Barreleye fish
Depth: 750 m · Twilight Zone
The barreleye fish has a see-through head like a glass dome. Inside sit two glowing green tube-shaped eyes that look straight up through its own skull, so it can spot faintly glowing prey drifting above it.
For scientists
Macropinna microstoma can rotate its tubular eyes from looking straight up to looking forward, so it keeps spotted prey in view as it snaps. The clear fluid-filled dome over its head shields the eyes and gathers what little light remains. The fish probably steals prey from the stinging threads of siphonophores, which is why looking up through its own head is so useful.
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