The pearleyes are a

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

, Scopelarchidae, of

aulopiform Aulopiformes is a diverse order of marine ray-finned fish consisting of some 15 extant and several prehistoric families with about 45 genera and over 230 species. The common names grinners, lizardfishes and allies, or aulopiforms are sometimes ...

ray-finned fish Actinopterygii (; ), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish that comprise over 50% of living vertebrate species. They are so called because of their lightly built fins made of webbings of sk ...

, distinguished by their unique visual system, with two

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

s in each eye. They are small to medium fish, ranging in size from just in adult length to in length, depending on species. They have a similar appearance to

lizardfish The Synodontidae or lizardfishes(or typical lizardfish to distinguish them from the Bathysauridae and Pseudotrichonotidae) are benthic (bottom-dwelling) marine and estuarine bony fishes that belong to the aulopiform fish order, a diverse grou ...

es, with a large mouth, numerous teeth, and a forked tail. The

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

is located in the middle of the back, with a small

adipose fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only b ...

. Like many other deep-sea fish, their eyes are telescopic, allowing them to see in near darkness. However, unlike any other fishes, their eyes also possess a "pearl organ"; a white spot on the surface of the eye that may help to pick up light from the side of the fish, out of the normal visual field. The pearl organ is associated with a secondary retina, allowing the fish an unusually wide field of view. Specifically, pearleyes can see up to 20 degrees below the horizontal despite the nearly 40-degree angle created by the tubular eyes of the pearleye above the horizontal. While the majority of pearleye species are found in tropical waters, pearleyes have been found in every ocean in the world, including the ''Lagiacrusichthys,'' a newly described genus found in the Antarctic Ocean.Davis, M. P., (2015). Evolutionary Relationships of Deep-Sea Pearleyes (Aulopiformes: Scopelarchidae) and a New Genus of Pearleye from Antarctic Waters. ''Copeia'', 103(1), pp 64–71. doi.org/10.1643/CI-14-139 Pearleyes typically live between , although some species may visit shallower waters during the night.

References

{{Taxonbar, from=Q1501875