a family of freshwater invertebrates of the order Keratosa. Found on underwater objects in the form of irregular or treelike overgrowths 1 m high. Their color is green, yellow, or cinnamon-brown. The skeleton consists of siliceous spicules connected by an organic substance called spongin. The Spongillidae are widespread throughout the world. Sixteen genera are known; of these, four live in the rivers and lakes of the USSR. They reproduce either sexually or by budding. In the temperate zone the sponges die off, forming a large number of so-called winter buds or gemmules—spherical bodies (less than 1 mm in diameter) enclosed in a strong protective membrane. In the spring the gemmules germinate into young sponges. Spongillidae may do harm by settling in water pipes and clogging them. Powder made from dry Spongillidae is a popular remedy rubbed into the skin in the form of ointment for rheumatic and other pains.