Patella ulyssiponensis is parasitised by Cercaria patellae, a trematode platyhelminth, which have infection levels of 5-10% in adults and can cause damage of the digestive gland. Gymnophallid metacercariae infect between the mantle and the shell and have an infection level of approximately 5%. The gut of Patella ulyssiponensis is sometimes infected by larval cyclophyllidean tapeworms (Kinne, 1980).