Now this is my favourite fish. It's actually 510 million years old. Now to put that in perspective, the straggliest, most unimpressive plant only came ashore 425 million years ago, and that rabbitfish we saw, fossils almost identical to it that's only 300 million years ago, and the rabbitfish now is a living missing link, as far as you can have such a thing, because it's a real intermediate between the fishes that are... the teleos and the bony structure, and those on a... that are made from cartilage, like the rays and the sharks. So this is, as it were, almost old beyond belief. And very impressive. Impossible to kill. These things would come up from a mile down, a bit fazed by being in the net, presumably, but here he is, already sniffing out a new home. Now when you're drowned, they love liver, hagfish, and I'm afraid the quickest way in... they always enter via the anus. Not their fault. Not your fault. And make their way to the liver as fast as they can, with these rasping, rasping, no, not teeth... they evolved way before teeth evolved. Their opposable horny plates, like this.

And actually incredibly sharp and they make their way up the gut and they swarm, so there's one after the other, so there's a panic for them to get to your liver. And I'll show you in detail in a minute, but the reason all trawler men detest them is because if you are unlucky enough to get a body in your trawl, say, a drowned trawler man, or in the case I'm thinking of, 45... I think probably they were SAS men, anyway, helicopter crash during the troubles off the Mull of Kintyre. And the Norlantean sister ship, in her trawl, 30 corpses.

[Q] In the net?

In the net, yes. Come up into the hopper. Luckily somebody got to the hopper first, otherwise not a single man in that crew would ever have gone to sea again. And they were in their uniforms, but distended and absolutely flapping with these things. They were just full of hagfish. So there's a nasty story for you, but this... it is a most remarkable animal, and, I think, terribly sophisticated, given the fact that it's so old. You know, what was it preying on, as it certainly was? I don't... you probably can't see, but there are about 500 little white glands, as it were, that you can see along the dorsal, the ventral, fins, such as it is. It is like a hedge. Now some of them are full of a substance that is fascinating. It hydrates faster than anything else known on Earth. Powder, white powder, boom, and it fills with the surrounding water, and makes a gooey, slimy, filthy substance. And some of those cells have got little tiny threads in them. They also expand. And the threads and the goo mesh together. And again, if you're a shark who really should've stayed on at school a little longer, and you see one of these, this is a frankfurter for breakfast. As you come in, it picks you up with these massive receptors here, and almost instantaneously, 500 glands open, boom.

And it's surrounded in a great ball of slime. And it's in your gills, it's in your eyes, it's in your mouth. And you do what you'd think you'd do: you shake your head. And the more you do that, the tighter it sets. It's nightmare stuff. And Jason said he'd quite often seen big Greenland sharks, okay? Slow-moving bottom eaters, dead on the surface, strangled with this slime set around their huge heads. Don't mess with this little frankfurter. Astonishing. How you evolve a defence like that. One theory is that actually they do it... they put out a lot of slime the minute they find something dead on the sea floor. I mean, it can be a dolphin, it can be a fish, it can be you or me. And that keeps the other... the competition off. Not your fellows, you know, they don't mind the slime, but other nasty... all the amphipods, all those... you know, the lesser beings. It keeps them off. And then you say, well, that's all very well, but they're going to strangle themselves in their own slime. Well no, this is the only animal, as far as we know, on Earth, that can tie a knot in itself. Puts its head around in a knot and then passes the know down its body, see? Never needs to take a shower.