Sponges are primitive animals without nervous systems or circulatory systems. Fossil records tell us that today’s sponges have ancestors dating back over 600 million years. Sponges are excellent water filters that draw water through their body walls into a central cavity, which is then pushed out of a large central chimney (osculum) by cells with a whip-like structure (flagellum). The flagellum is surrounded by tentacles that glean food particles from the moving water. This animal can filter a huge volume of water – about 100,000 times its size every day.