The pearleyes are a family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

, Scopelarchidae, of aulopiform

Aulopiformes

Aulopiformes is an 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 used for this group...

 fish

Fish

Fish are a paraphyletic group of organisms that consist of all gill-bearing aquatic vertebrate animals that lack limbs with digits. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish, as well as various extinct related groups...

es, distinguished by their unique visual system, with two retina

Retina

The vertebrate retina is a light-sensitive tissue lining the inner surface of the eye. The optics of the eye create an image of the visual world on the retina, which serves much the same function as the film in a camera. Light striking the retina initiates a cascade of chemical and electrical...

s in each eye.

They are small to medium fish, ranging in size from just 3.7 centimetres (1.5 in) in adult length to 35 centimetres (13.8 in) in length, depending on species. They have a similar appearance to lizardfishes, with a large mouth, numerous teeth, and a forked tail. The dorsal fin

Dorsal fin

A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...

 is located in the middle of the back, and there is also a small adipose fin.

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.

Pearleyes typically live between 500 metres (1,640.4 ft) and 1000 metres (3,280.8 ft), although some species may visit shallower waters during the night.

Species

The family Scopelarchidae contains 18 species, grouped into four genera:

Family Scopelarchidae

• Genus Benthalbella
  • Benthalbella dentata - Northern pearleye
  • Benthalbella elongata
  • Benthalbella infans - Zugmayer
    Erich Zugmayer
    Erich Johann Georg Zugmayer was an Austrian zoologist and ichthyologist-Species described by Zugmayer:* Benthalbella infans Zugmayer, 1911* Cetostoma regani Zugmayer, 1914...
    
    's pearleye
  • Benthalbella linguidens - Longfin pearleye
  • Benthalbella macropinna
• Genus Rosenblattichthys
  • Rosenblattichthys alatus - Winged pearleye
  • Rosenblattichthys hubbsi - Hubb's pearleye
  • Rosenblattichthys nemotoi
  • Rosenblattichthys volucris - Chubby pearleye
• Genus Scopelarchoides
  • Scopelarchoides climax
  • Scopelarchoides danae - Dana pearleye
  • Scopelarchoides kreffti - Twin-striped pearleye
  • Scopelarchoides nicholsi
  • Scopelarchoides signifer
• Genus Scopelarchus
  • Scopelarchus analis - Short fin pearleye
  • Scopelarchus guentheri - Staring pearleye
  • Scopelarchus michaelsarsi - Bigfin pearleye
  • Scopelarchus stephensi