The Class Demospongiae is the largest class of sponges, comprising about 90% of all sponge species. They are mostly marine, though some live in freshwater, and have skeletons made of spongin fibers, silica spicules, or both. Demosponges exhibit a wide range of shapes and sizes, with complex canal systems for filtering water to obtain food. They play important ecological roles by filtering large volumes of water, providing habitat for other organisms, and contributing to nutrient cycling in aquatic ecosystems.