Respiratory pigments (呼吸色素), proteins that transport oxygen, greatly increase the amount of oxygen that blood can carry • Arthropods (節肢動物) and many molluscs (軟體動物) have hemocyanin (血青素) with copper as the oxygen-binding component • Most vertebrates and some invertebrates use hemoglobin (血紅素) • Myoglobin (肌紅素) , a molecule found within muscle cells, stores oxygen for use by the mitochondria of muscle cells and imparts the characteristic red color to muscle.