| Abstract: | The ultrastructural study of the ventral pair mucous gland (VPMG) of the foot of Mytilus galloprovincialis shows the presence of two cell types (type I and II cells) characterized by the cytoarchitecture typical of mucous secreting cells and distinct for the different structure of their secretory granules. The cytochemical tests performed on semithin (1 micron) and ultrathin sections show that type I secretory granules are made up of proteinaceous nucleoids and of a microfilamentous matrix containing both carboxylated and sulphated glycosaminoglycans. Type II secretory granules are mainly formed by glycoproteins. The ultrastructural and cytochemical studies do not support the hypothesis that VPMG secretions directly contribute to the formation of byssus threads. It is more probable that such secretions provide a protective and lubricating blanket during the multistep process of secretion, moulding and extrusion of byssus threads. |
