Claim: Cartilage comprises the skeleton of Greenland sharks.

The Greenland shark -LRB- Somniosus microcephalus -RRB- , also known as the gurry shark , or grey shark , or by the Inuit name eqalussuaq , is a large shark of the family Somniosidae -LRB- `` sleeper sharks '' -RRB- , closely related to the Pacific and southern sleeper sharks . The distribution of this species is mostly restricted to the waters of the North Atlantic Ocean and Arctic Ocean .   It has the longest known lifespan of all vertebrate species -LRB- 392 ± 120 years -RRB- , and is among the largest extant species of shark . 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 .