The Cookiecutter Shark (Isistius brasiliensis) is a small, slow-swimming shark. The cookiecutter is also known as the cigar shark (due to its color and shape), the luminous shark (because it emits a green glow from its belly), and the Brazilian shark. It is a large-eyed predator that lives in deep tropical ocean waters worldwide, at depths of about 3500 m.

Anatomy: This brown shark grows to be about 20 inches (50 cm) long and has a blunt snout. The dorsal fin is small and closer to its tail than on most sharks. The large eyes have green pupils. It is harmless to humans and is rarely even seen by divers. The belly of the cookiecutter shark has a small patch of bioluminescence on it. This patch is thought to lure fish to it in the dark, deep ocean environment. Hungry fish think the cookiecutter is a smaller fish than it is (because the patch is smaller than the cookiecutter and that is all they can see in the dark); the cookiecutter can then ambush and bite the surprised "hunter." The cookiecutter reproduces via aplacental viviparity, but little else is known about its reproduction.

Teeth and Diet: The cookie-cutter shark eats by taking round (cookiecutter-shaped) bites out of its victims with its long teeth and powerful jaws, mostly attacking large fish and whales (including dolphins). In an attack, the cookiecutter shark's lips attach to its victim like a suction cup (creating a vacuum). It then uses saw-like teeth that swivel and take an oval-shaped bite of flesh. The teeth in the lower jaws are large, prominent, and triangular; the teeth in the upper jaws are smaller.

Classification: Kingdom Animalia, Phylum Chordata, Class Chondrichthyes, Order Squaliformes, Family Squalidae (dogfish sharks), Genus Isistius, Species brasiliensis.