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Moulting And Ecdysis

Submitted by Mousumi Sepai, Last Modified on 2021-03-12

In biology, moulting /molting or in other terms as sloughing, shedding, which is known as ecdysis in many invertebrates, is a process in which a living organism routinely casts off a part of its own body. It happens specific times of the year or at specific points in its life which is mostly involved with outer skin or cover.

Moulting is mainly involved with shedding the epidermis(outer skin) or pelage like hair,feathers, fur, wool etc. or other external layers. And in some other organism’s some body parts for example, wings in some insects or the entire exoskeleton in arthropods.

Ecdysis is the shedding process of the cuticle in many invertebrates of the clade ecdysozoa, which typically forms a largely inelastic exoskeleton. During the phase of growth the old cuticle is replaced by a new, larger exoskeleton. The remnants of the old, empty exoskeleton are called exuviae.

In arthropods(insects, arachnids and crustaceans) ecdysis is the shedding of the exoskeleton (shell), typically to let the organism grow. Because of the rigidness the exoskeleton cannot expand like skin, but this is simplistic, ignoring the fact that most Arthropoda with soft, flexible skins also undergo ecdysis. Ecdysis mainly helps with metamorphosis, the radical difference between the morphology of successiveinstars, and the fact that a new skin can replace structures, such as by providing new external lenses for eyes. The new exoskeleton slowly hardens after the moulting of the old exoskeleton. The old exoskeleton is called an exuviae. While moulting, insects can't breathe.

After moulting, an arthropod is described as teneral, a callow. At that moment the insects are pale and soft-bodied. It takes a few hours to harden the cuticle and the colour slowly becomes darker,a tanning process analogous to the production of leather. This is an important phase, when the animal grows, since growth is otherwise constrained by the rigidity of the exoskeleton. Growth of the body parts normally covered by hard exoskeleton is achieved by supply of body fluids from soft parts before the new skin hardens. Some arthropods, especially large insects with tracheal respiration, expand their new exoskeleton by swallowing or otherwise taking in air. The maturation of the structure and colouration of the new exoskeleton might take a longer time in a long-lived insect; which causes difficulty to identify an individual which recently underwent ecdysis.

Also sometimes ecdysis helps to replace any damaged tissue and missing limbs to be regenerated or substantially re-formed. This process could be completed over a series of regeneration which contains a series of moults, the stump becoming a little larger with each moult until it is a normal, or near normal, size again.

In the phase of ecdysis, the arthropod becomes inactive for a period of time, undergoing apolysis or separation of the old exoskeleton from the underlying epidermal cells. The inactive period is a stage of preparation, which is the secretion of fluid from the moulting glands of the epidermal layer and the loosening of the underpart of the cuticle occur. A digestive fluid fills the space between the epidermis and the old cuticle, After the old cuticle has separated from the epidermis. This digestive fluid only activates after the upper part of the new cuticle has been formed. The organism pushes forward in the old integumentary shell in a crawling movement, which splits down the back allowing the animal to emerge. Often, this initial crack is caused by a combination of . The movement and the increasing blood pressure, forcing an expansion across its exoskeleton, produce the initial crack, which allows for certain organisms such as spiders to extricate themselves. While the old cuticle is being digested, the new layer is secreted. All cuticular structures are shed at ecdysis, including the inner parts of the exoskeleton, which includes terminal linings of the alimentary tract and of the tracheae if they are present.

Ecdysone is a steroid prohormone of the major moulting hormone 20-hydroxyecdysone, which is secreted from the prothoracic glands. Insect moulting hormones are generally called ecdysteroids. Ecdysteroids usually act as moulting and as usual as sex hormones in arthropods but in some other cases in phyla they play different roles. Which include ecdysone and it’s homologous such as 20-hydroxyecdysone. Phytoecdysteroids can sometimes be found in many plants mostly as a protection agent against herbivore insects. In Drosophila melanogaster, an increase in ecdysone concentration induces the expression of genes coding for proteins that the larvae require and it causes chromosome puffs to form in many plants mostly as a protection agent against herbivorous insects. These phytoecdysteroids have been reputed to have medicinal value and are part of herbal adaptogenic remedies like cordyceps. Yet an ecdysteroids precursor in plants has been shown to have cytotoxic properties. A pesticide sold the name MIMIC has ecdysteroid activity although it’s chemical structure has little resemblance to the ecdysteroids.

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