Description of Haplosporidium edule n. sp (Phylum Haplosporidia), a parasite of Cerastoderma edule (Mollusca, Bivalvia) with complex spore ornamentation

A new haplosporidian Haplosporidium edule sp. n. is described from the digestive gland tissue of the cockle Cerastoderma edule collected in Galicia (Northwestern Spain). The fine structure of the spores, mainly their surrounding ornaments attached to the spore wall, are described from light, scanning and transmission electron micrographs. Plasmodial development and sporoblast formation phases of the life cycle were observed. The spores were ovoid to ellipsoidal (3.20 x 2.20 mum) and the apical zone of the wall modified into a complex opercular system covering a circular orifice 0.5-0.8 pm in diameter. The spore wall (0.10-0.12 mum thick) was composed of inner (similar to70 nm), middle (similar to15 nm) and outer (similar to30 nm) layers. The electron-dense material that forms the outer layer was extended into numerous surrounding folds and slender projections (up 38 in number were counted in SEM). The surrounding folds were arranged in parallel and perpendicular to the spore axis. The slender projections were about 1.2 mum (range 0.8-1.5 mum) (n = 50) long with a diameter of about 70-90 nm as measured in SEM and in ultrathin transverse sections. Each projection had a bifurcated tip, with branches about 0.25-0.30 mum in length. The projections emerged from the spore wall among the folds. The taxonomic affinities of the new species are discussed and morphological comparisons made, mainly with the spore ornamentation of other similar species of the same genus.