Frilled shark. Image credit: Getty
Frilled shark. Image credit: Getty

6 Bizarre Sharks That Live in the Deep Ocean

Frilled shark. Image credit: Getty
Frilled shark. Image credit: Getty

Whether or not they deserve their notorious reputation, sharks are a common source of fear. But beachgoers shouldn’t worry about coming face-to-face with these spooky specimens—they all live at least 1000 feet below the ocean’s surface. From ghost sharks to goblin sharks, we’re here to shed light on the mysterious lives of these deep sea dwellers.

1. GREENLAND SHARK

The first part of the Greenland shark’s scientific name, Somniosus microcephalus, means “sleep,” a nod to its sluggish lifestyle. The second largest predatory shark in the ocean moves at a glacial pace of one mile per hour. The drowsy name also makes sense in the context of the effect the shark has on those who eat it. Its flesh contains the toxic substance trimethylamine oxide, and ingesting it can cause vomiting, diarrhea, convulsions, and the appearance of drunkenness (that’s why native Greenlanders call someone who’s had too much to drink “shark-sick”). The sharks are also capable of having abnormally long lives. In 2016, researchers found a specimen that had been cruising deep beneath the Arctic for the past 392 years.

2. GOBLIN SHARK

The goblin shark isn’t known for its dazzling good looks. Its defining feature is a jagged mouth of teeth that becomes even more pronounced when it launches forward from the skull to seize prey. Fortunately for anyone disturbed by its appearance, the goblin shark occupies depths up to 4265 feet where looks aren’t a priority.

A much bigger item on the species’s evolutionary agenda is finding sustenance. Food is hard to come by that far below the surface, so the species adapted by developing a relatively large mouth for trapping squid, fish, and crustaceans that pass by. They’ve long been known to Japanese fishermen (who originally named it tengu-zame after a long-nosed goblin from folktales), but much about these sharks still remains mysterious to scientists.

3. DEMON CATSHARK

Daniel Moore via Wikimedia Commons // CC BY 3.0

There are at least 32 species of demon catshark including the white ghost catshark, the smalleye catshark, and the Iceland catshark (above), but scientists still know little about their lives at the bottom of the Northeast Atlantic. The slow-moving creatures grow up to 2 feet long and feed on squid and crustaceans as far as 7000 feet beneath the sea. Their flat heads and gleaming, slanted eyes earned them their demonic name. Another distinctive feature of the Apristurus genus are the two spineless dorsal fins poking up from the back of the body [PDF].

4. SWELL SHARK

Not much light reaches the water 1640 feet beneath the ocean’s surface, but swell sharks have developed a unique way to catch each other’s eyes. Their skin absorbs what little blue light there is at the bottom of the sea and transforms it into brilliant green biofluorescent light. Swell sharks have a photoreceptor in their eyes that lets them detect the glow, whereas humans cannot.

A couple of years ago, a team of researchers found their way around this by building a camera with a blue light-blocking yellow filter. This allowed them to explore underwater environments with “shark vision.” Scientists aren’t entirely sure what function the biofluorescence serves, but they suspect it’s used as a form of communication between sharks. Swell sharks have a different super power for dealing with enemies: When threatened, they suck in large gulps of water, swelling up to twice their size (hence the name).

5. COOKIE CUTTER SHARK

Jennifer Strotman via Wikimedia Commons // Public Domain

This shark got its cutesy name from a rather gruesome behavior: When feeding, the 16- to 22-inch predators latch onto prey with suction cup lips and rotate to carve out medallions of meat. The wounds they leave behind are more scoop-like than cookie-shaped, and are inflicted on larger animals like marlin, tuna, wahoo, dolphins, and whales. They can be found 3200 feet deep during the day, but they wander upward at night to hunt, which has led to at least one attack on a human swimmer. Though a run-in with a cookie cutter likely wouldn’t be deadly, their creepy, tooth-filled “smile” isn’t something you'd want to see on a midnight swim.

6. FRILLED SHARK

Frilled sharks have been around for 80 million years, a fact that’s easier to process once you take a look at them. At the end of their prehistoric bodies is a mouth full of 300 teeth across 25 rows that glisten white to lure in prey.

