Sponges (Porifera) are a group of animals that includes about 10,000 living species. Members of this group include glass sponges, demosponges, and calcareous sponges. Adult sponges are sessile animals that live attached to hard rocky surfaces, shells, or submerged objects. The larvae are ciliated, free-swimming creatures. Most sponges inhabit marine environments but a few species live in freshwater habitats.