These auricles contain chemoreceptors that are used to find food. The ocelli are sensitive to light and are connected to the cerebral ganglia. Generally, the flatworm avoids light. If the first ventral ganglion is removed, the earthworm will stop eating and will not dig. Each segmented ganglion gets sensory information from only a local region of its body and controls muscles only in this local region.
Earthworms have touch, light, vibration and chemical receptors all along the entire body surface.
The nervous system is characterized by a nerve ring that surrounds the mouth. A radial nerve branches off of the nerve ring and extends to each arm. The picture on the left shows one of 3 nerve nets that extend throughout the body. Starfish have an interesting way of detecting light. The eyespot contains light sensitive pigments that allow the starfish to detect shadows and changes in the brightness of light.