The shark is named for its six pairs of gills which are each trimmed with red “frills.” In 2007, a group of fishermen made history when they spotted a live frilled shark in shallow waters off the coast of Japan. The fish was taken to the Awashima Marine Park in Shizuoka where it was transferred to a seawater pool. After some incredibly rare photographs were taken, the shark sadly died a few hour later.

BONUS: GHOST SHARK

In 2009, scientists with the Monterey Bay Aquarium Research Institute recorded video of a strange creature 6700 feet deep into the Gulf of California. It had a long nose, ghoulish gray skin, and saucer-like eyes that stared blankly into the surrounding abyss. Seven years later, a team of experts identified the creature to be a pointy-nosed blue chimaera, a species of ghost shark never before caught live on tape.

Despite its name, the ghost shark isn’t technically a shark. Chimaeras are close relatives that also use flexible cartilage in place of solid bone. Little is known about the group, but researchers suspect the lines of dots dimpling their snouts are used to detect prey. Males are also notable for wielding retractable sex organs on their foreheads.

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How Does Catnip Work?
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If you have a cat, you probably keep a supply of catnip at home. Many cats are irresistibly drawn to the herb, and respond excitedly to its scent, rubbing against it, rolling around on the floor, and otherwise going nuts. There are few things that can get felines quite as riled up as a whiff of catnip—not even the most delicious treats. But why does catnip, as opposed to any other plant, have such a profound effect on our feline friends?

Catnip, or Nepeta cataria, is a member of the mint family. It contains a compound called nepetalactone, which is what causes the characteristic catnip reaction. Contrary to what you might expect, the reaction isn’t pheromone related—even though pheromones are the smelly chemicals we usually associate with a change in behavior. While pheromones bind to a set of specialized receptors in what’s known as a vomeronasal organ, located in the roof of a cat's mouth (which is why they sometimes open their mouths to detect pheromones), nepetalactone binds to olfactory receptors at the olfactory epithelium, or the tissue that lines the mucus membranes inside a cat’s nose and is linked to smell.

Scientists know the basics of the chemical structure of nepetalactone, but how it causes excitement in cats is less clear. “We don’t know the full mechanisms of how the binding of these compounds to the receptors in the nose ultimately changes their behavior,” as Bruce Kornreich, associate director of the Cornell Feline Health Center, tells Mental Floss. Sadly, sticking a bunch of cats in an MRI machine with catnip and analyzing their brain activity isn’t really feasible, either from a practical or a financial standpoint, so it’s hard to determine which parts of a cat’s brain are reacting to the chemical as they frolic and play.

Though it may look like they’re getting high, catnip doesn’t appear to be harmful or addictive to cats. The euphoric period only lasts for a short time before cats become temporarily immune to its charms, meaning that it’s hard for them to overdo it.

“Cats do seem to limit themselves," Michael Topper, president of the American Veterinary Medical Association, tells Mental Floss. "Their stimulation lasts for about 10 minutes, then it sort of goes away.” While you may not want to turn your house into a greenhouse for catnip and let your feline friend run loose, it’s a useful way to keep indoor cats—whose environment isn’t always the most thrilling—stimulated and happy. (If you need proof of just how much cats love this herb, we suggest checking out Cats on Catnip, a new book of photography from professional cat photographer Andrew Martilla featuring dozens of images of cats playing around with catnip.)

That said, not all cats respond to catnip. According to Topper, an estimated 70 percent of cats react to catnip, and it appears to have a genetic basis. Topper compares it to the genetic variation that causes some individuals to smell asparagus pee while others don’t. Even if a cat will eventually love the smell of catnip, it doesn’t come out of the womb yearning for a sniff. Young kittens don’t show any behavioral response to it, and may not develop one until several months after birth [PDF].

But some researchers contend that more cats may respond to catnip than we actually realize. In one 2017 study, a group of researchers in Mexico examined how cats might subtly respond to catnip in ways that aren’t always as obvious as rolling around on the floor with their tongue hanging out. It found that 80 percent of cats responded to catnip in a passive way, showing decreased motor activity and sitting the “sphinx” position, an indicator of a relaxed state.

