Localization of nadph-diaphorase-positive elements in the intestine of the mussel Crenomytilus grayanus (Mollusca: Bivalvia)

By NADPH-diaphorase histochemistry (Hope & Vincent, 1989), localization of nicotinamide adenine dinucleotide phosphate diaphorase-positive (NADPH-d-positive) elements was studied in the direct and recurrent loops of the midgut and hindgut of the mussel Crenomytilus grayanus. Intraepithelial NADPH-d-positive cells were found in the intestinal groove and major typhlosole of the direct loop and in the recurrent loop of the midgut, as well as in the hindgut. The cells are fusiform and lie separately or in minor groups. Their apical processes are directed to the gut lumen, and the basal processes contact with the basiepithelial plexus. The latter, in turn, sends separate NADPH-d-positive fibers to make contacts with subepithelial plexus. Both plexuses are well developed in the intestinal groove and major typhlosole of the direct loop and in the recurrent loop of the midgut, as well as in the hindgut. In the minor typhlosole and crystalline style sac, both plexuses are less developed. In the ciliary groove of the hindgut, the basiepithelial plexus is absent. Possible role of NADPH-d-positive elements in regulation of the digestion in bivalve mollusks is discussed.