Abstract

Spores of a microsporidian parasite were found in the queen scallop, Aequipecten opercularis (L.), collected from several coastal sites around the United Kingdom. Developing spore stages were detected in contact with the host cell cytoplasm. Infected host cells formed aggregates in the connective tissue of the digestive gland. Fully mature spores were found free within blood vessels. These spores exhibited a dome-shaped polaroplast, a diplokaryon, a posterior vacuole, and an isofilar polar tube, with seven to eight coils in a single row. In immature spores, the number of coils in the polar tube varied, with some having 7 to 8 coils and others having 10 to 12 coils.