Imagine you're a shark (let's go with a kitefin shark).
One day, you find yourself swimming around, looking for some dinner. Finely tuned senses lead you down to the ocean floor, where the carcass of an old whale lies ready and waiting.
But somebody beat you to the buffet. Out of the corner of your eye, you see the tail end of a wriggling, eel-shaped creature.
As you turn to get a closer look, you notice that this other animal, whatever it is, has buried its head in the dead meat. The corpse can wait. You decide to make a meal of this thing instead.
Then, just as you wrap your jaws around it, the scavenger lets loose a milky cloud of slime. Fibrous, suffocating slime. The gunk floods your mouth and gills, forcing a hasty retreat.
Congratulations, you've just had an encounter with one of the ocean's weirdest characters: a slime-producing hagfish.
What Is a Hagfish?
Long and snakelike, hagfish might bear a passing resemblance to eels.
Yet looks can be deceiving. The sinuous hagfish make up a totally different family of vertebrate animals, a group called the Myxinidae.
"There are exactly 87 described species of hagfish," says Salisbury University physiologist Noah Bressman, in an email. "However, there are likely more species out there yet to be described."
The family's lifestyle preferences make it tough to get an exact headcount. Members of the Myxinidae reside in every ocean; you can find them within the Arctic Circle, just above the Antarctic Circle and at plenty of locales in between.
Tropical or temperate waters are the ideal home for most hagfish. Potential habitats include coral reefs and hydrothermal vents.
"They are normally found on the seafloor in very deep water at the bottom of all oceans, sometimes over a mile [or 1.6 kilometers] down," says Bressman.
Being, in his words, "escape artists capable of getting out of the tiniest holes," the fish are not easily captured by researchers.
"Some species also burrow in the mud or sand, while others may hide out in rock crevices," Bressman explains. "Taken together, these factors make hagfish unlikely to be sampled with conventional fishing gear, so many species have likely gone unnoticed."
No Jaws? No Problem
A notable trait of the hagfish family is their lack of jaws.
To "bite" things, they use an appendage that's often compared to a tongue. It's lined with opposing rows of sharp, toothy rasps. When the not-quite-a-tongue is retracted into the creature's head, those rasps pinch together, ensnaring food.
If that's not strange enough for you, try this on for size. Scientists have discovered that when hagfish go scavenging and dig their way inside a tasty carcass, they can absorb some of the dead animal's nutrients directly through their gills and skin.
Hagfish are well equipped to eat the deceased. But that doesn't make them obligatory scavengers, per se. One 2011 study reported that at least some species proactively hunt down other fish.
Like Dr. Zoidberg says, a feast is a feast.
Marine bio enthusiasts might also be interested to learn that hagfish are limited to one nostril apiece. Their loose-hanging skin works as a defense mechanism because it's hard for attackers to penetrate. And like sharks, hagfish have skeletons that are largely cartilage-based.
Skein In the Game
Hagfish have one more quality we ought to mention.
If they're attacked, or just stressed out, the bottom-feeders respond by discharging a chemically unique slime. The brew can be fatal to certain types of marine life.
"There are two major components to hagfish slime," Bressman says. "The first is mucous vesicles, which rupture and expand rapidly when exposed to seawater."
Protein threads are the other big ingredient. Each strand of this silk-like material is about 5.9 inches, or 15 centimeters, long. They're kept in tight little bundles wound up inside special cells known as skeins.
Once the skeins make contact with seawater, Bressman tells us they "rapidly unravel ... forming a matrix with the mucus to create the hagfish's signature slime."
A network of pores and glands have evolved to discharge this stuff at just the right moment.
"Hagfish [secrete] their slime as a defense against gill-breathing predators, like sharks," explains Bressman. "When a [predator] bites down on a hagfish, the hagfish contracts muscles surrounding their slime glands, causing them to secrete their slime exudate into the water. This concentration then rapidly expands into the fish's mouth, attaching to the gill arches. With the gills clogged, the fish may choke and suffocate from the slime, causing them to release the hagfish."
Marine biologists have seen it all before. In 2011, the journal Nature published a study on hagfish behavior. The paper's authors had left "bait bags" on the ocean floor near New Zealand. Various sea critters were then filmed as they investigated the free meal.
On 14 separate occasions, the team got footage of a bigger fish — like the kitefin shark — trying to gobble up a scavenging hagfish:
You can see how that went over.
"The hagfish, in all cases, appeared to sustain no injury, often continuing to feed on the bait, while the predator moved away, gagging," wrote the authors.
Move Over, Nylon?
Oregon motorists had a run-in with this particular brand of ooze a few years ago.
Hagfish are a popular food in Korea; diners can get them cooked or broiled and they're frequently paired with a red pepper sauce.
Well, in 2017, a truck loaded with Korea-bound hagfish made the news. Its driver had to suddenly brake while trekking across U.S. Highway 101 in Oregon.
Dislodged by the stop, a container full of hagfish fell off the truck and collided with another vehicle. White goop smeared the roadway in a multi-car pileup as the animals wriggled free.
Restaurateurs are not alone in their enthusiasm for hagfish. The oddballs have become minor celebrities in the world of fiber technology. Experts say the ultra-tough protein threads in hagfish slime could someday inspire a plastic-free alternative to polyester and nylon.
"While much is still to be learned about hagfish slime threads before they (or manufactured threads based off slime threads) are widely used," says Bressman, "their qualities have garnered the attention of textile companies, the military and many other interested parties."