Greenland shark

The Greenland shark (Somniosus microcephalus), also known as the gurry shark, grey shark, or by the Kalaallisut name eqalussuaq, is a large shark of the family Somniosidae ("sleeper sharks"), closely related to the Pacific and southern sleeper sharks. The Greenland shark is a potentially important yet poorly studied cold-water species inhabiting the North Atlantic and Arctic Oceans. The Greenland shark has the longest known lifespan of all vertebrate species (estimated to be between 250 and 500 years), and is among the largest extant species of shark. It is a generalist feeder, consuming a variety of available foods. As an adaptation to living at depth, it has a high concentration of trimethylamine N-oxide in its tissues, which causes the meat to be toxic. Greenland shark flesh, treated to reduce toxin levels, is eaten in Iceland as a delicacy known as kæstur hákarl. As it lives in the cold depths of the Arctic and North Atlantic, isolated from human activity, it is not known to be a threat to humans, and no attacks have been recorded. The Greenland shark is likely one of the largest living species of shark. It usually grows to between long and weighs between . Males are typically smaller than females. It rivals the Pacific sleeper shark (possibly up to long) as the largest species in the family Somniosidae. The Greenland shark is a thickset species, with a short, rounded snout, small eyes, and very small dorsal and pectoral fins. The gill openings are very small for the species' great size. Coloration can range from pale creamy-gray to blackish-brown and the body is typically uniform in color, though whitish spots or faint dark streaks are occasionally seen on the back. When feeding on large carcasses, the shark employs a rolling motion of its jaw. The 48 to 52 teeth of the upper jaw are very thin and pointed, lacking serrations. These upper jaw teeth act as an anchor while the lower jaw proceeds to cut massive chunks out of the prey. The 48 to 52 lower teeth are interlocking, broad and square in shape, containing short, smooth cusps that point outward.