The cookiecutter shark (Isistius brasiliensis) is a species of small dogfish shark in the family Dalatiidae. This shark, also called the cigar shark, lives in warm, oceanic waters around the world. It often lives near islands. It has been recorded as deep as 3.7 kilometres (2.3 mi).
The name "cookiecutter shark" refers to its biting. It takes round plugs, as if cut out with a cookie cutter, out of larger animals. Marks made by cookiecutter sharks have been found on many marine mammals and fishes, as well as on submarines, undersea cables, and even human bodies.