Telescopefish

The Giganturidae are slender, slightly tapered fish with large heads dominated by large, forward-pointing, telescoping eyes with large lenses. Their heads end in short, pointed snouts. The highly extensile mouth is lined with sharp, slightly recurved and downward-flexing teeth and it extends well past the eyes. The body lacks scales, but is covered in easily abraded, silvery guanine, which gives them a greenish to purplish iridescence in life. The gas bladder is absent and the stomach is highly elastic.

Telescopefish are presumed to be solitary, active predators, inhabiting the mesopelagic to bathypelagic zones of the water column from 500 to 3,000 metres (1,640 to 9,840 ft). By using their tubular, large-lensed eyes—which are adapted for optimal binocular light collection, at the expense of lateral vision—telescopefish are likely able to spy their prey's weak bioluminescence from a distance, as well as (by looking skyward) resolve the outlined silhouettes of prey against the gloom above. Their eyes may also help telescopefish to better judge distance of prey; these visual adaptations are typical of deep-sea fish (barrel-eye, tube-eye). Common prey include bristlemouths, lanternfish, and barbeled dragonfish.