Ecdysis
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2008-06-21T09:48:56Z
Lambiam
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[[Image:Callinectes sapidus.jpg|thumb|right|240px|Series of pictures showing the progression of ecdysis in ''[[Blue crab|Callinectes sapidus]]'', the blue crab]]
'''Ecdysis''' is the [[molt]]ing of the [[cuticula]] in [[arthropod]]s and related groups ([[Ecdysozoa]]). Since the cuticula of these animals is also the skeletal support (the [[exoskeleton]]) of the body and is inelastic, it is shed during growth and a new, larger covering is formed. The old, empty exoskeleton is called an [[exuvia]] (or "exuvium").
After molting, an arthropod is described as '''teneral'''; it is "fresh", pale and soft-bodied. Within one or two hours, the [[cuticle]] hardens and darkens following a tanning process similar to that of the [[tanning]] of leather. It is during this short phase that the animal grows, since growth is otherwise constrained by the rigidity of the exoskeleton.
Ecdysis may also enable damaged tissue and missing limbs to be [[regeneration (biology)|regenerated]] or substantially re-formed, although this may only be complete over a series of molts, the stump being a little larger with each molt until it is of normal, or near normal size again.
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== Process ==
[[Image:The-arthropods-moulting-1.gif|right|280px]]
In preparation for ecdysis, the arthropod becomes inactive for a period of time, undergoing [[apolysis]] (separation of the old exoskeleton from the underlying epidermal cells). For most organisms, the resting period is a stage of preparation during which the secretion of fluid from the molting glands of the epidermal layer and the loosening of the underpart of the cuticle occur.
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[[Image:The-arthropods-moulting-2.gif|right|280px]]
Once the old cuticle has separated from the epidermis, the digesting fluid is secreted into the space in between them. However, this fluid remains inactive until the upper part of the new cuticle has been formed.
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[[Image:The-arthropods-moulting-3.gif|right|280px]]
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 [[invertebrate trachea|trachea]]e if they are present.
Then, by crawling movements, the [[pharate]] animal pushes forward in the old [[Integumentary system|integumentary shell]], which splits down the back allowing the animal to emerge. Often, this initial crack is caused by an increase in blood pressure within the body (in combination with movement), forcing an expansion across its [[exoskeleton]], leading to an eventual crack that allows for certain organisms such as [[spider]]s to extricate themselves.
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==Molting in insects==
[[Image:Cicada_molting_animated-2.gif|right|thumb|A [[cicada]] molting]]
Each stage in the development of an insect between molts is called an [[instar]], or stadium. [[Endopterygota]] tend to have few instars (4-5), while other insects such as [[Exopterygota]] can have anywhere up to 15. Endopterygota insects have more alternatives to molting, such as expansion of the cuticle and collapse of air sacs to allow growth of internal organs.
The process of molting in insects begins with the separation of the cuticle from the underlying epidermal cells ([[apolysis]]) and ends with the shedding of the old cuticle (ecdysis). In many of them it is initiated by an increase in the [[hormone]] [[ecdysone]]. This hormone causes:
*[[apolysis]] - the separation of the cuticle from the [[Squamous epithelium|epidermis]]
*[[excretion]] of new cuticle beneath the old
*degradation of the old cuticle
After [[apolysis]], molting fluid is secreted into the space between the old cuticle and the epidermis (the [[exuvial]] space), this contains inactive enzymes which are activated only after the new [[epicuticle]] is secreted. This prevents them from digesting the new [[procuticle]] as it is laid down. The lower regions of the old cuticle - the [[endocuticle]] and [[mesocuticle]] - are then digested by the enzymes and subsequently absorbed. The [[exocuticle]] and [[epicuticle]] resist digestion and are hence shed at ecdysis.
==Gallery==
<gallery>
Image:Actias luna 4th instar ecdysis sjh.JPG|[[Actias luna|Luna moth]] [[caterpillar]] just after ecdysis. The old exoskeleton is visible behind it.
Image:2004-11-07 Blatta orientalis ecdysis.jpg|Oriental cockroach molting.
</gallery>
==External links==
*{{Cite journal |quotes=no |journal= PLoS Biology |volume=3 |issue=10 |pages=e349 |url=http://biology.plosjournals.org/perlserv/?request=get-document&doi=10.1371/journal.pbio.0030349 |title=How the Ecdysozoan Changed Its Coat |date=[[2005-10-11]] |author=John Ewer | doi = 10.1371/journal.pbio.0030349 <!--Retrieved from Yahoo! by DOI bot-->}}
*[http://johnbokma.com/mexit/2006/03/23/centruroides-scorpions-molting.html Scorpion (''Centruroides gracilis'') molting] - several pictures.
[[Category:Developmental biology]]
[[Category:Arthropod anatomy]]
[[ca:Ècdisi]]
[[de:Häutung]]
[[el:Έκδυση]]
[[es:Muda (biología)]]
[[fr:Mue des arthropodes]]
[[la:Ecdysis]]
[[nl:Vervelling]]
[[ja:脱皮]]
[[no:Hudskifte]]
[[pt:Ecdise]]