Larva

Selected types of larvae. List of larvae. Chrysalis, caterpillar, crustacean larvae. The life cycles of insects. The larva's appearance. Animals in the larval stage. Paralarvae are young cephalopods in the planktonic stages between hatchling and subadult.

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Introduction

The word insect dates back to 1600, from the Latin word insectum, meaning "with a notched or divided body", or literally "cut into", from neuter plural of insectare, "to cut into, to cut up," from in- "into" + secare "to cut"; because insects are "cut into" three sections. The word created by Pliny the Elder's loan-translation of the Greek word ??????? (entomon) or "insect" (as in entomology), which was Aristotle's term for this class of life, also in reference to their "notched" bodies, first documented in English in 1601 in Holland's translation of Pliny. Translations of Aristotle's term also form the usual word for "insect" in Welsh (trychfil, from trychu "cut" and mil, "animal"), Serbo-Croatian (zareznik, from rezati, "cut"), Russian (насекомое nasekomoe, from sekat, "cut"), etc.

Insects (from Latin insectum, a calque of Greek ??????? [entomon], "cut into sections") are a class of invertebrates within the arthropod phylum that have a chitinous exoskeleton, a three-part body (head, thorax and abdomen), three pairs of jointed legs, compound eyes and one pair of antennae. They are among the most diverse groups of animals on the planet, including more than a million described species and representing more than half of all known living organisms. The number of extant species is estimated at between six and ten million, and potentially represent over 90% of the differing metazoan life forms on Earth. Insects may be found in nearly all environments, although only a small number of species occur in the oceans, a habitat dominated by another arthropod group, crustaceans.

The life cycles of insects vary (from one day to a few years), but most hatch from eggs. Insect growth is constrained by the inelastic exoskeleton and development involves a series of molts. The immature stages can differ from the adults in structure, habit and habitat, and can include a passive pupal stage in those groups that undergo complete metamorphosis. Insects that undergo incomplete metamorphosis lack a pupal stage and adults develop through a series of nymphal stages. The higher level relationship of the hexapoda is unclear. Fossilized insects of enormous size have been found from the Paleozoic Era, including giant dragonflies with wingspans of 55 to 70 cm (22-28 in). The most diverse insect groups appear to have coevolved with flowering plants.

Adult insects typically move about by walking, flying or sometimes swimming. As it allows for rapid yet stable movement, many insects adopt a tripedal gait in which they walk with their legs touching the ground in alternating triangles. Insects are the only invertebrates to have evolved flight. Many insects spend at least part of their lives underwater, with larval adaptations that include gills, and some adult insects are aquatic and have adaptations for swimming. Some species, such as water striders, are capable of walking on the surface of water. Insects are mostly solitary, but some, such as certain bees, ants and termites, are social and live in large, well-organized colonies. Some insects, such as earwigs, show maternal care, guarding their eggs and young. Insects can communicate with each other in a variety of ways. Male moths can sense the pheromones of female moths over great distances. Other species communicate with sounds: crickets stridulate, or rub their wings together, to attract a mate and repel other males. Lampyridae in the beetle order Coleoptera communicate with light.

Humans regard certain insects as pests, and attempt to control them using insecticides and a host of other techniques. Some insects damage crops by feeding on sap, leaves or fruits. A few parasitic species are capable of transmitting diseases to humans, pets and livestock. Some insects perform complex ecological roles; blow-flies, for example, help consume carrion and dead or diseased tissue but also spread diseases. Insect pollinators are essential to the life-cycle of many flowering plant species on which most organisms, including humans, are at least partly dependent; without them, the terrestrial portion of the biosphere (including humans) would be devastated. Many other insects are considered ecologically beneficial as predators and a few provide direct economic benefit. Silkworms and bees have been used extensively by humans for the production of silk and honey, respectively. In some cultures, the larvae or adults of certain insects are a food-source for humans.

1. Larva

Larva of Papilio xuthus, butterfly/

A larva (plural larvae rv) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle.

The larva's appearance is generally very different from the adult form (e.g. caterpillars and butterflies). A larva often has unique structures and organs that do not occur in the adult form, and may have a considerably different diet.

Larvae are frequently adapted to environments separate from adults. For example, some larvae such as tadpoles live exclusively in aquatic environments, but can live outside water as adult frogs. By living in 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. Some species such as barnacles are immobile as adults, and use their mobile larval form to distribute themselves.

