Components of mucus of terrestrial slugs (Gastropoda)

Mucous secretion by the body wall of the terrestrial slugs (Ariolimax columbianus, Arionidae; and other species) was found to involve at least three distinct stages--release of vesicles, formation of granules, and organization of strands. Mucus is stored intracellularly in membrane-bound vesicles, and these are shed intact from the mucous cells. Disruption of the vesicle membrane, with release of contents, can be effected by endogenous lytic agent(s), as well as by exogenous surfactants, lipid solvents, or hypotonic media. Thereupon 1-micron granules are released. These may be stable, or they may change to material that is finely granular or in the form of strands; the transition to strands is facilitated by shear stress exerted through the fluid containing the mucous components. Lectins organize, or are organized with, the strands, as evidenced by agglutination of erythrocytes on them. Mucous formation, as seen in the living slug, differs markedly from the one-step process of exocytosis of fluid mucus inferred from studies of mucous membranes fixed for ultrastructural investigation.