Cookiecutter shark

2007 Schools Wikipedia Selection. Related subjects: Insects, Reptiles and Fish

iCookiecutter shark
Drawing by Dr Tony Ayling
Conservation status
Least Concern (LC)
Scientific classification
Kingdom: Animalia Subkingdom: Deuterostomia Phylum: Chordata Class: Chondrichthyes Subclass: Elasmobranchii Order: Squaliformes Family: Dalatiidae Genus: Isistius Species: I. brasiliensis
Binomial name
Isistius brasiliensis ( Quoy & Gaimard, 1824)

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

Naming

It gets its name from its feeding style which often creates perfect "cookie-cutter" shaped plugs in the skin of large marine mammals and other large sharks.

Habitat and distribution

Worldwide in deep water. The cookiecutter shark has been found at depths of about 1,000 m (3,300 ft) below the surface of the ocean.

Anatomy and appearance

The cookiecutter 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).

Diet

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 a parasite.

Reproduction

Cookiecutter sharks reproduce through aplacental viviparity in the same way as great white sharks. Little else is known about their reproduction.

Interaction with humans

There has been little interaction between humans and the cookiecutter shark. However, there was an incident in which a cookiecutter shark took a bite out of a 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.