Deep below the surface of the ocean, there's an animal that goes by the name frilled shark.
But it doesn't look or act anything like its shark relatives.
The animals are sometimes referred to as "living fossils." That's because their fossils date back as many as 80 million years, and some scientists think they have relatives that could have lived more than 300 million years ago.
Their mostly unadapted form is more like an animal we think of from the prehistoric era than one that normally swims the seas today.
The rarity of frilled shark sightings adds to their mystery. The animal lives deep underwater, so humans don't see it often. The few fishermen who have seen it usually react in horror. It's not hard to see why.
At around 5 to 7 feet, it might appear to be the biggest eel fishermen have ever seen. But then it opens its mouth.
Inside its jaw, the frilled shark has several rows of needle-like teeth that extend across its long, flat jaw — enough of an oddity to give any fisherman who thought he caught an eel a bit of a fright.
We know very little about the frilled shark, so those teeth are the subject of a lot of speculation. Some scientists believe those small, jagged teeth — while not having the same bite power of other shark species — are the perfect size for snagging squid.
It could also be that the teeth, which appear bright against the darkness of the deep sea and the shark, might even serve as bait for the frilled shark's prey.
Once a meal is ensnared in the teeth, the frilled shark's flat jaw allows the animal to swallow it whole.
That quickness is key, since the frilled shark isn't known to be a super intelligent or vicious predator.
One Japanese fisherman did catch one in 2007. It was probably the best chance scientists had to learn a lot more about the animal. Sadly, though, it died shortly after being put in a seawater tank at a nearby aquarium.