They can be as big as great white sharks, but that’s about as far as the comparison goes.
Their maximum speed is a lethargic 1.7 miles per hour, many are almost blind, and they are happy to eat rotting carcasses.
They may be common throughout the ocean, but you’ve probably never heard of them. Meet the Greenland shark.
Looking like nothing so much as a chunk of weather-beaten rock, Greenland sharks (Somniosus microcephalus) can grow up to 7.3 metres (24 feet) long, making them one of the largest of all fish, and the biggest in the Arctic.
But they prefer to live in deep, cold water, so humans rarely see them.
Studies in the Arctic have revealed a few snippets of information about Greenland sharks, and more data is now starting to come in from elsewhere.
It turns out that Greenland sharks are bizarre, and may be crucially important for the ocean ecosystem.
Greenland sharks only come close to the surface in places where the shallow water is frigid enough for them – primarily in the Arctic.