Ultrastructural characterisation of Marteilia species (Paramyxea) from Ostrea edulis, Mytilus edulis and Mytilus galloprovincialis in Europe

A focused ultrastructural study of Marteilia spp. found in cultured Ostrea edulis, Mytilus edulis and Mytilus galloprovincialis from France and Spain was conducted with emphasis placed on haplosporosomes, striated plate-like inclusions and spore wall morphology. Two types of haplosporosome were iden tified, sphaeroid and oblate, which were common to the parasite in all 3 ho st species. A total of 492 haplosporosomes were measured; those from the Ma rteilia sp. in Mytilus spp. were marginally smaller than those in Ostrea ed ulis. Spore wall morphology was found to vary depending on the state of mat urity of the parasite-the more mature the parasite, the thicker the wall su rrounding it. It is suggested that the current criteria used to distinguish M, maurini from M. refringens are invalid and that M. maurini was relegate d to a junior synonym of M. refringens.