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Sea anemones have a rather simple cardiovascular system. "breath" and circulate oxygen through the main opening in the middle, which is used as a mouth. Once inside, the oxygen, food, and materials are directly taken by the cells on the inside of the sea anemone. The cells on the outside absorb the oxygen, food, and materials directly from the water that they are in contact with. They have the same primitive "circulatory" system, which uses diffusion, The only difference is that that their source of oxygen is from the main mouth rather than collecting them from their outer layer.