The blood system is a closed system, meaning that they have blood vessels through which the blood flows. There are two main longitudinal blood vessels, a dorsal one and a ventral one. These vessels have circular muscles around them which can contract rhythmically to keep the blood moving around the body. Blood flows from the head to the tail in the ventral vessel and back, from the tail to the head, in the dorsal vessel. The Rag worm has almost the same as a human in the way that the blood is all closed and it runs from the brain at the top to the bottom of the tail allowing the entire body to receive vital nutrients.