Cookie-cutter shark

The cookie-cutter shark, Isistius brasiliensis, also known as the cigar shark or luminous shark, is a small rarely-seen dogfish shark.

Anatomy and morphology
Cookie-cutter sharks often glow green and grow up to 50 cm (20 in) long. The underside of the shark is bioluminescent, glowing a pale blue-green that matches the background light from the ocean's surface that serves as camouflage to creatures beneath it. However, a small non-luminescent patch appears black, deceiving the shark's prey, smaller predatory fish (like tuna), into thinking the shark is an even smaller fish. When the predatory fish tries to strike at the shark, the shark strikes back, scoring itself another meal. This is the only known instance whereby a bioluminescent lure is created by the absence of luminescence (contrast with anglerfish).

Distribution
Worldwide in deep water. The cookie-cutter shark has been found at depths of about 1,000 m (3,300 ft).

Feeding ecology
It derived its name from its habit of removing small circular chunks of flesh from whales and large fish. It is hypothesized that the shark seizes its much larger prey with its jaws, then rotates its body to achieve a highly symmetrical cut. They are considered parasites.

Life history
Cookie-cutter sharks reproduce through aplacental viviparity in the same way as great white sharks. Little else is known about their reproduction.

Etymology and taxonomic history
Its name comes from its feeding style which often creates perfect "cookie-cutter" shaped plugs in the skin of large marine mammals and other large sharks (as well as the rubber coating of submarines).

Interaction with humans
There has been little interaction between humans and the cookie-cutter shark. However, there was an incident in which a cookie-cutter shark took a bite out of the rubber sonar dome of a US Navy submarine, causing damage to the housing, and forcing the submarine out of service until the rubber could be replaced.