Loss of Limbs as a Stimulus to Ecdysis in Brachyura (True Crabs)

Loss of 6 to 8 pereiopods or chelipeds triggers precocious molts in a number of marine crabs including the green crab, Carcinus maenas, the blue crab, Callinectes sapidus, and the fiddler crabs, Uca pugnax and U. pugilator, but not in the spider crab, Libinia emarginata. Mortality rates are negligible compared to those of animals induced to molt by eyestalk removal. 2. Precocious molts call be elicited in the land crab, Gecarcinus lateralis, by the loss of 5 to 8 appendages (pereiopods and chelipeds) but the loss of all 10 appendages inhibits molting. Loss of a cheliped which in Gecarcinus may have a mass ten times greater than a pereiopod is no more effective than loss of a walking leg. 3. The size of the regenerates formed in Gecarcinus is reduced by one-third from normal size when front 1 to 6 pereiopods are lost, and by one-half when 8 limbs are regenerated. 4. When one or more partially regenerated limbs is removed before a certain critical time in the premolt period (Stage D0?) the animal re-regenerates replacement appendage(s). This results in significant lengthening of the interval before ecdysis occurs. Note added in proof: Dr. George D. Bittner (personal communication) finds that in the crayfish, Procambarus clarkii, cutting of the nerves to 6 pereiopods is effective in shortening the interval between two ecdyses. In this species nerves to the pereiopods can be cut without the induction of autotomy.