Photosensitivity in annelids-cnidarians-worms

Question

How photosensitivity in annelids, cnidarians and worms distinct from insects, cephalopods and vertebrates?

Answer 1

In the primary mentioned group of animals there are photoreceptors cells organized in ocelli or diffusely scattered in the body. Such animals do not form images.

In animals of the second group, the photoreceptor cells are element of more sophisticated structures, the eyes, capable to form images and to send them to nervous system.