larva

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larva

, in zoology
larva, independent, immature animal that undergoes a profound change, or metamorphosis, to assume the typical adult form. Larvae occur in almost all of the animal phyla; because most are tiny or microscopic, they are rarely seen. They play diverse roles in the lives of animals. Motile larvae help to disseminate sessile, or sedentary, animals such as sponges, oysters, barnacles, or scale insects. Larvae of parasites may be dispersed by penetrating the skin of new hosts; other parasite larvae live in intermediate hosts that are normally eaten by the final host, in which the adult parasites develop. The larvae of other parasites live in and are dispersed by intermediate hosts such as mosquitoes, gnats, or leeches; when the blood meals are taken from the final host, the parasite larvae are introduced into the blood or skin. Parasitic infections can often be reduced by eliminating the larval hosts.

Vertebrate Larvae

Among vertebrates a number of fishes pass through larval stages; the larva of the eel is interesting because it is flat and transparent. The tadpole, the familiar larva of the amphibian, develops to a considerable size in the relatively hospitable aquatic environment before metamorphosis prepares it for an amphibious or terrestrial life as a frog or toad.

Insect Larvae

In some animals, especially insects, larvae represent a special feeding stage in the life cycle. Some insects pass through more or less wormlike larval stages, enter the outwardly inactive, or pupal, form, and emerge from the pupal case as adults (see pupa). The importance of larvae in the life cycle of insects varies greatly, as does the proportion of the life span spent in larval, pupal, and adult stages. In many insects, the adult life is relatively short, consisting mostly of mating and egg laying, while the larvae live for many months or, in some species, for several years. Insect larvae feed voraciously, necessarily becoming larger than the adult, as considerable energy and material are needed for the profound changes made during pupation. For this reason, insect larvae often cause far more damage to stored crops and textiles than adult insects.

Insect larvae generally have a thinner exoskeleton than the adult; many are white and soft. The characteristic fly larvae are maggots, often developing in decaying plant or animal material. Mosquito larvae are the familiar aquatic wrigglers; they breathe air and are killed by a thin film of oil on the water that prevents contact with air. Maggots and wrigglers are legless, as are all larvae of the insect order Diptera. Beetle larvae, including the whitish forms called grubs and the long brownish wireworms, are quite diverse, but all are equipped with the six legs characteristic of adults. Moths and butterflies have wormlike caterpillars as larvae, each equipped with the six legs characteristic of adults and false legs known as prolegs to support the long abdominal section. Some, like the milkweed worm (the larva of the monarch butterfly), are relatively naked, while other caterpillars are covered by hairy bristles, sometimes equipped with irritating chemicals that can cause intense itching. The young of the social insects (bees, ants, wasps, and termites) are legless but otherwise grublike. Although all social-insect larvae are ultimately dependent on the parent colony for food, they are considered true larvae because they pass through a pupal stage.

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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Larva

 

a stage in the individual development of many invertebrates and some vertebrates (fishes and amphibians) in which the nutrient reserves of the egg are insufficient to complete embryonic development.

An organism in the larval stage is self-sufficient. Usually it has special organs not characteristic of the adult form but lacks other organs characteristic of the adult. In many animals, the existence of the larval stage is determined by the differences in the modes of life of the early stages of development and that of the adult stage; thus, the trochophore, characteristic of polychaetes and many mollusks, is free-swimming, but the adult form is benthic. The presence of a larva is sometimes associated with a change in habitat in the course of development. For example, many amphibian larvae are adapted to aquatic life, whereas the adult animals are adapted to dry land. In sessile or sluggish marine animals, a free-swimming larva ensures offspring distribution. This is true of the larvae of sponges and coelenterates (paren-chymula, amphiblastula, planula) and of echinoderms and enteropneusts (dipleurula).

The metamorphosis of the larva to the adult animal consists in the restructuring of the larva’s organization; the more profound that restructuring, the greater will be the difference between the larva and the adult organism. The changes that occur in the metamorphosis of certain invertebrates (nemertines, echinoderms, and insects) are especially pronounced. For example, in higher insects in the pupal stage (which follows the larval stage), almost all of the larval organs are destroyed. The organs of the adult animal are formed de novo from special rudiments called imaginal disks. The larvae of some animals retain the structural characteristics of ancestral forms. For example, phylogenetic significance of this sort is ascribed to the larvae of sponges and coelenterates (parenchymula, planula) and to the caudate larvae of ascidians, which resemble a free-swimming ancestor in structure.

A. V. IVANOV

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

larva

[′lär·va]
(invertebrate zoology)
An independent, immature, often vermiform stage that develops from the fertilized egg and must usually undergo a series of form and size changes before assuming characteristic features of the parent.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

larva

an immature free-living form of many animals that develops into a different adult form by metamorphosis
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
Ocular larva migrans is typically unilateral and occurs when larvae migrate to the eye.
Visceral and ocular larva migrans. Semin Vet Med Surg (Small Anim) 1991;6:227-235.
Roundworms produce two disease syndromes in people - Visceral larva migrans (VLM) and Ocular larva migrans (OLM).
Risk factors for toxocaral ocular larva migrans: a case-control study.
migrans, ocular larva migrans, urticaria, pulmonary nodules, hepatic and