Cell types in regenerating claws of the snapping shrimp, Alpheus heterochelis

Abstract

Cell types in the regenerating claws of adult snapping shrimps, Alpheus heterochelis, are described, based onelectron microscopy. Following autotomy of a limb, the coxal stump is secured by a membrane lined by a layer of proliferatingepithelial cells. Numerous fibroblasts with long cytoplasmic processes form small fluid-filled compartments that provide astructural framework and are inundated with mostly hemocytes and blood vessels. Agranular hemocytes are uncommoncompared with granular ones, which have prominent pseudopodia, vacuoles, and lysosomes, features that suggest a phagocyticfunction. The cytoplasmic network formed by fibroblasts persists in the regenerating blastema and papilla, together withgranular hemocytes and blastemal cells. Close structural associations were observed amongst all four cell types. Regionalproliferation of epithelial cells subdivides the distal tip of the papilla into the presumptive propus and dactyl and marks thebeginning of segmentation, which proceeds in a distal to proximal direction. This is accompanied by the appearance of firstafferent innervation, also proceeding in a distal to proximal direction, and multinucleate myoblasts identified by fragments ofmyofibrils, then efferent innervation and well-organized muscle. Prominent intercellular contacts between hemocytes and othercell types within the papilla may serve for adhesion as well as for communication. The early and prevalent appearance ofhemocytes in the regenerating limb bud, as well as their pluripotent nature in other regenerating tissues, implicates them as theorigin of blastemal cells.