The larvae of some species (for example, some newts) can become pubescent and not further develop into the adult form. This is a type of neoteny.

It is a misunderstanding that 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 origin.

2. Selected types of larvae

Animal

Name of larva

Hydrozoa

planula

Many crustaceans

nauplius

Decapoda

zoea

Mayflies, Grasshoppers, True Bugs, etc.

nymph

Dragonflies, Damselflies

naiad, nymph

Butterflies and moths

caterpillar

Beetles, Bees, Wasps

grub

Flies

maggot

Mosquitos

wriggler

Certain molluscs, annelids

trochophore

Certain molluscs

veliger

Freshwater mussels

glochidium

Lamprey

ammocoete

Fish (generally)

larva

Eels

leptocephalus

Amphibians

tadpole, polliwog

Sea stars

Bipinnaria

3. List of larvae, have separate titles

Axolotl - neotenic larva salamanders (tailed amphibians).

Aktinotroha - larva phoronid.

Auricularia - early phase of larval sea cucumbers.

Bipinnaria - early phase of larvae of sea stars.

Brachiolaria - late phase of larvae of sea stars.

Veliger - larva gastropods and bivalves.

Glaukotoe - larva crawling crustaceans.

Glochidia - larvae of bivalve molluscs.

Tadpole - larva anurans.

Caterpillar - larva of butterflies.

Dipleurula (dipleurula) - common to echinoderms Enteropneusta early form of larvae, later converted to the different groups in the auricularia, bipinnariae, plyuteusa or Tornare.

Doliolaria - middle phase of the larvae of sea cucumbers.

Zoea - Early larvae of decapod crustaceans.

Koretra - wiggler from family Chaoboridae.

Rat - larva of some hover flies (Diptera: Syrphidae).

Leptotsefal - larvae (fry), eels and other fish ugreobraznyh.

Likofora - larva tsestodoobraznyh.

Larva - larvae of sawflies (Hymenoptera-Symphyta).

Lozhnoprovolochnik - darkling beetle larvae families and pyltseedov.

Megalopa - Late larvae of decapod crustaceans.

Metanauplius - larval stage of many species of crustaceans, following the nauplius.

Metatrohofora - larva polychaete annelids, develops from the trochophore and becomes nektohetu.

Mizis - late larva of long-tailed decapod crustaceans (Decapoda-Macrura).

Miracidia - larva sporocysts flukes (Trematoda).

Motyl - Zvontsov larva of mosquito (Diptera: Chironomidae).

Mller larva - larva Turbellaria-poliklad (with many branches) (Polyclada).

Nauplius - early phase of the larvae, characteristic of many crustaceans.

Naiad - dragonfly larvae.

Nektoheta - late larva polychaete annelids, develops from metatrohofory.

Nymph - the traditional name of the larval stage of some arthropods with incomplete metamorphosis (mites and several groups of insects).

Onkomiratsidy - larva monogeneans (monogenetic trematodes).

Oncosphere or shestikryuchnaya larva - larva of tapeworms (Cestoda).

Grubs - larvae krugloshovnyh flies.

Parenhimula - larva sponges.

Pentakula - late phase of development of the larvae of sea cucumbers.

Peskoroyka - lamprey larvae.

Pilidi - larva nemerteans.

Planktosfera - larva Enteropneusta.

Planula - larva of coelenterates.

Plyuteus or pluteus - larvae of echinoderms. The larvae of brittle stars and sea urchins use special terms:

Ofioplyuteus or ofiopluteus - larva of brittle stars;

Ehinoplyuteus or ehinopluteus - larva of sea urchins.

Wireworms - larvae of click beetles.

Protozoea - larva of crustaceans, which emerged from the egg.

Protonymphon - larva of sea spiders.

Plate of worm - midge larva selfless.

Tornare - Enteropneusta larva.

Triungulin - the initial phase of development of the larvae of insects with gipermetamorfozom.

Trochophore - early larva trohofornyh animals (clams, polychaete annelids, sipunkulid etc.).

Finn

Cercaria - trematode larvae of flukes (Trematoda).

Tsiprisovidnaya larva - the last larval stage of barnacles.

Cysticerci - a type of larval development - Bowie some tapeworms. Similar to cysticercoids.

Cysticercoids - a type of larval development - Bowie some tapeworms.

Tsifonaut (tsifonautes) - larva of bryozoans.

