I just got back inside after picking a few dozen night crawlers for a fishing trip I’m going on this weekend. I never have figured why a critter who has no eyes can sense light . Those critters are quite quick retreatring into their hole when a light is shined on them.
How do night crawlers sense light?
I think they do have some sort of very rudimentry eyes. At least, a sensory system capable of “seeing” light and dark. They may also be able to pick up very slight tempature changes but I’m kind of WAG - ing here.
Not a direct answer, but this excerpt from the PBS series Evolution has some interesting information on eye development.
They do have some light sensory cells in their skins, although no ability to form a visual image. Less sensitive to the red end of the spectrum. Avoiding light is obviously a useful behavior for a creature that must avoid drying out or it will suffocate.
Many organisms have photoreceptors without having “eyes”.