barely recognisable as a crab, radically changes its form when it undergoes ecdysis as it matures over the eyes, strong biomineralization over the
pincers, and tough chitin fabric in the joints and the bristles on the legs
repletes, the abdomens of the workers that hold the sugar solution grow vastly, but only the unsclerotised cuticle can stretch, leaving the unstretched sclerites as dark islands on the clear abdomen larva is hardly recognisable as a crab, but each time it sheds its cuticle it remodels itself, eventually taking on its final crab form The chemical and physical nature of the arthropod exoskeleton limits its ability to stretch or change shape as the animal grows. In some special cases, such as the abdomens of termite queens and honeypot ants, distention of the abdomen can occur through the process of
neosomy, which, in the case of
Tunga fleas, occurs through expansion of the
arthrodial membranes. In general, however, the rigidity of the exoskeleton means that continuous growth of arthropods is not possible. Therefore, growth is periodic and concentrated into a period of time when the exoskeleton is shed, called
moulting or
ecdysis, which is under the control of a hormone called
ecdysone. Moulting is a complex process that is invariably dangerous for the arthropod involved. Before the old exoskeleton is shed, the cuticle separates from the epidermis through a process called
apolysis. Early in the process of apolysis the epithelial cells release enzymatic moulting fluid between the old cuticle and the epidermis. The enzymes partly digest the endocuticle and the epidermis absorbs the digested material for the animal to assimilate. Much of that digested material is re-used to build the new cuticle. Once the new cuticle has formed sufficiently, the animal splits the remaining parts of the old integument along built-in lines of weakness and sheds them in the visible process of ecdysis, generally shedding and discarding the epicuticle and the reduced exocuticle, though some species carry them along for camouflage or protection. The shed portions are called the
exuviae. After the old cuticle is shed, the arthropod typically pumps up its body (for example, by air or water intake) to allow the new cuticle to expand to a larger size: the process of hardening by dehydration of the cuticle then takes place. The new integument still is soft and usually is pale, and it is said to be
teneral or
callow. It then undergoes a hardening and pigmentation process that might take anything from several minutes to several days, depending on the nature of the animal and the circumstances. Although the process of ecdysis is metabolically risky and expensive, it does have some advantages. For one thing it permits a complex development cycle of
metamorphosis in which young animals may be totally different from older phases, such as the
nauplius larvae of crustaceans, the nymphs of say, the
Odonata, or the larvae of
Endopterygota, such as maggots of flies. Such larval stages commonly have
ecological and life cycle roles totally different from those of the mature animals. Secondly, often a major injury in one phase, such as the loss of a leg from an insect nymph, or a claw from a young crab, can be repaired after one or two stages of ecdysis. Similarly, delicate parts that need periodic replacement, such as the outer surfaces of the eye lenses of spiders, or the
urticating hairs of caterpillars, can be shed, making way for new structures. File:Bienenwabe mit Eiern und Brut 5 larva.png| Honeybee larvae have flexible but delicate unsclerotised cuticles. File:Birgus latro 2.jpg| This fully-grown
robber crab has tough fabric forming its joints, delicate
biomineralized cuticle over its sensory
antennae, optic-quality over its eyes, and strong, calcite-reinforced chitin armouring its body and legs; its
pincers can break into coconuts File:Kaldari Phidippus johnsoni male defense cropped.jpg|The Fangs in Spiders' chelicerae are so sclerotised as to be greatly hardened and darkened == See also ==