Composition of external setae during regeneration and transformation of the bilaterally asymmetric claws of the snapping shrimp,Alpheus heterochelis

The paired thoracic chelipeds or claws of adult snapping shrimp, Alpheus heterochelis, are bilaterally asymmetric, consisting of an enlarged and elaborate, sound-producing major (snapper) claw and a much smaller minor (pincer) claw. These paired claws vary in the composition of their external sensilla. Both possess long serrulate and simple short setae but the snapper also have plumose setae and long serrulate setae on the plunger. The pincers differ in having short serrulate setae and, in males alone, a prominent fringe of plumoserrate setae. During regeneration of each claw type, these setal structures are gradually added over three molts to reach the pristine condition. The long serrulate and simple short setae appear first, being seen in intermolt limb buds and commonly in both claws. Setae exclusive to each claw, i.e., plumoserrate and short serrulate in the pincer and plumose and long serrulate on the plunger in the snapper, appear sparsely in either the regenerated 1st or 2nd postmolt claw, they proliferate in the subsequent 2nd or 3rd postmolt claw. Transformation of the pincer claw to the snapper type begins in the 1st postmolt stage with the loss of pincer setae and addition of snapper setae and is completed by the 3rd postmolt stage. Since changes in composition of the external sensilla are restricted to postmolt stages, the underlying hypodermis is presumably being remodeled during proecdysis.