Many North American freshwater mollusks are at risk of extinction. Knowledge of basic ecology and systematics of the pleurocerid and hydrobiid gastropods is lacking. Pleurocerids are most diverse in southeastern USA, and we know that periphyton food limits their growth, and that their grazing, in turn, limits periphyton biomass. However, we know little about the effects of spates and current velocity on pleurocerid populations, and more work is needed to determine whether interspecific competition or significant risk from predation occurs. Hydrobiids are extremely diverse, but many species inhabit only a few springs (especially in arid western USA) and are at risk of extinction. More work is needed on their population and community ecology. Invasions pose a risk to native snail species. For example, the New Zealand mudsnail (Potamopyrgus antipodarum) interacts negatively with several hydrobiids in the Snake River in western USA. We suggest several research avenues that are needed if we are to maintain and restore pleurocerid and hydrobiid snail populations.