Under the direction of Dr. Caryn Vaughn, I have been examining differences in gill ultrastructure among four freshwater mussel species using scanning electron microscopy. Mussels use their inhalant siphon to pump water into their mantle cavity where the water is then drawn over the mussel's filter feeding organs, its gills. Cilia, arranged in fused sets of cirral plates, are used to capture food particles like a seive. We are finding that co-occuring mussel species differ in both cirral plate density and number of cilia per cirral plate, suggesting that species might differ in their ability to select algal and bacterial particles from the water. (Photo: cirral plates of Actinonaias ligamentina)