After the asexual reproduction stage cercaria ( another free-swimming larva ) are generated in large quantities, which then leave ( shed into the environment ) the snail and must infect a suitable vertebrate host.

On penetration, the head of the cercaria transforms into an endoparasitic larva, the schistosomule.

This system of asexual reproduction allows for an exponential multiplication of cercaria individuals from one miracidium.

The cercaria emerge from the snail during daylight and they propel themselves in water with the aid of their bifurcated tail, actively seeking out their final host.

This occurs in three stages, an initial attachment to the skin, followed by the cercaria creeping over the skin searching for a suitable penetration site, often a hair follicle, and finally penetration of the skin into the epidermis using proteolytic secretions from the cercarial post-acetabular, then pre-acetabular glands.

Aquatic snails, which represent the first intermediate hosts of Opisthorchis viverrini, ingest the eggs from which the miracidia undergo asexual reproduction before a population of the free swimming larval stage, called a cercaria, is shed from the infected snails.

A cercaria has a tapering head with large penetration glands.

These embryos move to the brood sac and mature into cercaria.

The redia themselves house the asexual reproduction of free-swimming cercaria.

Once inside of the fish muscle, the cercaria create a protective metacercarial cyst with which to encapsulate their bodies.

They become infected when the larvae ( cercaria ) of the worm penetrates the flesh of the fish.

Rather than further developing into a cercaria which leaves the snail to infect the second intermediate host as usual for trematodes, they directly develop into encysted metacercariae in the snail.

The life cycle of Fasciola gigantica is as follows: eggs ( transported with feces ) → eggs hatchs → miracidium → miracidium infect snail intermediate host → ( parthenogenesis in 24 hours ) sporocyst → redia → daughter redia → cercaria → ( gets outside the snail ) → metacercaria → infection of the host → adult stage produces eggs.

The miracidia go through several stages in the mollusc host, eventually emerging as motile cercaria larvae.

The cercaria infect vertebrates either through the skin or are ingested.

In its vertebrate host, the cercaria matures to an adult form, and lays eggs that are discharged with the host faeces or urine.

The motile cercaria finds and settles in a host where it will become either an adult, or a mesocercaria, or a metacercaria, according to species.

** Mesocercaria – a cercaria little modified but resting.

** Metacercaria – a cercaria encysted and resting.

In some species, the cercaria develops into an adult within the same host.

In some species ( for example Ribeiroia ) the cercaria encysts, and waits until the host is eaten by a third host, in whose gut it emerges and develops into an adult.

Once the cercaria penetrates the skin of the host it loses its tail and becomes a schistosomule.

Following this, the parasite develops via a so-called mother-sporocyst and daughter-sporocyst generation to the cercaria.

From a single miracidium result a few thousand cercaria, every one of which is capable of infecting man.

During one of their life stages, the larvae of the parasite, cercaria, leave the water snails and swim freely in the freshwater, attempting to encounter water birds.

This is usually because of adverse conditions such as low water temperatures which may inhibit the production of thyroxine or prevent the larva from reacting to the hormone in the normal way.

Here, the imago develops from imaginal discs found inside the larva.

Anopheles larva from southern Germany, about 8 mm long

Although some species hatch directly into the adult form, many have a trochophore larva, which metamorphoses into the adult after anything from a day to a month, depending on species.

The female then separates from the feeding stage and attaches herself to another host, where the larva in her develops.

In some species, the larva briefly develops a segmented body before transforming into the adult body plan, supporting the theory that echiruans evolved from segmented ancestors resembling more typical annelids.

A third class, Planctosphaeroidea, is known only from the larva of a single species.

The animal mesomeres of P. flava go on to give rise to the larva ’ s ectoderm, animal blastomeres also appear to give rise to these structures though the exact contribution varies from embryo to embryo.

This is lined with a thin coating of wax which prevents the egg from drying out before the larva has had time to fully develop.

Near the end of each instar, the larva undergoes a process called apolysis, in which the cuticle, a tough outer layer made of a mixture of chitin and specialized proteins, is released from the softer epidermis beneath, and the epidermis begins to form a new cuticle beneath.

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

Nauplius ( larva ) | Nauplius of an unidentified prawn from the family Penaeidae

Woodpeckers and sapsuckers can feed on the larva from their cases.

Newborn larva emerge from the bottom of the hanging case and drop down on a strand of silk.

The wind often blows the larva to nearby plants where it begins its new case from silk and fecal material before beginning to add leaves and twigs from its host.

When mature in mid-August, the larva wraps silk around a branch, hangs from it, and pupates head down.

They are created at the decision of the worker bees by feeding a larva only royal jelly throughout its development, rather than switching from royal jelly to pollen once the larva grows past a certain size.

Roughly speaking, there is some anatomical distinction between the larvae of the Nematocera and the Brachycera ( see Classification section, below ); especially in the Brachycera, there is little demarcation between the thorax and abdomen, though the demarcation may be very visible in many Nematocera, such as mosquitoes ( see image, both here and in the mosquitoes article ); in the Brachycera, the head of the larva is not clearly distinguishable from the rest of the body, and there are few, if any, sclerites.

Five developmental stages follow: the prelarva hatches from the egg and has only weakly developed mouthparts and nine abdominal segments ; larva I follows and has fully developed mouthparts ; larva II has ten abdominal segments ; maturus junior has twelve abdominal segments and is followed by the adult.

Perhaps its origins are related to the Old English " maða " meaning " maggot " or from the root of " midge " which until the 16th century was used mostly to indicate the larva, usually in reference to devouring clothes.

Yuccas have a very specialized, mutualistic pollination system, being pollinated by yucca moths ( family Prodoxidae ); the insect purposefully transfers the pollen from the stamens of one plant to the stigma of another, and at the same time lays an egg in the flower ; the moth larva then feeds on some of the developing seeds, always leaving enough seed to perpetuate the species.

Under natural circumstances the survival from free swimming larva to 75 mm pike is around 5 percent.