In the animal kingdom, the phylum of molluscs is the second in size, after that of the arthropods, with about 100,000 species from fossil (40,000) and living (60,000) varieties. Snails are part of the group of lunged gastropods, that is terrestrial molluscs, which do not have gills, but a lung structure that has allowed them to colonize air environments.
As well as many other animal and plant species, snails have also been overwhelmed by the consequences of human actions. The causes of the threat are many: the use of harmful pesticides, rampant urbanization, regimentation of river banks, uncontrolled water extraction or introduction of alien species are all factors that together have caused the gradual destruction of habitats.