I need answers.

Self promoting this video and sending it back into the queue for one more try; last queued Sunday, May 3rd, 2015 5:01pm PDT - promote requested by original submitter eric3579.

Looks like it discharged its cuvierian tubules.
https://en.wikipedia.org/wiki/Cuvierian_tubules

It looks like it's inspiring anime.

@eric3579, why not link directly to youtube?

Cos the video repeats itself three times which kinda annoys me. Is there a disadvantage to tube chop that i'm not aware of? I have no problem changing it if someone would rather it be a yt embed.

-edit-
Changed

For some reason it's completely blank for me in Firefox and Chrome. Only works in IE.

I know exactly what kind of worm that is: it's a put-it-the-fuck-down worm. You can identify them by the way your girlfriend screams, "AHHHHH!! PUT IT THE FUCK DOWN!" as soon as it does its little trick.

I am giddy that I get to inform everyone here that the explosive defensive organ seen in this video does not come out of the creatures mouth.

....

I think you know what I'm saying.

...hmmm...looks vaguely familiar.

http://videosift.com/video/Monster-leech-swallows-giant-worm ?

TETSUO!

That's what i though of immediately. Well that scene in the movie.

Are you saying it's a butt-shooting worm?

...Well, technically I suppose it's more of a cloaca-shooting worm.

But yeah. Pretty much.

And it is definitely a sea cucumber species of some kind. I've seen then while snorkeling, and my dad picks them up on dives and intentionally tries to get them to do this. I've seen him do it, and I feel like I've seen them gradually start to suck the guts that get expelled back into their bodies. If they really can't do that, as @atara 's link suggests (but they regenerate in roughly a month or less I guess) I might discourage him from provoking them to do that intentionally in the future.

It's drunk.

UPDATE below also see new video description and original video

The caption is in Thai and describes the creature as a Nemertea, or a ribbon worm, which shoots a proboscis (elongated nose) out of a hole above its mouth to capture prey.

Presumably, that is what is going on here.

When not stretched out like an alien life form, the proboscis normally sits in “a fluid-filled chamber above the gut,” according to Encyclopedia Britannica.

And here’s a description of how it works from NCSU:

"When the animal senses a prey organism nearby, a circular muscle layer around the proboscis sheath rapidly and vigorously contracts. This contraction forces the fluid from the proboscis sheath into the proboscis and, in the process, literally turns it inside out, blowing it out of the proboscis sheath. The proboscis will rapidly (within a second or so) wrap itself around the prey, which is then drawn to the mouth and eaten."

from http://thedailywh.at/2015/05/nope-day-internet-disgusted-mystified-ribbon-worm/

Looks like it's creating a duplicate.

"Cue Donald Sutherland."

I don't think the original video had audio, or at least I didn't hear it. Fun to hear them talking about it in Thai, although they don't say anything particularly scientifically relevant -- more like "augh! help me!" (out of surprise) and then some mild cussing about it.

The caption/title I get from the original video says:
"น่ากลัว หนอนทะเล เป็นแบบนี้"

First word is "na-grua" which means "scary", or more directly/literally "worthy of fear". The second word is compound, "nohn-talay" which means "worm-ocean", or "marine worm" would be a less literal but better English translation. The last word is actually 3 words: "pben baap ni", which roughly means "is like this". So an overall translation of the YT video title would be "this is a scary marine worm".

...Oops, and just now I'm seeing the YT description, which has a lot more Thai and does specifically mention Nemertea -- so that is probably correct. It looks and behaves a lot like some of the sea cucumbers that I've seen, although most tend to have a bit more texture or protrusions on their skin. But there are definitely sea cucumbers that are as smooth as this thing. Compare with a similar sea cucumber video:

https://www.youtube.com/watch?v=lKWSLg5PDiU

Quite similar, but sounds like the Nemertea does this to eat whereas the Sea Cucumber does it as a defense mechanism.
--EDIT-- Whoops, embedded the wrong video. Should be fixed now

*dead

This video has been declared non-functional; embed code must be fixed within 2 days or it will be sent to the dead pool - declared dead by oritteropo.

Taiwanese fishman catches a ribbon worm has been added as a related post - related requested by blackfox42 on that post.