A sponge is a simple aquatic animal that lives in oceans, rivers, and lakes. It has a porous body, which means it has many tiny holes that allow water to flow through. Sponges come in various shapes and colors, and they play an important role in the ecosystem by filtering water and providing habitats for other marine life, such as fish and crustaceans. Sponges are unique because they lack organs and tissues like most animals. Instead, they have specialized cells that help them absorb nutrients and oxygen from the water. Some sponges can even regenerate, meaning they can grow back parts of their body if they are damaged. This ability makes them fascinating creatures in the study of marine biology.