Ocellus
plural OCELLI, in entomology and zoölogy, a spot within a ring of another color, like the pupil within the iris, except that the central spot is often surrounded by additional concentric zones. Example, the ocelli on the tail coverts of the peacock, and those on the wings of the peacock-butterfly. Ocelli, the simple eyes or stemmata of insects, generally situated on the crown of the head between the great compound eyes.
Used also of the simple eyes of spiders, crustaceans, mollusks, etc.