Echinodermata
Echinodermata is a phylum of strictly marine animals. This phylum includes Starfish, Sand Dollars, and Sea Cucumbers. Echinodermata do not contain a circulatory system similar to humans. All echinodermata have a system called the water vascular system. The water vascular system simply circulates sea water through the echinoderm. The water vascular system enables the echinoderm to move, transport waste and water, and aids in respiration. Echinoderms do not have a true heart.
Here is a cool video that explains the water vascular system, specifically in starfish.
Here is a cool video that explains the water vascular system, specifically in starfish.