The histology and histochemistry of the pedal glandular system of two limpets, Patella vulgata and Acmaea tessulata (Gastropoda: Prosobranchia)

Patella vulgata possesses nine different pedal glands, six of which pour their secretions on to the sole. Proteins secreted by the marginal gland into the marginal groove are used for locomotion, especially when the limpet moves off following a period of adhesion. Another protein-secreting subepithelial gland, sparsely present throughout the foot, is also believed to be used in locomotion. A third gland type is present in the epithelium of the sole. The secretion of these epithelial mucocytes which is a weakly acidic muco-polysaccharide (MPS) is likely to have a locomotory function. Three other sole glands secrete highly viscous acidic MPS. Their secretions are likely to have an adhesive function. The three other glands present in the foot are contained within the side-wall. Of these, two are believed to secrete mucus to protect the animal against desiccation during emersion; and the other, present only in young P. vulgata , pours its acidic MPS secretion into the epipodial streak. This secretion consolidates debris before it is cleared from the pallial cavity; in adult animals, muscular contractions of the foot are powerful enough to clear debris without the help of the epipodial gland. In Acmaea tessulata the six glands present open out on to the sole and correspond in position, composition and function to the six glands of the sole of P. vulgata . There are no glands within the side-wall.