This tiny, glowing shark takes circular bites out of animals much larger than itself.

Nature · Published 3 October 2026 Swipe more like this →

In short: The cookiecutter shark is a master of deception. By using bioluminescent photophores to mimic a small fish, it lures unsuspecting predators into range. Once they approach, the shark attaches with suctorial lips and uses its serrated teeth to carve a perfect, cookie-shaped plug of flesh from its target.

Named for the distinctive, circular wounds it leaves on prey, the cookiecutter shark (Isistius brasiliensis) is a small, cigar-shaped predator that thrives in the deep ocean. While it can reach depths exceeding 3,281 feet (1,000 meters) during the day, it performs a daily vertical migration to surface waters at night to hunt. This species is found in warm, oceanic waters across the globe, from the Atlantic to the Indo-Pacific.

The shark's hunting strategy relies on stealth and bioluminescence. Its underside is covered in light-producing organs called photophores, which emit a greenish glow. This light mimics the silhouette of a small fish, attracting larger marine life like tuna, whales, and even other sharks. When a larger animal investigates the lure, the cookiecutter shark latches on with specialized suctorial lips. It then rotates its body, using its lower jaw—which functions like a bandsaw—to excise a precise chunk of flesh.

Despite its aggressive feeding habits, the cookiecutter shark is considered harmless to humans due to its small size and deep-water habitat. Males typically grow to about 16.5 inches (42 cm), while females reach up to 22 inches (56 cm). Interestingly, the shark sheds its lower teeth as a complete, interconnected unit rather than individually, and it is believed to ingest these shed teeth to help maintain its internal calcium levels.

Historically, the origin of these mysterious wounds was misunderstood. Ancient Samoan legends attributed them to sacrifices made by tuna, while later theories blamed lampreys or parasites. It was not until 1971 that researcher Everet Jones identified the cookiecutter shark as the culprit. Today, the species remains of little commercial importance, though it is occasionally noted for causing damage to submarines and undersea cables.

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