Snail mucus − glandular origin and composition in Helix pomatia

•The microanatomy of the Helix pedal gland system is described for the first time.•Histochemically, the dorsal and ventral glands mostly consist of acidic proteins and sugars such as mannose and fucose.•Two dorsal glands remain unreactive or synthesize acidic proteins only.•Helix pomatia differs from earlier descriptions of Helix aspersa regarding gland number and composition. Apart from their well-known culinary use, gastropod species such as Helix, which have a hydrogel-like mucus, are increasingly being exploited for cosmetic, bioengineering and medical applications. However, not only are the origin and composition of these “sticky” secretions far from being fully characterized, the number and morphology of the mucus glands involved is also uncertain. This study aims to characterize in detail the cutaneous glands of the Helix pomatia foot on morphological, histochemical and immunohistochemical levels. Hereby the focus is on the gland position and appearance on the foot sole as well as on the chemical nature of the different gland secretions. At least five different gland types can be distinguished by their microanatomy; three are located on the dorsal side and two on the ventral side of the foot sole. Most glands are reactive for acidic proteins and sugars such as mannose and fucose, indicating the presence of acidic glycosaminoglycans. One dorsal gland type shows high reactivity for acidic proteins only. The isolated mucus includes a certain amount of the elements chlorine, potassium and calcium; evidence for lipids was also confirmed in the isolated mucus. The present results for Helix pomatia show a clear difference in the number of glands compared to the related species Helix aspersa (only four mucus glands); histochemically, the glands of both species similarly produce acidic proteins as well as acidic glycosaminoglycans. While calcium ions are known to play a role in mucus formation, the presence and function of other ions such as potassium still need to be clarified.