Freshwater Sponge

Freshwater sponges are simple, sedentary animals found in lakes and slow rivers across much of the northern hemisphere. Spongilla lacustris forms encrusting or branching colonies on submerged rocks, logs, and vegetation, ranging in colour from green to brown depending on symbiotic algae and sediment. These sponges filter water through countless tiny pores, drawing in microscopic food; divers often spot them in cool, clear freshwater sites where currents are gentle. Colonies can persist through winter by forming hardy gemmules—dense clusters of cells that survive freezing and regenerate when water warms.