The Barreleyes (A.k.a the The Glasshead Fish) is one of the most mysterious marine creatures known to science.
Its length is no more than 15 cm, and it lives at a depth of about 2.5 kilometers.
The body of the fish is completely transparent gelatin that allows us to see his internal organs.
The translucent skull is not just an interesting fashion statement, but a vital feature for the fish. Because of his see-through skull cap, he can absorb the little light that sleeps to this abyss. There are two black circles that look like cute eyes, well, Contrary to what had been thought in the past, these are not the eyes but it is the fish’s nostrils. The eyes are the pair of green balls that are in his skull cap which named the fish Barreleyes due to their barrel-shape. The light comes through his transparent skull and the eyes of the fish can rotate 90 degrees, so it can look up.
Its source of food is jellyfish, but in this case jellyfish are only the source and not the food itself – the fish feeds on the plankton around jellyfishes bodies, and it does not harm the jellyfish themselves.
The gelatin that makes up his body is very soft, and a slight contact with any object is enough to tear this layer and kill the fish, so the seabed is probably the only safe place where it can dwell.
The existence of the fish has been known since 1939, but until 2004, only the dead bodies were found via fishing nets. The only (so far – 2017) shot of a live Barreleyes fish was taken by marine biologists Bruce Robison and Kim Reisenbichler which took the video by an unmanned, undersea RC robot.