Ultrastructural description of the spore maturation stages of the clam parasite Minchinia tapetis (Vilela, 1951) (Haplosporida : Haplosporidiidae)

The fine structure of maturing spores of a haplosporidian parasite found in the gill, mantle and foot tissues of Ruditapes decussatus L. (Mollusca, Bi valvia), a species of commercial importance in Portugal, is described. When observed free in suspension, immature spores exhibit one or two epispore c ytoplasmic extensions (ECE) which constitute a projection of a portion of t he exosporoplasm, sometimes without ultrastructural organisation, surrounde d by the plasmalemma. Free spores observed by light microscopy (LM) after 3 -5 days of incubation in filtered sea-water exhibit no ECE attached to the spore wall. The mature spore is ovoid to ellipsoid, operculate, uninucleate and measures c. 4.8 mum long and c. 3.9 mum wide. The spore shape and size and the identity of the host living in the same geographical region sugges t that this species is the same as previously described using LM observatio ns as Haplosporidium tapetis Vilela, 1951 and later transferred to Minchini a Labbe, 1896.