There are also other plants that have similar effects on cats, some of which may appeal to a wider variety of felines than regular old catnip. In a 2017 study in the journal BMC Veterinary Research, researchers tested feline responses to not just catnip, but several other plants containing compounds similar in structure to nepetalactone, like valerian root, Tatarian honeysuckle, and silver vine. They found that 94 percent of cats responded to at least one of the plants, if not more than one. The majority of the cats that didn’t respond to catnip itself did respond to silver vine, suggesting that plant might be a potential alternative for cats that seem immune to catnip’s charms.

Despite the name, domestic cats aren’t the only species that love catnip. Many other feline species enjoy it, too, including lions and jaguars, though tigers are largely indifferent to it. The scent of the plant also attracts butterflies. (However, no matter what you’ve heard, humans can’t get high off it. When made into a tea, though, it reportedly has mild sedative effects.)

The reason Nepeta cataria releases nepetalactone doesn’t necessarily have to do with giving your cat a buzz. The fact that it gives cats that little charge of euphoria may be purely coincidental. The chemical is an insect repellant that the plant emits as a defense mechanism against pests like aphids. According to the American Chemical Society, nepetalactone attracts wasps and other insect predators that eat aphids, calling in protective reinforcements when the plant is in aphid-related distress. That it brings all the cats to the yard is just a side effect.

Because of this, catnip may have even more uses in the future beyond sending cats into a delighted frenzy. Rutgers University has spent more than a decade breeding a more potent version of catnip, called CR9, which produces more nepetalactone. It’s not just a matter of selling better cat toys; since catnip releases the compound to ward off insects, it’s also a great mosquito repellant, one that scientists hope can one day be adapted for human use. In that case, you might be as excited about catnip as your cat is.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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12 Furry Facts About Red Pandas
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Red pandas have always lived in the shadow of the other, more famous panda. But now it's time to give the little guy its due.

1. THEY HAVE TWO EXTINCT RELATIVES.

Red panda in a tree.
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Currently, red pandas live in the Eastern Himalayas. But the first red panda fossil was found a little bit further afield than that—in the United Kingdom. In 1888, a fossil molar and lower jaw of a cougar-sized animal called the Giant Panda (unrelated to the modern giant panda) were discovered. More fossils have been found in Spain, Eastern Europe, and even the United States. Around 5 million years ago, Tennessee was home to a giant red panda that probably went extinct with the arrival of raccoons.

2. THEY'RE VEGETARIAN CARNIVORES.

Red panda eating bamboo.
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It might seem like an oxymoron, but carnivore in this case doesn't mean meat eater. Carnivore is a biological order that includes groups like bears, dogs, and cats, and while these animals are generally carnivores, some are omnivores, and some are vegetarians. Red pandas are classified as carnivores because they're descended from the same ancestors as the other carnivores, but they rarely eat anything other than bamboo and a few insects. And while giant pandas eat all of a bamboo plant, red pandas eat only the young leaves. Because this is such a nutritionally poor food source, they need to spend 13 hours a day eating and looking for food and can lose upwards of 15 percent of their body weight in winter.

3. THEY'RE SLIGHTLY BIGGER THAN A DOMESTIC CAT.

Red panda sleeping on a branch.
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But their tails add as much as 18 inches to their length. Red pandas live solitary lives in trees, high up in the mountains, so they wrap those big, bushy tails around themselves to keep warm. (They also use them for balance.)

4. THEY HAVE A FALSE THUMB.

Red panda perched on a log.
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This is another feature (along with diet) that red pandas and giant pandas share. Because both pandas have false thumbs—which is actually an extended wrist bone—it was thought that it must be an adaption to eating bamboo. But the red panda's more carnivorous ancestors had this feature as well. According to a 2006 study, what happened was "one of the most dramatic cases of convergence among vertebrates." Convergent evolution is when two unrelated animals faced with similar circumstances evolve to look similar. In this case, the red panda's false thumb evolved to help it climb trees, and only later became adapted for the bamboo diet, while giant pandas evolved this virtually identical feature because of their bamboo diet.

5. THEY'RE ESCAPE ARTISTS.

Red panda climbing across a tree.
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Rusty the red panda had been at the Smithsonian National Zoo for just three weeks when he made a break for it in June 2013. His method of escape? A tree branch that was pushed down over his enclosure's electric fence by heavy rains. The ensuing panda hunt (and endless bad jokes about panda-monium) captivated Twitter (tweeters used the hashtag #findrusty) until he was found in a nearby neighborhood. Soon after his daring escape, Rusty became a father, forcing him to put his wild youth behind him and settle down. But it could have been worse. After a similar escape in Dresden, Germany, the authorities got another red panda down from a tree by using a fire hose to spray it with water. The panda fell 30 feet to the ground, giving it a concussion. (Ultimately, the animal was OK.)

