Somniosid

Somniosid is a family of sharks belonging to the order Squaliformes. This family is commonly known as sleeper sharks. They are characterized by their slow-moving nature and their large, ovate bodies. Sleeper sharks are found in cold, deep waters across the world's oceans, primarily in the Arctic and Antarctic regions, as well as in temperate and tropical waters at extreme depths. They are among the largest of the living shark species, with some individuals exceeding 6 meters in length.

The diet of somniosids is varied and includes fish, squid, seals, and carrion. They are considered apex predators in their environments. Their eyes are relatively small for their size, and they possess a unique olfactory system that aids in detecting prey in low-light conditions. Sleeper sharks have two dorsal fins and an anal fin, but lack a caudal fin's upper lobe, giving them a distinctive asymmetrical tail.

One of the most remarkable aspects of somniosids is their exceptionally long lifespan. The Greenland shark, a prominent member of this family, has been estimated to live for several centuries, making it one of the longest-lived vertebrates known. Their slow metabolism is thought to contribute to this longevity. Reproduction in somniosids is ovoviviparous, meaning the eggs hatch inside the mother, and the pups are born live. Little is known about their reproductive habits due to their elusive nature and deep-sea habitat.