Ultrastructure of the Spore of Haplosporidium lusitanicum sp. n. (Haplosporida, Haplosporidiidae), Parasite of a Marine Mollusc

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Abstract
The fine structure of H. lusitanicum sp. nov., a haplosporidian parasite found in the visceral tissues of Helcion pellucidus (Gastropoda; Prosobranchia) has been described. Spores were ellipsoidal, .apprx. 3.0 .times. 2 .mu.m, and surrounded by a proteinaceous wall .apprx. 0.1 .mu.m thick. The apical zone of the wall was modified into a complex opercular system covering a circular orifice .apprx. 0.5 .mu.m in diameter. The oval operculum consisted of a lid, .apprx. 2.2 .times. .apprx. 1.5 .mu.m and has oval shape, connected by a hinge to the wall in a limited zone. In the basal region, the wall is thicker and gives rise to 2 long tape-like proteinaceous filaments, each .apprx. 112 .mu.m long. The very dense endosporoplasm contained a basal, single nucleus, a complex membranous structure (spherule), a few mitochondria, several haplosporosomes and several vesicles. Cytochemical analysis by silver proteinate (Thiery''s method) revealed that the middle electron-light layer of the wall, and the vesicles of the spores, acquire a dark deposit characteristic of polysaccharides. The characteristics of spore wall structure, spore shape and size, number and dimension of tape-like filaments, and the identity of the host suggest that the parasite is a new species, which is herein designated H. lusitanicum (Portugal = Lusitania).