Scientists found the Pacific barreleye can swivel its tubular eyes forward by up to 75°, letting the 15cm fish line up prey before plucking it with its small mouth.
At 600–800 meters in the North Pacific twilight zone, the fish usually points those eyes upward to catch faint silhouettes and bioluminescent signals from siphonophores and trapped prey.
The transparent, fluid-filled head houses the eyes inside a protective dome, giving them room to rotate while shielding delicate tissues from the stinging cells of its targets.
Early specimens collected in 1939 were badly distorted by capture trauma and pressure change, and only live observations in 2004 and 2008 revealed the fish's true head structure and eye movement.