Sponges are sessile organisms that attach to a firm substrate. There are about 30 species of freshwater sponges in North America, all belonging to the family Spongillidae. Sponges typically live in still waters, and are found regularly in larger rivers, lakes, wetlands, and in streams near lake outlets. They have simple bodies with no organs or differentiated tissues, but different cells in the colony play different roles. Freshwater sponge colonies have numerous microscopic holes through which water passes into the sponge, and a few large holes through which water leaves.
Sponges serve as food for a variety of other aquatic invertebrates, including caddisflies, midges, and spongillaflies. Sponges can reproduce sexually but are highly variable in the sex they choose to be. One may produce only male gametes one year and female gametes the next year. They can also multiply by starting a number of new colonies if fractured by disturbance, and they have a strong ability to regenerate.
The Xerces Society has profiled a rare freshwater sponge endemic to western Montana and known only from three lakes, Ephydatia cooperensis.