All species have large, telescoping eyes which dominate and protrude from the skull, but are enclosed within a large transparent dome of soft tissue.[4] These eyes generally gaze upwards, but can also be directed forwards.[5] The opisthoproctid eye has a large lens and a retina with an exceptionally high complement of rod cells and a high density of rhodopsin (the "visual purple" pigment); there are no cone cells. To better serve their vision, barreleyes have large, dome-shaped transparent heads; this presumably allows the eyes to collect even more incident light and likely protects the sensitive eyes from the nematocyst (stinging cells) of the siphonophores from which it is believed the Barreleye steals food. It may also serve as an accessory lens (modulated by intrinsic or peripheral muscles), or refracts light with an index very close to seawater. A recent study disclosed that Dolichopteryx longipes is the only vertebrate known to use a mirror (as well as a lens) in its eyes for focusing images.[6]
The toothless mouth is small and terminal, ending in a pointed snout. As in related families (e.g. Argentinidae), there is an epibranchial or crumenal organ present behind the fourth gill arch. This organ—analogous to the gizzard—consists of a small diverticulum (pouch) wherein the gill rakers insert and interdigitate for the purpose of grinding up ingested material. The living body of most species is a dark brown covered in large, silvery imbricate scales; but these are absent in Dolichopteryx, leaving the body itself a transparent white. In all species a variable number of dark melanophores colour the muzzle, ventral surface, and midline.

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