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19 this is "ecdysis" which is the periodic replacement of the external skeleton in arthropods and related groups. The term "molting" for ecdysis is commonly used. ["Molting" occurs throughout the animal kingdom and includes the shedding and replacement of horns, hair, skin, and feathers.] The frequency of molting depends on the rate of growth and, since juveniles grow more quickly than adults, they molt more often. During their first year of growth, between May and September, a crayfish may molt seven to 13 times and triple in size. 9, 234 Most of our crayfishes probably live 2 to 3 years. But there has been no way to age a crayfish or know how long they live because they retain no hard structures for their full life span. The only real way to know a crayfish's age is to keep it in captivity for its full life. However, captive animals seldom have the same life span as one in the wild. It is probable that crayfishes in more northern latitudes grow more slowly and mature later but also live longer. 164 One study used growth rates and size classes to estimate that Devil crayfish in Indiana could live 14 years. 232 But growth is so variable that this technique may not be accurate. So, in a nutshell, the larger a crayfish is, the older it is but perhaps with the continued development of micro-tagging technology we can answer some of these questions. The molt cycle in crayfish has four major phases which are the premolt, the molt, the postmolt, and the intermolt. Premolt: the exoskeleton softens as calcium is extracted from it and stored in a pair of gastroliths ("stomach-stone") which are located in the foregut (see photo at right). At the same time that the old exoskeleton is softening, a new one is forming beneath it. Molt: the old exoskeleton splits at the juncture of the thorax and abdomen and the crayfish kicks itself free. It then goes into hiding as it is extremely vulnerable to predation at this time. Postmolt: the crayfish has a totally soft exoskeleton which must be hardened with new calcium. Part of this calcium comes by re-absorbing the gastroliths. There isn't enough calcium in the gastrolith to completely recalcify the exoskeleton so much of it probably goes directly to the mouthparts so they can eat. 148 The rest of what they need comes from their food (including the old exoskeleton). Intermolt: the period when the exoskeleton is fully re-calcified and the crayfish is free to resume its life. During the premolt, molt, and postmolt periods, the crayfish is soft and vulnerable to cannibalization and predation. As a result, their molt cycle is a dominate factor in their life cycle. Crayfishes occasionally lose limbs, especially chelipeds, but they also have the ability to regenerate these lost limbs. Termed autonomy, their limbs have a membrane across pre-formed breakage points. No muscle tissue passes through this membrane, only blood vessels and nerves. Thus they are able to regrow a lost limb though the regenerated limb does not exactly match the original. The two photos on the next page illustrate normal and regenerated chelipeds. Pair of gastroliths