Glasshead Barreleye Fish Has Previously Unknown Type of Eye With Two Retinas

Posted on March 21, 2014

Researchers from The University of T´┐Żbingen's Institute of Anatomy has discovered a fish with a previously unknown type of eye. The glasshead barreleye fish (rhynchohyalus natalensis) is found at depths of 800 to 1000 meters. The fish has a cylindrical eye pointing upwards. It also has a mirror-like second lens and retina that can detect bioluminescent flashes to the sides and below. The fish can see objects above it with its conventional cylindrical eye and detect other deep-sea creatures to the side and below with its reflector eye looking sideways.

Professor Hans-Joachim Wagner reports on the unusual fish eye in the journal, Proceedings of the Royal Society. Wanger says another fish, the sea brownsnout spookfish, also uses a combination of reflective and refractive lenses in its eyes. However, the optics of the diverticular eyes in the two fish species differ and developed differently.

Laser Focus World has a diagram here that shows how the eye's mirror and refractive lens system works and enables the glasshead barreleye fish to see predators above it as well as to the side and below it.

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