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There are plenty of creatures out there with only one opening to handle the business of both taking in food and getting rid of the leftovers. Jellyfish, for example, get along fine with a mouth that's also an anus.

But there's at least one animal out there that doesn't have a gut opening…at all. The giant tube worm Riftia pachyptila lives over a kilometer deep in the ocean, along ocean ridges, where hydrothermal vents are common and spew boiling hot, chemical-laden water into the freezing cold deep sea. These chemicals include stuff like hydrogen sulfide, which isn't all that great for most animals.

But these bizarre-looking worms are adapted to live in this hostile habitat, without so much as a mouth to make things easier. Riftia almost look like a lipstick, with their vivid red plumes and tube-like outer casing. Within, they have a structure called a trophosome, which is like a gut, but with no way in or out.

They were first discovered in 1977 when the submarine ALVIN accidentally landed on a cluster of them while it was investigating hydrothermal vents near the Galapagos. Red blood gushed up around the sub. The researchers on board later discovered that the tube worm's plume has blood vessels full of hemoglobin.

In us mammals, hemoglobin is mainly responsible for transporting oxygen. In Riftia, the tube worm's plume acts like a gill. Its hemoglobin helps pull that hydrogen sulfide from the vent water and move it into the trophosome.

Inside the trophosome are millions of symbiotic bacteria, accounting for up to half the body weight of the worm. The bacteria are able to convert the toxic vent water chemicals into a food source for the worm, through a process called chemosynthesis. Much like plants use photosynthesis to produce food using sunlight, these bacteria are getting their food through chemical reactions that use hydrogen sulfide to produce energy.

And the inside of a worm is a much better habitat for them than the open vents -- or so the hypothesis goes. Not only have the bacteria turned this hostile environment into an advantage -- the worms have capitalized right along with them. They don't need a mouth or anus -- they just get fed by their bacterial partners, which produce enough food to keep everyone happy.

It's like having your kitchen inside your body! OK! So that's how the food gets in, but how does it get out? well the waste produced from digesting this food can be transported back out via the worms' bloodstream, there's no need for either a mouth or an anus.

But it begs the question: How do those personal chefs get there? Researchers asked this question in 2006 and found that it's… weird! The bacteria enter through the tube worm's skin when it's still a larva.

It's basically a bacterial infection. Hydrothermal vents are an unpredictable place to call home, thanks to the constant tectonic activity happening along ocean ridges. They may be there one day and gone the next.

Once the vents stop venting, the tube worms die because their bacteria's food source gets cut off. The distance between them can be several miles, which is a long swim when you're a little worm. So researchers aren't sure how tubeworm larvae get from place to place without a food source.

Hypotheses range from whale falls to shipwrecks -- which would supply enough of the chemicals the bacteria need to stay alive. The discovery of these weird worms and their unique way of eating has led to researchers finding chemosynthetic communities in ecosystems around the world -- from elsewhere in the ocean to Yellowstone National Park. Who knew a giant, mouthless, buttless worm could completely redefine the way we thought about how life works on our planet?

Thanks for watching, and thanks to our patrons for helping us bring this video to the world! What world would it be without it! If you want to help out and join our amazing community of supporters, check out patreon.com/scishow. {♫Outro♫}.