While a starfish lacks a centralized brain, it has a complex nervous system with a nerve ring around the mouth and a radial nerve running along the ambulacral region of each arm parallel to the radial canal.
22.
In " Caenorhabditis elegans ", the snt-1 gene ( C22orf25 homologue ) was expressed in the nerve ring, ventral and dorsal cord processes, sites of neuromuscular junctions, and in neurons.
