Barrel-eye Opisthoproctus soleatus
Many fish that live in the twilight zone, including the barrel-eye, have large eyes to make full use of what little light is available. As well as being large, the eyes of this species are tubular and point upward. This arrangement probably helps the barrel-eye to stalk other fish from below. Looking up, it is likely that the barrel-eye can pick out the silhouette of its prey or spot fish with bioluminescent patches on their undersides.