometabolous development, which undergo

792-410: The front of the body ( anterior ). Neurosecretory cells in an insect's brain secrete a hormone, the prothoracicotropic hormone (PTTH) that activates prothoracic glands, which secrete a second hormone, usually ecdysone (an ecdysteroid ), that induces ecdysis (shedding of the exoskeleton). PTTH also stimulates the corpora allata , a retrocerebral organ, to produce juvenile hormone , which prevents

825-407: The larvae are fed by female workers. In Ropalidia marginata (a paper wasp) the males are also capable of feeding larvae but they are much less efficient, spending more time and getting less food to the larvae. The larvae of some organisms (for example, some newts ) can become pubescent and do not develop further into the adult form. This is a type of neoteny . It is a misunderstanding that

858-407: The larvae are fed by female workers. In Ropalidia marginata (a paper wasp) the males are also capable of feeding larvae but they are much less efficient, spending more time and getting less food to the larvae. The larvae of some organisms (for example, some newts ) can become pubescent and do not develop further into the adult form. This is a type of neoteny . It is a misunderstanding that

891-525: The larval form always reflects the group's evolutionary history . This could be the case, but often the larval stage has evolved secondarily, as in insects. In these cases , the larval form may differ more than the adult form from the group's common origins. Within Insects , only Endopterygotes show complete metamorphosis, including a distinct larval stage. Several classifications have been suggested by many entomologists , and following classification

924-471: The larval form always reflects the group's evolutionary history . This could be the case, but often the larval stage has evolved secondarily, as in insects. In these cases , the larval form may differ more than the adult form from the group's common origins. Within Insects , only Endopterygotes show complete metamorphosis, including a distinct larval stage. Several classifications have been suggested by many entomologists , and following classification

957-566: The most significant being the inclusion, in holometabolous organisms, of a pupal or resting stage between the larval and adult forms. In hemimetabolous insects , immature stages are called nymphs . Development proceeds in repeated stages of growth and ecdysis (moulting); these stages are called instars . The juvenile forms closely resemble adults, but are smaller and lack adult features such as wings and genitalia. The size and morphological differences between nymphs in different instars are small, often just differences in body proportions and

990-486: The number of segments; in later instars, external wing buds form. The period from one molt to the next is called a stadium. In holometabolous insects, immature stages are called larvae and differ markedly from adults. Insects which undergo holometabolism pass through a larval stage, then enter an inactive state called pupa (called a "chrysalis " in butterfly species), and finally emerge as adults. The earliest insect forms showed direct development ( ametabolism ), and

1023-408: The thyroid hormone. Examples among the non-bony fish include the lamprey . Among the bony fish, mechanisms are varied. The salmon is diadromous , meaning that it changes from a freshwater to a saltwater lifestyle. Many species of flatfish begin their life bilaterally symmetrical , with an eye on either side of the body; but one eye moves to join the other side of the fish – which becomes

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1056-461: The upper side – in the adult form. The European eel has a number of metamorphoses, from the larval stage to the leptocephalus stage, then a quick metamorphosis to glass eel at the edge of the continental shelf (eight days for the Japanese eel ), two months at the border of fresh and salt water where the glass eel undergoes a quick metamorphosis into elver, then a long stage of growth followed by

1089-526: The windows are phylogenetically adapted to the ecological circumstances insects are living in. According to research from 2008, adult Manduca sexta is able to retain behavior learned as a caterpillar . Another caterpillar, the ornate moth caterpillar , is able to carry toxins that it acquires from its diet through metamorphosis and into adulthood, where the toxins still serve for protection against predators. Many observations published in 2002, and supported in 2013 indicate that programmed cell death plays

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