Functional aspects of the mucus-producing glands of the Systellommatophoran slug, Veronicella floridana



The mucus-producing glands of the tropical slug Veronicella floridana Leidy were examined histochemically. The bulk of the dorsal mucus is a carboxylated mucopolysaccharide produced by deeply embedded gland cells which contribute to inflated common ducts. Little mucus is apparent on the dorsal surface of an unirritated slug, giving the dorsal aspect of the animal a dry appearance. Measurements of the rate of water loss of whole animals indicate that water is lost significantly more slowly than from the equivalent area of water.

The foot possesses regular transverse ridges and the pedal mucus is produced largely by a set of gland cells associated with each ridge. This mucus is a mixture of mucopolysaccharides and protein. The suprapedal gland which also contributes to the pedal mucus is extremely small and produces a weakly acidic and neutral mucopolysaccharide and a protein. There is no specialization in the leading edge of the foot and no Semper's organ. The cleft between the foot and the body is unciliated and bears few specialized gland cells.

Compared with the mucus produced by Limax pseudoflavus, the pedal mucus of Veronicella is of comparable function and composition though produced by glands of different derivations. The dorsal mucus is histochemically different from that of Limax though similar in physical appearance. Whilst the dorsal mucus of Limax is freely distributed over exposed surfaces, that of Veronicella is held in reserve in inflated ducts resulting in a dry leathery appearance and a depressed rate of water loss.