Greetings steemians and welcome to another daily post of my strange animals series. Today I have for you a truly bizarre freak of nature, the Pacific Barreleye, a deep sea fish best known for its transparent head!

Scientifically described as Macropinna microstoma, this animal takes its name after the large, barrel shaped eyes it has.

Pacific barreleye fish (credit)

Now, let's learn more about it!

What's the deal with the transparent head?

First, I want you to take a good look at the creature's eyes in the photo above. Now, take a good look again because what you are probably looking at is the eye-like olfactory organs (called nares) on the front of its face, which are analogous to nostrils ! The eyes, capped by bright green lenses, actually reside inside the head!

Since its discovery in 1939, biologists guessed that the tubular eyes are very good at collecting light, a very useful trait to have when living in the deep dark ocean. Up until very recently, the eyes were believed to be fixed in place, providing only a tunnel-like view of what is above the head. However, a study published in 2008 revealed that the eyes can actually rotate inside the head, allowing the fish to look at multiple directions.

To be technically correct though, the eyes don't reside inside the head, but within "a transparent shield that covers the top of the head and may provide protection for the eyes from the tentacles of cnidarians." [1]

This transparent, fluid-filled shield that covers the top of the head was an unknown feature of the species and was revealed by a ROV video by the Monterey Bay Aquarium Research Institute (MBARI).

Are you ready for a treat? The video I am talking about is available online. Enjoy:

https://www.youtube.com/watch?v=RM9o4VnfHJU

But why did this feature remain unknown for so long?

Most of the things we knew about the barreleye fish was from research done on dead specimens caught in nets. Unfortunately, all of them were in bad condition with the transparent dome destroyed.

Captured specimen, with the membrane shield destroyed. (credit)

However, Robison and Reisenbichler from the aforementioned study, examined these creatures in their natural habitat with the help of remotely operated vehicles mounted with cameras.

It's thanks to the videos these two took at depths of up to a half-mile below the surface, that we now know about the transparent head of the fish. They even managed to capture a live specimen with the shield intact and examined it for several hours in a shipboard aquarium.

But the weirdness doesn't stop here!

The weirdness of this fish doesn't stop at its transparent head, as they have come up with some other cool adaptations for their deep-sea life. Here's what the scientists responsible for the discovery of the shield had to to say:

"Their large, flat fins allow them to remain nearly motionless in the water, and to maneuver very precisely (much like MBARI’s ROVs). Their small mouths suggest that they can be very precise and selective in capturing small prey. On the other hand, their digestive systems are very large, which suggests that they can eat a variety of small drifting animals as well as jellies. In fact, the stomachs of the two net-caught fish contained fragments of jellies. " [2]

Some Closing Thoughts

Despite the recent discoveries, the Pacific Barreleye remains hugely a mystery, with many questions surrounding its existence. Hopefully, the advancement in ROV technology will provide us with some answers in the future!

I will close this article with some quick facts about this unique creature. If you want to learn more about it, I suggest you to visit the links in the references. But I think I have covered all the basics and there isn't much else to know other than technicalities.

Some Quick Facts

The Barreleye fish was first discovered by the marine biologist, Chapman in 1939
Most specimens caught in nets are about 15 cm long. The larger ever caught was about 45 cm
The green pigments in the eyes filter out sunlight that comes directly from the sea surface, helping the fish to spot the bioluminescent light that many jellies and other aquatic creatures emit.
They are solitary and spend most of their life motionless, with the body in a horizontal position and the eyes looking upward.

References

Macropinna microstoma and the Paradox of Its Tubular Eyes
Researchers solve mystery of deep-sea fish with tubular eyes and transparent head
Scientists Solve The Mystery Of Why This Fish Is So Freakin’ Crazy

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More Strange Animals To Come
I will be posting one new strange animal each and every day so if you enjoyed this post make sure to follow me and let's discover together some of the world's most strange and bizarre creatures! An upvote and resteem would be nice too :P In the meantime, you may want to check out some other weird animals I have posted about, like the lizard that shoots blood from its eyes, the pokemon-like Mexican Mole Lizard and this Giraffe like weevil!