Respiratory System
Sea Urchin Diagram
Sea urchins have a poorly developed respiratory system. Tube feet function as respiratory organs and tiny gills can sometimes be found on the skin. Tube feet are small tubular projections and are characteristics of the water vascular system.
Sea Urchin
Water travels into the tube foot through the outer pore, and exits back out through the inner pore. Water that has little oxygen and a lot of carbon dioxide travels in one direction inside the tube foot, while water that has a lot of oxygen and a small amount of carbon dioxide travels in the opposite direction outside the tube foot