A coral polyp is, in some sense, literally only a stomach with neurons and muscles. They have little tentacles that float in the water, waiting for small organisms to swim toward them. When food touches one of the tips of these tentacles, they rapidly contract, pulling the prey into the stomach cavity where it is digested. Neurons on the tips of these tentacles detect food and trigger a cascade of signaling through a web of other neurons that generates a coordinated relaxing and contracting of different muscles.
