Somniosus microcephalus is the largest member of the Somniosidae family, commonly known as the sleeper sharks. The family gets its name from its sluggish swimming speed, and is host to 20 mostly deep water species found across the world.

Species in the Somniosus genus all share very similar body plans, and keys detailing how to differentiate the species often contradict one another and lead to misidentification being common outside of the Arctic. Because of this and the limitations of identifying species from a still image, the true range of the Greenland shark is under debate, and it’s been proposed that the only reliable way to identify them is through genetic testing (Benz et al 2007).

(Benz et al 2007)