Cryptobiosis or anabiosis is a metabolic state of life entered by an organism in response to adverse environmental conditions such as desiccation, freezing, and oxygen deficiency. In the cryptobiotic state, all measurable metabolic processes stop, preventing reproduction, development, and repair. When environmental conditions return to being hospitable, the organism will return to its metabolic state of life as it was prior to the cryptobiosis. Forms Anhydrobiosis Anhydrobiosis is the most studied form of cryptobiosis and occurs in situations of extreme desiccation. The term anhydrobiosis derives from the Greek for "life without water" and is most commonly used for the desiccation tolerance observed in certain invertebrate animals such as bdelloid rotifers, tardigrades, brine shrimp, nematodes, and at least one insect, a species of chironomid (Polypedilum vanderplanki). However, other life forms exhibit desiccation tolerance. These include the resurrection plant Craterostigma plantagineum, the majority of plant seeds, and many microorganisms such as bakers' yeast. Studies have shown that some anhydrobiotic organisms can survive for decades, even centuries, in the dry state. Invertebrates undergoing anhydrobiosis often contract into a smaller shape and some proceed to form a sugar called trehalose. Desiccation tolerance in plants is associated with the production of another sugar, sucrose. These sugars are thought to protect the organism from desiccation damage. In some creatures, such as bdelloid rotifers, no trehalose has been found, which has led scientists to propose other mechanisms of anhydrobiosis, possibly involving intrinsically disordered proteins. In 2011, Caenorhabditis elegans, a nematode that is also one of the best-studied model organisms, was shown to undergo anhydrobiosis in the dauer larva stage. Further research taking advantage of genetic and biochemical tools available for this organism revealed that in addition to trehalose biosynthesis, a set of other functional pathways is involved in anhydrobiosis at the molecular level. These are mainly defense mechanisms against reactive oxygen species and xenobiotics, expression of heat shock proteins and intrinsically disordered proteins as well as biosynthesis of polyunsaturated fatty acids and polyamines. Some of them are conserved among anhydrobiotic plants and animals, suggesting that anhydrobiotic ability may depend on a set of common mechanisms. Understanding these mechanisms in detail might enable modification of non-anhydrobiotic cells, tissues, organs or even organisms so that they can be preserved in a dried state of suspended animation over long time periods. As of 2004, such an application of anhydrobiosis is being applied to vaccines. In vaccines, the process can produce