But for everything the hagfish lacks, it makes up for with incredible amounts of weird and unusual slime, which it uses to protect itself against predators.
Based on their simple features, scientists long thought hagfish were primitive, but struggled to figure out where they fit on the evolutionary timeline for other fish and backboned vertebrates. Ed Yong, a staff writer for The Atlantic, says the evolutionary relationships between hagfish and other fish have been controversial for a long time.
"A lot of scientists have thought of them as very primitive creatures, like some sort of transition from a kind of worm-like thing to a fish-like thing, like a precursor to backboned animals like us," Yong told NPR's Scott Simon.
Part of the problem was that until relatively recently, the hagfish had virtually no fossil record to offer clues. But in a study published this month in the Proceedings of the National Academy of Sciences, a fossil called Tethymyxine offers some new insight. Acquired by the Black Hills Institute of Geological Research in 2013, the fossil is described in the study as "an unequivocal fossil hagfish."
The fossil, discovered in a Lebanese quarry, measures 12 inches in length and includes remnants of preserved slime dating to 100 million years ago. The chemicals in the preserved slime glands match the composition of modern-day hagfish slime.
After studying the fossil, researchers concluded that hagfish are not primitive precursors to vertebrates, but hypothesized that the creatures are actual vertebrates themselves.
In his piece for The Atlantic, Yong explained the significance of that discovery:
If it's right, then hagfish aren't primitive evolutionary throwbacks at all. Instead, they represent a lineage of vertebrates that diverged from all the others about 550 million years ago, and lost several traits.
"They are part of the backbone lineage," Yong said in his interview. "They just seem to have lost a lot of the traits that we have — things like complex eyes and bones and taste buds. So rather than being this weird evolutionary throwback, they're actually quite specialized."
Their biggest specialization? Their slime, lots and lots of slime.
The slime is an evolutionary trait that the hagfish uses to protect itself. They release less than a teaspoon of slime from glands on its side when they're attacked or stressed. But in a fraction of a second, that teaspoonful expands into liters of slime.
"If you put a hagfish in a bucket at first it'll look like these thin wisps of this like white cloudy stuff have been released from its flanks," Yong said. "And then if you stick your hand and swirl it around, you would just be pulling out like handfuls of this stuff. It's almost like the entire bucket will have converted into slime."
The slime is perfect for infiltrating nooks and crannies, especially the mouths and gills of predators. When hagfish are attacked, they release a cloud of slime that effectively suffocates the attacker.
"Hagfish tend to scavenge dead and dying corpses at the bottom of the ocean. So those attract a lot of other things like sharks, so they often get bitten," Yong said. "There have been these incredible videos of sharks biting hagfish and then just recoiling their mouths and gills full of slime and just gagging and being forced to retreat."
The thought of a cloud of slime is enough to make anyone want to retreat, but after hearing from scientists about the slime, Yong said he would like to see what it feels like.
"It's not as revolting as it looks like or it might sound like," Yong said. "It's not sticky. You could actually wipe it off fairly easily and it feels almost, I'm not going to say pleasant, but kind of strange, like almost ethereal."
Though hagfish live a somewhat grim, grotesque life, feeding on corpses and sliming things that might want to eat them, the new discovery suggests there might be more than meets the eye with these creatures — or rather, the lack of eyes.
SCOTT SIMON, HOST:
You might want to set aside your cornflakes for a moment now. Ed Yong writes in The Atlantic about a substance he says, quote, "looks revolting but is also one of nature's more wondrous substances, unlike anything else that's been concocted by either evolution or engineers." Ed Yong, science writer for The Atlantic, joins us now. What are you celebrating here?
ED YONG: Hi. I am celebrating the slime produced by a type of fish called the hagfish. So the hagfish is, you know, a 2-foot long creature that lives in the deep ocean. It looks a bit like an eel, but it's not. It has no backbone. It has no jaws. And, most tellingly, it has the ability to produce incredible amounts of this very, very weird and unusual slime.
SIMON: I guess we could both make a lot of jokes about how similar it is to members of the U.S. Senate, but (laughter)...
YONG: Can neither confirm nor deny that.
SIMON: Slime. A teaspoon of slime at first, but it really multiplies, doesn't it?
YONG: So a hagfish will release about less than a teaspoonful of the slime from the glands on its side. But in, like, less than half a second, that teaspoonful will expand into liters of slime. If you put a hagfish in a bucket, at first, it'll look like these thin wisps of, like, white, cloudy stuff have been released from its flanks. And then, if you stick your hand in and swirl it around, you'll just be pulling out, like, handfuls of this stuff. It's almost like the entire bucket will have converted into slime.
SIMON: But this is what they do to protect themselves?
YONG: Right, it's a defensive measure. They release it when they're attacked or when they're stressed.
SIMON: Because a lot of predators might say, ha-ha-ha, no backbone, no teeth? I know what I'm having for lunch.
YONG: Right, exactly. They often get bitten and attacked. But when they do, they instantly release this massive cloud of slime which is very, very good at infiltrating nooks and crannies, including the mouths and gills of predators. So there have been these incredible videos of sharks biting hagfish and then just recoiling, their mouths and gills full of slime and just gagging and being forced to retreat.
SIMON: Sharks essentially saying, I'm sorry (laughter). I'm not a Spielberg shark. They don't pay me enough to swallow slime.
YONG: I think it's more like they're saying, (vocalizing).
SIMON: (Laughter) Now, hagfish slime is in the news because of a new fossil, right?
YONG: So partly, yes.
SIMON: A newly discovered fossil.
YONG: A newly discovered fossil. The fossil is interesting because the evolutionary relationships of hagfish to other fish have long been controversial. Like, a lot of scientists have thought of them as very primitive creatures, like some sort of transition from a kind of worm-like thing to a fish-like thing. But this new fossil helps us understand that it looks like hagfish are vertebrates. They are part of the backbone lineage. They just seem to have lost a lot of the traits that we have, things like complex eyes and bones and taste buds. So rather than being this weird, evolutionary throwback, they're actually very, very well-adapted animals to the somewhat grim and grotesque life that they live at the bottom of the ocean, feeding on corpses, sliming things that might want to eat them.
SIMON: Oh, boy, does that sound - ah, what a life that sounds like.
YONG: (Laughter) Right. But I tell you what, I was serious when I said that it's one of evolution's marvels. I think very rarely do you see a substance with this combination of properties produced by an animal that most people have never heard of.
SIMON: Ed Yong covers science for The Atlantic. Thanks so much for being with us.
YONG: Thanks for having me. Transcript provided by NPR, Copyright NPR.