Echinoderms lack cephalization. what characteristics of this group emphasize the need for a head

The answer is: have simple receptors for light and chemicals are concentrated on the tips of the arms and sensory cells are scattered over the skin

Simple receptors and sensory cells that scattered over the skin indicate that those organisms need to transfer all the information that obtained by the receptors and sensory cells to other part of their bodies to be analyzed. For most organisms, this other part is the head where their brain is located.