Sporulation d'Haplosporidium sp. (Haplosporida, Haplosporidiiidae) chez l'huître Ostrea edulis L. du bassin d'Arcachon (France)

The life cycle of Haplosporidium sp., Haplosporida recently observed in the flat oyster of the bassin d'Arcachon (France), and the spore characteristics of which have already been presented (Pichot et al., 1979), has been studied by electron microscopy. The first stages of sporUïation are represented by two types of plasmodia. After the stage of sporonts, sporogenesis seems to develop according ,~ to two sequences. In a first sequence a cytoplasmic syncytium is formed, followed by the condensation of cytoplasm that would lead to the individualisation of uninucleate sporoblasts and anucleate cytoplasm fragments. The spores could result from the enclosing of the sporoblasts by the cytoplasmic fragments. In a second sequence the spores differenciation happens directly in the sporonts.