How does photosensitivity in cnidarians, annelids and worms differ from insects, cephalopods and vertebrates?
In the first mentioned group of animals there are photoreceptor cells organized in ocelli or diffusely dispersed in the body. These animals do not form images. In the animals of the second group the photoreceptor cells are part of more sophisticated structures, the eyes, able to form images and to send them to the nervous system
