Greenland shark

The Greenland shark (Somniosus microcephalus), also known as the gurry shark or grey shark, 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; it is among the largest extant species of shark. It reaches sexual maturity at about 150 years of age and pups are born alive after an estimated gestation period of 8–18 years. It is a generalist feeder, consuming a variety of available foods. As an adaptation to living at depth, it has 3 kinds of hemoglobin and a high concentration of trimethylamine N-oxide in its tissues to increase buoyancy. This causes the meat to be toxic to mammals. 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.