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.
Mas alguém chegou antes de você no bufê. Com o canto do olho, você vê o rabo de uma criatura em forma de enguia se contorcendo.
Ao se virar para olhar mais de perto, você percebe que esse outro animal, seja lá o que for, enterrou a cabeça na carne morta. O cadáver pode esperar. Você decide fazer uma refeição dessa coisa em vez disso.
Então, assim que você envolve suas mandíbulas em torno dele, o necrófago solta uma nuvem leitosa de lodo. Lodo fibroso e sufocante . A gosma inunda sua boca e guelras, forçando uma retirada apressada .
Parabéns, você acabou de encontrar um dos personagens mais estranhos do oceano: um peixe-bruxa produtor de lodo.
O que é um peixe-bruxa?
Longo e parecido com uma cobra, o peixe-bruxa pode ter uma semelhança passageira com as enguias.
No entanto, as aparências podem enganar. Os peixes-bruxas sinuosos compõem uma família totalmente diferente de animais vertebrados, um grupo chamado Myxinidae .
“Existem exatamente 87 espécies descritas de peixes-bruxa”, diz o fisiologista da Universidade de Salisbury, Noah Bressman, em um e-mail. “No entanto, provavelmente há mais espécies por aí ainda a serem descritas”.
As preferências de estilo de vida da família tornam difícil obter um número exato de funcionários. Os membros dos Myxinidae residem em todos os oceanos; você pode encontrá-los dentro do Círculo Polar Ártico , logo acima do Círculo Antártico e em muitos locais entre eles.
Águas tropicais ou temperadas são o lar ideal para a maioria dos peixes-bruxa. Os habitats potenciais incluem recifes de coral e fontes hidrotermais .
“Eles são normalmente encontrados no fundo do mar em águas muito profundas no fundo de todos os oceanos, às vezes a mais de uma milha [ou 1,6 km]”, diz Bressman.
Sendo, em suas palavras, "artistas da fuga capazes de sair dos menores buracos", os peixes não são facilmente capturados pelos pesquisadores.
“Algumas espécies também se enterram na lama ou na areia, enquanto outras podem se esconder nas fendas das rochas”, explica Bressman. “Juntos, esses fatores tornam improvável que o peixe-bruxa seja amostrado com artes de pesca convencionais, então muitas espécies provavelmente passaram despercebidas”.
Sem Mandíbulas? Sem problemas
Uma característica notável da família dos peixes-bruxa é a falta de mandíbulas .
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.
Getting Slimed
"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."
Now That's Interesting
Like sea snakes , hagfish have been known to tie themselves into knots. The maneuver helps these fish rip meat off carcasses by providing them with leverage.
