Distribution of the turbellarian Urastoma cyprinae on the gills of the eastern oyster Crassostrea virginica

Urastoma cyprinae has been reported from the gills of various bivalve species. In Atlantic Canada, it has been identified in the eastern oyster Crassostrea virginica. Recent studies have demonstrated that U. cyprinae can cause serious alterations to gill tissue in mussels. It has been suggested that, in oysters, the worm feeds on mucus secreted by the gills. Our work has revealed that U. cyprinae is attracted to oysters and that the source of attraction is mucus. The current study focuses on the distribution of U. cyprinae on the gills of oysters in relation to the presence and the state of mucus from different regions of the gills. Findings demonstrate that the worms occur throughout the gill surface, but that they are most heavily concentrated along the basal food tract, the major pathway for the transport of food particles to the labial palps. If mucus plays an important role in the parasite's survival, then U. cyprinae's preference for this location may be a way of ensuring intimate contact between itself and the mucus slurry characterizing this site.