Answer:
Oxygen is moved around the body of an echinoderm in its C. water vascular system.
I believe is the thermoreceptors present in the skin as well as part of the brain called hypothalamus.
The answer is tissue fluid. Tissue fluid holds far smaller quantity of protein molecules because they are too large to escape easily over the tiny holes in the capillary endothelium. Tissue fluid doesn't contain red blood cells because they are too large, but does comprise some white blood cells.
