The brownsnout spookfish Dolichopteryx longipes)1, a strange denizen of the deep, has been known for 120 years, but its amazing optics have only recently been worked out.

Even in clear water, sunlight is quickly absorbed with depth,2 so there is hardly any light at 1,000 m (3,000 ft). So creatures need special features to see in such minimal light. Many of them, including the spookfish, have tubular eyes that point upwards towards the surface. This is “like having a telescope on your head that points towards the surface”, according to Ron Douglas of the City University of London….

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