Which shark is known for glowing photophores on its underside?

The cookiecutter shark is known for glowing photophores on its underside.

Photophores are light-producing organs. In the cookiecutter shark, they create a blue-green glow across much of the lower body, while a darker collar-shaped area breaks up the outline near the throat. This counterillumination can make the shark harder to see from below against the faint light filtering down from the surface.

The species is small, usually less than 60 centimetres long, but it has a remarkable feeding method. Its rounded jaws remove plug-shaped pieces of flesh from whales, dolphins, large fish, and occasionally submarines or other artificial objects. The wounds resemble cuts made with a cookie cutter, giving the shark its common name.

Bioluminescent sharks are not the same as sharks that merely reflect light. The cookiecutter’s glow comes from living photophores containing biochemical light-producing systems. Several deep-sea shark species also glow, but the cookiecutter is particularly famous for its combination of bioluminescence and circular bites.