Red pandas have also escaped from zoos in London, Birmingham, and Rotterdam. The Association of Zoos and Aquariums even warn in their official care manual "beware: red pandas are escape artists" [PDF].

6. ONE ESCAPE LED TO SOMETHING CALLED THE RED PANDA EFFECT.

Red panda peeking out from behind some tree branches.
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Sadly, the red panda involved in the 1978 Rotterdam escape was found dead not long after the search for it began. But the event led to a very peculiar psychological observation. Even after the body of the panda was found, more than 100 people reported seeing it, very much alive. These sightings were clearly mistaken; there's no reason to think that multiple red pandas were loose in Rotterdam, and red pandas are distinctive enough that mistaking them for a dog or cat was unlikely. It's believed that people expected to see a red panda, so they saw one, even though there wasn't one there; researchers called it the Red Panda Effect.

7. THERE'S AN INTERNET BROWSER NAMED AFTER THEM.

The Mozilla Firefox logo.
LEON NEAL, AFP/Getty Images

Mozilla's flagship browser, Firefox, means red panda. Originally, Mozilla wanted to name the browser Firebird, but found that another open source project was using that name. Not wanting to upset anyone, they decided to go with Firefox, another name for the red panda. And in a true example of adorableness, in 2010 Mozilla adopted two baby red pandas that had been born at Tennessee's Knoxville Zoo.

8. THERE IS ONLY ONE TRUE PANDA—AND YOU CAN PROBABLY GUESS WHICH ONE IT IS.

Engraving of a parti-colored bear.
Engraving of a parti-colored bear, from The New Natural History Volume II by Richard Lydekker, 1901.

After the red panda was discovered in the 1820s, it was just called the panda (the origin of the name is controversial, but it probably comes from the Nepali word ponya, meaning "bamboo or plant eating animal"). Forty years later, Europeans found a new animal in China and called it the Parti-Colored bear—because unlike polar bears, black bears, or brown bears it was multi-colored.

9. THERE HAS BEEN A 140-YEAR TAXONOMIC MIX-UP.

A red panda walking toward the camera.
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Prepare to be confused: In the late 19th century, scientists noticed that the parti-colored bear and the (red) panda were very similar. Their jaws were more like each other than they were like any other animal, they lived near each other, they both had false thumbs, and their diets were similar. The decision was made to officially consider the (red) panda as a type of bear.

By the early 20th century, that decision was reversed: Parti-colored bears were declared bears, and (red) pandas were classified as cousins of the raccoon.

Then, in the 1910s, it was decided that parti-colored bears weren't actually bears at all, but were actually large pandas, and also distant relatives of the raccoon. But because parti-colored bears weren't classed as bears anymore, they had to have a name change. They became giant pandas, while the one true panda was renamed the red or lesser panda (to quote a 1920 issue of Popular Science: "Zoologists reverently refer to this rare beast as the "giant panda." Its more popular cognomen is the 'bear-raccoon'").

10. BUT RED PANDAS ARE THEIR OWN THING.

Two red pandas touch noses.
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By the 1980s, genetic evidence indicated that giant pandas actually were a type of bear, and red pandas belonged in their own family, the Ailuridae. They might seem similar, but they're not related.

All of this means that if you're the type of person who rolls their eyes when someone calls a bison a buffalo, or a koala a bear, you need to stop calling the bear a panda and instead refer to it as a "parti-colored bear," the original English name (but if you wanted to call it the bear-raccoon, no one would stop you). Giant pandas are not pandas. There is only one true panda.

11. BUT THIS DOESN'T AFFECT KUNG FU PANDA 3.

Red panda with teeth bared.
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There's still a kung fu panda in the series: Shifu, a red panda.

12. THEY'RE ENDANGERED.

Red panda laying down and sticking his tongue out.
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According to the World Wildlife Fund, there are fewer than 10,000 red pandas left in the wild. Habitat destruction increases the species' chances of extinction.

This story originally ran in 2015.

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