Organization of the nematocyst battery in the tentacle of hydra: Arrangement of the complex anchoring junctions between nematocytes, epithelial cells, and basement membrane

Abstract

Nematocytes (stinging cells) of hydra tentacles are anchored to the basement membrane by peculiar complex junctions in which a flattened tongue of an epithelial cell is interposed between the nematocyte and the basement membrane. In this paper we describe the arrangement of these junctions with emphasis on how they are related to the architecture of the epithelial cell. Each epithelial cell, called a battery cell, harbors 10–20 nematocytes and bears muscle processes that extend along the basement membrane. The epithelial cell component of the complex junction is usually a lateral extension of a muscle process. All nematocytes within a battery cell make junctions with muscle processes of the same (“resident”) epithelial battery cell despite the presence of numerous muscle processes from adjacent (“foreign”) cells. Some nematocytes make junctions with several resident processes, spanning the foreign processes to do so. Most junctions reside near the proximal ends of the muscle processes. New findings are reported on the substructure of the junctions. They are composed of aggregates of smaller elements, and the cytoskeleton within the complexes has a pronounced longitudinal organization. These observations are consistent with a suggestion that the complex junctions develop by aggregation of smaller junctional units originating elsewhere on the cells.