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Literally, "hidden life." When an animal or plant becomes so inactive that its life processes almost come to a stop, it is said to enter cryptobiosis. There are a surprising number of organisms which can do this, including plants (as seeds), many kinds of spores, rotifers, nematodes, collembolans, tardigrades, the eggs of some crustaceans, and the larvae of at least one insect, Polypedilum vanderplanki (an African midge).

The phenomenon is best documented among the tardigrades and other minute inhabitants of mosses and lichens, where the water film essential for active life is transient and sporadic. When the film dries out these animals appear to be dead for periods of days, weeks, or even years until moisture returns, when they 'come back to life' and resume their normal activities.

Entering cryptobiosis involves various processes. The animal typically retracts its legs and other appendages, or curls up into a ball to minimize its surface area. Biochemical changes in the cuticle or the secretion of wax ensure that at least some water is retained, although this may be only some 5% of the normal content, and the body and the internal organs contract and shrivel. Sugars manufactured by the body cells protect the integrity of the cell membranes and also convert the cytoplasm to a glasslike state. Absorbing water reverses these processes.

Besides allowing survival during dry periods, the overall lifespan of the organism may be hugely increased by lengthy periods of cryptobiosis; also the dry form may be easily carried by the wind to a new environment, allowing the spread of these mostly tiny organisms which would otherwise have very limited mobility.

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