Ocellus

n. eye common to invertebrates; eye-shaped spot

An ocellus (plural: ocelli) is a type of photoreceptor organ in animals. Also called "simple eyes", ocelli are miniature eyes capable of sensing light but not distinguishing its direction. See also stemmata, which are structurally similar. Ocelli are found in many invertebrates. Insects in particular have two types of ocelli, dorsal ocelli and lateral ocelli.
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Noun
1. an eye having a single lens
(synonym) simple eye, stemma
(hypernym) eye, oculus, optic
(hyponym) ommatidium
2. an eyelike marking (as on the wings of some butterflies); usually a spot of color inside a ring of another color
(synonym) eyespot
(hypernym) marking

(n.)
An eyelike spot of color, as those on the tail of the peacock.
  

(n.)
A little eye; a minute simple eye found in many invertebrates.
  

N M
(little) eye; darling