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In invertebrates like earthworms and leeches, hemolymph (a fluid analogous to blood) circulates via waves of muscular contractions. Unlike vertebrate blood, hemolymph bathes tissues directly within open spaces, aided by structures such as the heart muscles, which propel the fluid.
Some invertebrates also contain hemocyanin—a copper-based oxygen transport protein, similar to hemoglobin in humans—that facilitates oxygen transport in hemolymph.
Circulatory Pathways in Vertebrates
Vertebrate circulatory systems are more complex, featuring chambers such as atria and ventricles, along with valves that regulate blood flow.