Ehinodermata
Starfish- Starfish do not have a true circulation system. But circulation still occurs in three places in a starfish. The perivisceral coelom is basically, the space inside the body but outside the various organ, the hemal system, and the water vascular system. The hemal system is most like the circulatory system. There are hemal channels forming three rings that are connected by the axial sinus. There are also radial hemal channels running down the rays next to the gonads. A dorsal sac attached to the axial sinus pulsates, sort of like a very inefficient heart because it lacks a one-way valve system. The hemal system seems mostly organized to distribute nutrients from the digestive tract.
Sea Urchin- Sea Urchins have closed circulatory systems. As with other echinoderms, sea urchins don't have a brain and instead rely on their water-vascular system which is like a circulatory system and comprises of water-filled channels that run through the body of the sea urchin.
Sea Cucumber- A sea cucumber has a closed circulatory system. The blood vascular system of a sea cucumber consists of two major vessels. The dorsal vessel pumps colorless blood that goes to the vessels within the walls of the intestine into the ventral vessel. Two places where there is circulation are the lower region of the small intestine and the upper region where blood is pumped by single chambered hearts.
How the Sea Star uses water vascular system: http://www.youtube.com/watch?v=CoSCUiQauKw
Sea Urchin- Sea Urchins have closed circulatory systems. As with other echinoderms, sea urchins don't have a brain and instead rely on their water-vascular system which is like a circulatory system and comprises of water-filled channels that run through the body of the sea urchin.
Sea Cucumber- A sea cucumber has a closed circulatory system. The blood vascular system of a sea cucumber consists of two major vessels. The dorsal vessel pumps colorless blood that goes to the vessels within the walls of the intestine into the ventral vessel. Two places where there is circulation are the lower region of the small intestine and the upper region where blood is pumped by single chambered hearts.
How the Sea Star uses water vascular system: http://www.youtube.com/watch?v=CoSCUiQauKw