Marteilia

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 may be related to environmental stress. The gross signs of marteiliosis include the visceral tissues losing their pigmentation and becoming pale yellow. In some cases the mantle become translucent and shell growth may cease. Affected shellfish can become emaciated and in heavy infections tissues appear shrunken and slimy. Mortality seems to be related to the sporulation of the parasite. The parasite was first observed in France in 1979 and has since spread to other countries in Europe.