This is a photograph of Macropinna microstoma, also called barreleyes. It has a very peculiar optical arrangement. When you first look at this photo, you may think the two small ovals above and behind its mouth are the eyes, and that it looks rather sad…wrong. Those are its nostrils. The eyes are actually the two strange fluorescent green objects that look like they are imbedded in its transparent, dome-like head.
It gets the name “barreleyes” because it’s are cylindrical, rather than spherical; this is an adaptation for better light collection in the dim depths where it lives, using very large lenses but not building a giant spherical eye to compensate. It’s ore like a telescope than a wide-angle camera. Here’s what a single eye in a side view looks like — the lens (L) is what is glowing so greenly in the photos.
As if that weren’t weird enough, the animal has a completely transparent skull cap, and the eyes swivel about within the skull to look out through that translucent cranium. In the two pictures below, the animal is first looking straight up through its head (the eyes are in the same orientation as in the diagram above), and in the right frame it has rotated the binocular-shaped eyes forward to look ahead.
Nature is always coming up with something stranger than we would imagine, and Macropinna is a perfect example. Apparently, the function of this arrangement is to give the animal a sensitive light detector for tracking its prey, bioluminescent jellyfish, and at the same time to shield the eyes from the stinging tentacles of the jelly while it’s eating it.
Robison BH, Reisenbichler KR (2008) Macropinna microstoma and the Paradox of Its Tubular Eyes. Copeia 2008(4):780-784.