Common Freshwater Sponge

<em>Spongilla lacustris</em>, commonly known as the common freshwater sponge, is a sessile filter-feeding invertebrate belonging to the family Spongillidae. It is one of the few sponge species adapted to freshwater habitats, typically found in lakes, ponds, rivers, and streams across its range. This species has been documented in Belgium, Denmark, Norway, and Sweden, and is more broadly distributed across the Northern Hemisphere. <em>Spongilla lacustris</em> typically grows as irregular, encrusting masses on submerged rocks, logs, and aquatic vegetation, often taking on a greenish coloration due to symbiotic algae (zoochlorellae) living within its tissues. It filters microscopic organisms and organic particles from the water column, contributing to nutrient cycling in freshwater ecosystems. Biological traits of this species remain poorly documented in the scientific literature. The species typically reproduces both sexually and asexually, producing resistant structures called gemmules that allow it to survive harsh environmental conditions. Its presence is often associated with clear, unpolluted waters, making it a useful bioindicator of freshwater ecosystem health.