eyespot

Short definition from Wiktionary

Noun

1. 1
   Any of various primitive light-sensitive organs or regions in many diverse organisms.
2. 2
   An eye-like marking on the tail of a peacock or the wing of a butterfly.
3. 3
   A coloured spot in a motile gamete or spore, which is sensitive to light.
4. 4
   Any of a group of fungal infections of grasses that are characterized by oval spots; strawbreaker.