Shestikryuchnaya larva, or oncosphere - larva of tapeworms (Cestoda).

larvae chrysalis caterpillar crustacean

4. Chrysalis

Common Crow butterfly (Euploea core) chrysalis illustrating the Greek origin of the term : ?????? (chrysos) for gold

A chrysalis (Latin chrysallis, from Greek ????????? = chrysallis, pl: chrysalides, also known as an aurelia) or nympha is the pupal stage of butterflies. The term is derived from the metallic gold-coloration found in the pupae of many butterflies, referred to by the Greek term ?????? (chrysos) for gold.

When the caterpillar is fully grown, it makes a button of silk which it uses to fasten its body to a leaf or a twig. Then the caterpillar's skin comes off for the final time. Under this old skin is a hard skin called a chrysalis.

Because chrysalides are often showy and are formed in the open, they are the most familiar examples of pupae. Most chrysalides are attached to a surface by a Velcro-like arrangement of a silken pad spun by the caterpillar, usually cemented to the underside of a perch, and the cremaster, a hook-shaped protuberance from the rear of the chrysalis at the tip of the pupal abdomen by which the caterpillar fixes itself to the pad of silk.

Like other types of pupae, the chrysalis stage in most butterflies is one in which there is little movement. However, some butterfly pupae are capable of moving the abdominal segments to produce sounds or to scare away potential predators. Within the chrysalis, growth and differentiation occur. The adult butterfly emerges (ecloses) from this and expands its wings by pumping haemolymph into the wing veins. Although this sudden and rapid change from pupa to imago is often called metamorphosis, metamorphosis is really the whole series of changes that an insect undergoes from egg to adult.

On emerging the butterfly uses a liquid which softens the shell of the chrysalis. Additionally, it uses two sharp claws located on the thick joints at the base of the forewings to help make its way out. Having emerged from the chrysalis, the butterfly will usually sit on the empty shell in order to expand and harden its wings. However, if the chrysalis was near the ground (such as if it fell off from its silk pad), the butterfly would find another vertical surface to rest upon and harden its wings (such as a wall or fence).

Moth pupae are usually dark in color and either formed in underground cells, loose in the soil, or their pupa is contained in a protective silk case called a cocoon.

It is important to differentiate between pupa, chrysalis and cocoon. The pupa is the stage between the larva and adult stages. The chrysalis is a butterfly pupa. A cocoon is a silk case that moths, and sometimes other insects, spin around the pupa.

5. Caterpillar

Caterpillars are the larval form of members of the order Lepidoptera (the insect order comprising butterflies and moths). They are mostly herbivorous in food habit, although some species are insectivorous. Caterpillars are voracious feeders and many of them are considered to be pests in agriculture. Many moth species are better known in their caterpillar stages because of the damage they cause to fruits and other agricultural produce.

The etymological origins of the word are from the early 16th century, from Middle English catirpel, catirpeller, probably an alteration of Old North French catepelose: cate, cat (from Latin cattus) + pelose, hairy (from Latin pilosus).

The geometrids, also known as inchworms or loopers, are so named because of the way they move, appearing to measure the earth (the word geometrid means earth-measurer in Greek); the primary reason for this unusual locomotion is the elimination of nearly all the prolegs except the clasper on the terminal segment.

Caterpillars have soft bodies that can grow rapidly between moults. Only the head capsule is hardened. The mandibles are tough and sharp for chewing leaves (this contrasts with most adult Lepidoptera, which have highly reduced or soft mandibles). Behind the mandibles of the caterpillar are the spinnerets, for manipulating silk.

Some larvae of the Hymenoptera order (ants, bees and wasps) can appear like the caterpillars of the lepidoptera. Such larvae are mainly seen in the sawfly family. However while these larvae superficially resemble caterpillars, they can be distinguished by the presence of prolegs on every abdominal segment, an absence of crochets or hooks on the prolegs (these are present on lepidopteran caterpillars), prominent ocelli on the head capsule, and an absence of the upside-down Y-shaped suture on the front of the head.

6. Crustacean larvae

Crustaceans may pass through a number of larval and immature stages between hatching from their eggs and reaching their adult form. Each of the stages is separated by a moult, in which the hard exoskeleton is shed to allow the animal to grow. The larvae of crustaceans often bear little resemblance to the adult, and there are still cases where it is not known what larvae will grow into what adults. This is especially true of crustaceans which live as benthic adults (on the sea bed), but where the larvae are planktonic and therefore more easily caught.

