ocellus

noun, plural o·cel·li [oh-sel-ahy] /oʊˈsɛl aɪ/.

1. a type of simple eye common to invertebrates, consisting of retinal cells, pigments, and nerve fibers.
2. an eyelike spot, as on a peacock feather.

noun plural -li (-laɪ)

1. the simple eye of insects and some other invertebrates, consisting basically of light-sensitive cells
2. any eyelike marking in animals, such as the eyespot on the tail feather of a peacock
3. botany
   1. an enlarged discoloured cell in a leaf
   2. a swelling on the sporangium of certain fungi

Plural ocelli (ō-sĕl′ī′)

1. A small, simple eye or eyespot, found in many invertebrates.
2. A marking that resembles an eye, as on the wings of some butterflies.