The Sea Cucumber
The sea cucumber along with the starfish and the sea urchin has no brain. it has a ring of neural tissue that surrounds the oral cavity and sends nerves to the tentacles and the pharynx. The nerve ring does not however, play a large role in the nervous coordination since scientists have learned that if the ring is surgically removed, it can still move around and function. Five major nerves from the nerve ring, move down parallel to the body. Sea cucumbers have no distinct sensory organs although various nerve endings throughout the skin give it the sense of touch, and a sensitivity to the presence of light.