Fine Structure of Supporting Elements of the Small Pit Organ in the Far Eastern Catfish, Silurus asotus

Abstract

The small pit organ of the catfish, Silurus asotus, was examined by electron microscopy. On the basis of their fine structures and positions in the organ, five types of cells were distinguished: 1) receptor cell (RC), 2) granular (supporting) cell (GC), 3) non-granular (supporting) cell (NGC), 4) mantle cell (MC), and 5) channel cell (CC). Both GCs and NGCs were located between the RCs in the sensory epithelium and had similar fine structures except for striking differences in their apical cytoplasm. The GC contained numerous secretory granules and scattered tonofilaments. By contrast, the NGC was characterized by abundant tonofilaments in their apical cytoplasm where only a small number of secretory granules were counted. The NGC always occurred in direct contact with RCs, whereas the GC never did so. The MCs, forming the outermost part of the organ, were characterized by numerous tonofilaments in the cytoplasm and resembled the ordinary epidermal cells in their fine structure. The CCs lined the duct of the organ, and con-tained electron dense cytoplasm and rather degenerative organelles. Presumably the GCs contribute to secretion of the mucous substance to the ampullary lumen, whereas the NGCs deal with nutrition and insulation for the RCs.