The Giant Clam has an open circulatory system. This means that their blood does not travel through veins or arteries. The blood just goes directly to the clams organs. The blood traveled through open sinuses in the body. The blood travels through the heart, passing by the digestive system, and it is after that when the nutrients are picked up. Then, the blood travels through the gills where oxygen is distributed into the blood flow. Every time the heart beats, it pulls oxygenated hemolymph inside of the gills. It then travels to the heart. This is the only part of the clam’s circulatory system that is closed.