An Investigation into Nematodes Encapsulated in Shells of Wild, Farmed and Museum Specimens of Cornu aspersum and Helix pomatia

Nematodes are prolific and diverse parasites of gastropods that have evolved to use slugs and snails as definitive and intermediate hosts. Recently, several snail species have been shown to encapsulate and kill nematodes by encasing them in their shell under laboratory conditions. However, it is unknown how common this process is in wild populations. Also there has been little research on how the morphology and physiology of the shell may influence the successful identification of nematodes trapped in snails’ shells using molecular biology. We examined shells from several U.K. populations that consisted of wild Cornu aspersum from Formby and Littlebourne and farmed C. aspersum from Lurgan, as well as Helix pomatia from snail farms in France (Brumath and La Rivière Drugeon). We found nematodes present in shells collected from four out of five locations with the number of shells infected with nematodes ranging from 17% to 100%. Using previously described protocols we attempted to amplify nematode DNA from the shells with nematodes. Nematode DNA could be amplified from C. aspersum from Lurgan (as previously reported) but not from the other three snail populations. This could potentially be due to low starting numbers of nematodes in the shell and high calcium content prohibiting amplification of DNA. In a final experiment we discovered that museum collections of C. aspersum and H. pomatia had nematodes present in their shells that were over 100 years old. Taken together, these results show that C. aspersum and H. pomatia frequently trap and fix nematodes using their shell in wild and farm environments. However, in order for these nematodes to be identified successfully nematode infection load and calcium content should be considered.