Many crustacean larvae were not immediately recognised as larvae when they were discovered, and were described as new genera and species. The names of these genera have become generalised to cover specific larval stages across wide groups of crustaceans, such as zoea and nauplius. Other terms described forms which are only found in particular groups, such as the glaucothoe of hermit crabs, or the phyllosoma of slipper lobsters and spiny lobsters.

At its most complete, a crustacean's life cycle begins with an egg, which is usually fertilised, but may instead be produced by parthenogenesis. This egg hatches into a pre-larva or pre-zoea. Through a series of moults, the young animal then passes through various zoea stages, followed by a megalopa or post-larva. This is followed by metamorphosis into an immature form, which broadly resembles the adult, and after further moults, the adult form is finally reached. Some crustaceans continue to moult as adults, while for others, the development of gonads signals the final moult.

Any organs which are absent from the adults do not generally appear in the larvae, although there are a few exceptions, such as the vestige of the fourth pereiopod in the larvae of Lucifer, and some pleopods in certain Anomura and crabs.

7. Paralarva

Paralarvae (singular: paralarva) are young cephalopods in the planktonic stages between hatchling and subadult. This stage differs from the larval stage of animals that undergo true metamorphosis. Paralarvae have been observed only in members of the orders Octopoda and Teuthida.

The term was first introduced by Richard E. Young and Robert F. Harman in 1988.

Chtenopteryx sicula paralarvae. Left: Two very young paralarvae. The circular tentacular clubs bear approximately 20 irregularly arranged suckers. Two chromatophores are present on each side of the mantle. Centre: Ventral, dorsal and side views of a more advanced paralarva. An equatorial circulet of seven large yellow-brown chromatophores is present on the mantle. Posteriorly the expanded vanes of the gladius are visible in the dorsal view. Right: Ventral and dorsal views of a very advanced paralarva.

8. Ichthyoplankton

Ichthyoplankton (from Greek: ikhthus, "fish"; and ????????, planktos, "drifter") are the eggs and larvae of fish. They are usually found in the sunlit zone of the water column, less than 200 metres deep, which is sometimes called the epipelagic or photic zone. Ichthyoplankton are planktonic, meaning they cannot swim effectively under their own power, but must drift with the ocean currents. Fish eggs cannot swim at all, and are unambiguously planktonic. Early stage larvae swim poorly, but later stage larvae swim better and cease to be planktonic as they grow into juveniles. Fish larvae are part of the zooplankton that eat smaller plankton, while fish eggs carry their own food supply. Both eggs and larvae are themselves eaten by larger animals. Ichthyoplankton can be a useful indicator of the state and health of an aquatic ecosystem. For instance, most late stage larvae in ichthyoplankton have usually been predated, so ichthyoplankton tends to be dominated by eggs and early stage larvae. This means that when fish, such as anchovies and sardines, are spawning, ichthyoplankton samples can reflect their spawning output and provide an index of relative population size for the fish. Increases or decreases in the number of adult fish stocks can be detected more rapidly and sensitively by monitoring the ichthyoplankton associated with them, compared to monitoring the adults themselves. It is also usually easier and more cost effective to sample trends in egg and larva populations than to sample trends in adult fish populations.

Interest in plankton originated in Britain and Germany in the nineteenth century when researchers discovered there were microorganisms in the sea, and that they could trap them with fine-mesh nets. They started describing these microorganisms and testing different net configurations. Ichthyoplankton research started in 1864 when the Norwegian government commissioned the marine biologist G. O. Sars to investigate fisheries around the Norwegian coast. Sars found fish eggs, particularly cod eggs, drifting in the water. This established that fish eggs could be pelagic, living in the open water column like other plankton. Around the beginning of the twentieth century, research interest in ichthyoplankton became more general when it emerged that, if ichthyoplankton was sampled quantitatively, then the samples could indicate the relative size or abundance of spawning fish stocks.

Сonclusion

Larva - phase of the life cycle of a number of animals. Usually, the presence of larvae in saying where for individual development undergoes a transformation or metamorphosis - a significant change in the structure.

Typically, the larvae is not developed reproductive system, although in some groups there is neoteny or pedogenesis (gonads begin to function even in the phase of larvae).

The larvae are known in many marine and freshwater invertebrates (eg, worms, mollusks, echinoderms), insects with complete metamorphosis, and a number of vertebrates (for example, some fish and amphibians). Many characteristic larvae have separate names. In some cases (eg, echinoderms), this was due to the fact that they, because of significant differences from the adult form, initially considered separate species of living organisms.

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