Marteilia is a genus of Rhizaria that are parasites of bivalves. Species include Marteilia sydneyi, Marteilia refringens, and Marteilia cochillia. Marteilia refringens is a unicellular parasite affecting the digestive system of the flat oyster, Ostrea edulis. Other species that can be infected include the Australian mud oyster (O. angasi), the Argentinean oyster (O. puelchana), the Chilean flat oyster (O. chilensis), the blue mussel (Mytilus edulis) and the Mediterranean mussel (M. galloprovincialis). Early stages of the life cycle occur in the epithelia of the digestive ducts and possibly the gills of the host. Later the parasite migrates to the epithelial cells of the digestive tubules. There may be no symptoms of infection. The factors triggering a pathogenic response are unclear but ma