Transport Structures and Mechanisms Another important organ system in the worm is the circulatory system. The earthworm, like some invertebrates, has a closed circulatory system. This means that the blood is closed at all times within vessels of different size and wall thickness – blood is pumped by a heart through vessels, and does not normally fill body cavities. The earthworm circulates blood exclusively through vessels. Within the earthworm there are three main vessels that supply the blood to the organs around their body. These vessels are; the aortic arches, dorsal blood vessels and the ventral blood vessels. The aortic heart of the worm functions like a human heart. There are five pairs of aortic arches which all have the responsibility if pumping blood into the dorsal and ventral blood vessels. Blood is carries to the front of the earthworm’s body through the dorsal blood vessels. The ventral blood vessels are responsible for carrying blood to the back of the earthworm’s body. (Merriam Webster, n.d.) Part C: Compare and Contrast the Different Mechanisms ¾ Page NUTRITION:>