Unique eye of probable evolutionary significance.

@article{Eakin1981UniqueEO,
  title={Unique eye of probable evolutionary significance.},
  author={Richard M. Eakin and J L Brandenberger},
  journal={Science},
  year={1981},
  volume={211 4487},
  pages={1189-90}
}
The eyes in the brain of a larval flatworm studied by electron microscopy are dissimilar. Light-sensitive structures in the right eye are microvilli; those in the left eye, the unique one, are both microvillar and ciliary. Perhaps this is evidence for the origin of a microvillar line of photoreceptoral evolution from a more primitive ciliary line.