Final answer:
Planarians have eyespots that detect light and chemical gradients, contributing to navigation and food location. Their simple nervous system includes a cluster of nerves and sensory cells at the front end.
Step-by-step explanation:
Planarians do not have true eyes; instead, they have eyespots that sense changes in light and chemical gradients. These eyespots, also known as ocelli, are simple sensory structures that can only detect light in their environment, helping the planarian to navigate and find food.
The nervous system of planarians is relatively simple, with a concentration of nerves and clusters of photosensory and chemosensory cells at the anterior end, which includes the eyespots. This arrangement is part of a ladder-like nervous system, featuring interconnected nerve cords running the length of the body and contributing to the planarian's sensory perception.