Cookiecutter shark

Cookiecutter shark
Conservation status
Least Concern  (IUCN 3.1)[1]
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Subclass:	Elasmobranchii
Subdivision:	Selachimorpha
Order:	Squaliformes
Family:	Dalatiidae
Genus:	Isistius
Species:	I. brasiliensis
Binomial name
Isistius brasiliensis (Quoy & Gaimard, 1824)
Range of the cookiecutter shark
Synonyms
Isistius labialis Meng, Chu & Li, 1985 Leius ferox Kner, 1864 Scymnus brasiliensis Quoy & Gaimard, 1824 Scymnus torquatus Müller & Henle, 1839 Scymnus unicolor Müller & Henle, 1839 Squalus fulgens Bennett, 1840

The cookiecutter shark (Isistius brasiliensis), also called the cigar shark, is a species of small squaliform shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded as deep as 3.7 km (2.3 mi). It migrates vertically up to 3 km (1.9 mi) every day, approaching the surface at dusk and descending with the dawn. Reaching only 42–56 cm (16.5–22 in) in length, the cookiecutter shark has a long, cylindrical body with a short, blunt snout, large eyes, two tiny spineless dorsal fins, and a large caudal fin. It is dark brown, with light-emitting photophores covering its underside except for a dark "collar" around its throat and gill slits.

The name "cookiecutter shark" refers to its feeding method of gouging round plugs, as if cut out with a cookie cutter, out of larger animals. Marks made by cookiecutter sharks have been found on a wide variety of marine mammals and fishes, and on submarines, undersea cables, and human bodies. It also consumes whole smaller prey, such as squid. Cookiecutter sharks have adaptations for hovering in the water column, and likely rely on stealth and subterfuge to capture more active prey. Its dark collar seems to mimic the silhouette of a small fish, while the rest of its body blends into the downwelling light via its ventral photophores. When a would-be predator approaches the lure, the shark attaches itself using its suctorial lips and specialized pharynx and neatly excises a chunk of the flesh using its bandsaw-like set of lower teeth. This species has been known to travel in schools.

Though rarely encountered because of its oceanic habitat, a handful of documented attacks on humans were apparently caused by cookiecutter sharks. Nevertheless, this diminutive shark is not regarded as dangerous to humans. The International Union for Conservation of Nature has listed the cookiecutter shark under least concern, as it is widely distributed, has no commercial value, and is not particularly susceptible to fisheries.