Barreleye fish shows a transparent head..

Barreleyes share their deep-sea environment with many different types of jellies. Some of the most common are siphonophores (colonial jellies) in the genus Apolemia. These siphonophores grow to over 10 meters (33 feet) long. Like living drift nets, they trail thousands of stinging tentacles, which capture copepods and other small animals. The researchers speculate that barreleyes may maneuver carefully among the siphonophore’s tentacles, picking off the captured organisms. The fish’s eyes would rotate to help the fish keep its “eyes on the prize,” while its transparent shield would protect the fish’s eyes from the siphonophore’s stinging cells.