The Collaborative International Dictionary of English v.0.48:

Ocellus \O*cel"lus\, n.; pl. Ocelli. [L., dim. of oculus an
   eye.] (Zool.)
      (a) A little eye; a minute simple eye found in many
          invertebrates.
      (b) An eyelike spot of color, as those on the tail of the
          peacock.
          [1913 Webster]