Induction of Extra Claws on the Chelipeds of a Crayfish, Procambarus clarkii

In a crayfish, Procambarus clarkii, growth of an extra claw was induced by making a V-shaped wound in the proximal end of the propodus of the second and third chelipeds. Two nerve bundles were damaged by the wounding. Some type of extra growth developed on the propodi of 13 of the damaged chelipeds: a pair of extra claws (2 chelipeds), a pair of extra dactyls (1 cheliped), a single extra dactyl (2 chelipeds), and a single slight projection (8 chelipeds). The extra claws and dactyls developed from the peripheral side of the propodus away from the wound site. One of a pair of extra dactyls and the single extra dactyls could be moved only slightly, either manually or by the crayfish. The other extra dactyls could be moved by the crayfish. Muscles were associated with each of the extra and primary claws. The muscles attached to the double extra claw or dactyl were innervated by nerve bundles that were branches from the primary thick nerve bundles. One possible explanation for these findings is that the severed nerve fibers in the thick nerve bundles regenerate, elongate into aberrant roots, and form extra claws or dactyls.