Nervous System of Asteroidea
The nervous system of steroids is not ganglionated and is closely related with epidermis. It consists mainly of a circumoral nerve ring surrounding the mouth. From this nerve ring radial nerves expand into each arm. The radial nerve supplies branches to the podia and ampullae and is continuous along with the subepidermal nerve net. Sense organs in asteroids are the eye spots found at the tip of the arm. The epidermis has as well sensory cells that probably function like photoreceptors, chemoreceptors and mechanoreceptors. The epidermal sensory cells are much more prevalent on the suckers of tube feet, tentacle like sensory the feet and along the margins of the ambulacral groove.