Holochroal eye

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The Holochroal eye of Paralejurus sp.

Holochroal eyes are compound eyes with many tiny lenses (sometimes more than 15,000, each 30-100μm, rarely larger).[1] They are the oldest and most widespread type of trilobite eye,[2] and found in all orders of trilobite from the Cambrian to the Permian periods. Lenses show hexagonal close packing, and a single corneal membrane covered all lenses.[3] Unlike most modern arthropods, these eyes were not covered by the white layer known as the sclera.


  1. ^ Clarkson, E. N. K. (1979), "The Visual System of Trilobites.", Palaeontology 22: 1–22 
  2. ^ Schoenemann, B. (October 2007), "Trilobite Eyes and a New Type of Neural Superposition Eye in an Ancient System", Palaeontographica Abt. A (Verlag) 281 (1–3): 63–91 
  3. ^ Clarkson, E.N. (1997), "The Eye, Morphology, Function and Evolution", in Kaesler, R.L. (ed), Treatise on Invertebrate Paleontology, Part O, Arthropoda 1, Trilobita, revised. Volume 1: Introduction, Order Agnostida, Order Redlichiida, Boulder, CO & Lawrence, KA: The Geological Society of America, Inc. & The University of Kansas, pp. 114–132, ISBN 0-8137-3115-1