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Living in arctic conditions affects the Greenland shark in a number of remarkable ways. For one, they move incredibly slow, at an average speed of fewer than one mile per hour. But their movement isn't the only thing slow about them; they also grow slowly. Adult Greenland sharks may reach up to 16 feet, but will only grow about one centimeter each year. At that rate, it takes about 150 years for a female Greenland shark to reach maturity. With such a slow growth rate, it's only natural that these sharks would have exceptional longevity, often living up to 400 years.

Greenland sharks are unique for many reasons, one of which is that they are the only species of shark that can survive in Arctic temperatures, according to Fisheries and Oceans Canada. These sharks mostly live in polar regions in the North Atlantic Ocean but have also been sighted at extreme depths of lower latitude oceans.

The frilled shark is the stuff of nightmares, and not just because it looks like a beady-eyed eel. This deep-dwelling species of shark also has 25 rows of razor-sharp teeth. Their 300 triangular teeth are good for locking down on their slippery prey⁠—cephalopods, including octopus, cuttlefish, and squid. Because these sharks belong to a primitive species that has hardly evolved over millions of years, they're sometimes referred to as "living fossils."

Sharks are growing new teeth all the time, too. In fact, many sharks are able to replace a lost tooth in a matter of days or months. As long as the shark stays healthy, it will continue to be able to grow unlimited new teeth for the rest of its life.

Unlike human teeth, shark teeth don't have roots, making them liable to fall out. Considering that some species may have as many as 300 teeth in their mouth at a time, that's quite a lot of tooth loss. In fact, some sharks may only have a tooth for about a week before losing it.

Imagine eating whatever you wanted and never getting a cavity. That's the reality for makos and tiger sharks, whose teeth are naturally coated in fluoride, according to 2012 research published in the Journal of Structural Biology. All the better for maintaining strong, healthy teeth that can bite into all kinds of flesh.

Sharks have been on this planet for hundreds of millions of years, yet fossils show little record of their existence. That's because they're elasmobranches, or species that have cartilage instead of bones, meaning most shark carcasses decompose before a fossil has time to form. Other elasmobranches include rays, skates, and sawfish. The only bones you'll find in a shark's body are its teeth, which it has plenty of!

These deep-sea creatures, also called chimera and ratfish, are mysterious, and not just because they lurk in the depths of the ocean. Among their most curious features is the male ghost shark's s*x organ, which protrudes from its head and attaches to the female's pelvis during copulation, according to National Geographic. Female ghost sharks can hold onto this s***m and use it when they desire, sometimes up to three years later

Blue light doesn't only come from screens. Nearly 1,700 feet beneath the ocean's surface, you'll find the swell shark to be another unlikely source of it. For reasons still unclear to scientists, these sharks emit a fluorescent glow that's only visible to other swell sharks. Scientists themselves have only been able to detect the glow using filters that block out yellow light. According to biologist David Gruber of the City University of New York, these creatures glow so they can communicate with their other swell shark pals.

Blood in the water may be the most obvious signal that shark bait is lurking, but did you know that sharks also respond to sound? Sharks are able to pick up on super low frequencies that are undetectable to the human ear. For example, when dying fish give off low-pitched infrasound, sharks hear it and head off to finish the job. This low-frequency buzz, often referred to as a "yummy hum," is a useful hunting tool for predatory sharks, according to the Discovery Channel.

“New car smell” is composed of 50 volatile organic compounds (VOC). Prolonged exposure to VOCs can result in serious health effects. Mmm, I love the smell of 50 volatile organic compounds in the morning!