Comparison of gill surface morphology across a guild of suspension-feeding unionid bivalves

Freshwater mussels are found in dense, multi-species aggregations where the potential for resource partitioning should be high. One means by which mussels may be partitioning resources is through feeding on different food items. We compared gill morphology in four species of co-occurring freshwater mussels. We found differences in total gill surface area, density of latero-frontal cirri and the number of cilia per cirral plate, with one species, Actinonaias ligamentina, having the largest gills with densest cirral plates relative to the other three species. These differences in feeding structures might allow these species to utilize different food resources, or could be related to other functions performed by the gills, including respiration or brood storage.