What is the difference between a closed and an open circulatory system?

Answer 1

In an open circulatory system, a tubular heart pumps hemolymph into a hemocoel (a system of interconnected sinuses), where chemical exchange can occur with the "bathed" tissues. The hemolymph diffuses back to the heart. This creates a sluggish blood flow because of low pressure & low oxygen content, resulting in low efficiency.

In a closed circulatory system, a muscular heart pumps blood into large vessels that branch into smaller vessels that course through the organs. The blood is confined to vessels and are distinct from the interstitial fluid.

Basically, an open circulatory system is somehow connected to the environment, while the closed circulatory system is just confined in the animal's body.

Answer 2

We, as vertebrates, have a closed system in that our blood travels from the heart and back. Other organisms don't have such a system. Open circulatory systems allow all fluids in an organism to mix.