Cookie Cutter sharks glow
The cookie cutter shark (also known as the cigar shark or luminous shark), is a small rarely-seen dogfish shark. It derived its name from its habit of removing small circular chunks of flesh from whales and large fish. Scientists believe that the shark bites onto its much larger prey with its jaws, then rotates its body to achieve a symmetrical cut. It is considered a parasite.
The underside of the cookie cutter shark is bio-luminescent (which is the production of light by living organisms) and glows a pale blue-green. The glowing acts as a form of camouflage from creatures beneath it because it matches the background light from the water’s surface.
In addition to camouflage, the luminescence also helps the cookie cutter shark attract its next meal. There is a small non-luminescent patch on the cookie cutter’s underside that appears black. This “black” spot appears to smaller predatory fish, like tuna, to be an even smaller fish. The fish will then approach the cookie cutter and strike at what it thinks is a smaller prey fish. However, it is rudely surprised when the shark strikes back.
This is the only known instance where a bio-luminescent lure is created by the absence of luminescence.
