A deep-sea fish with a transparent head and tubular, barrel-shaped eyes that point upward.
From barrel (describing the shape) plus eye, combining descriptive English words. The term was coined by scientists in the 1800s when the fish was first described, as its unusual eye structure resembled a barrel standing upright.
The barreleye fish lives in complete darkness thousands of feet below the ocean surface with eyes so specialized they can only look up at the silhouettes of prey against faint light from above—it's like having two telescope lenses pointed at the sky. Its transparent head was so strange that scientists initially thought they were looking at a different species depending on angle.
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