Name: cookiecutter shark
Scientific Name: Isistius brasiliensis
FAQ:
The cookiecutter shark , also called the cigar shark, is a species of small dogfish shark in the family Dalatiidae. This shark occurs in warm, oceanic waters worldwide, particularly near islands, and has been recorded from 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. GROWTH:Reaching only 42–56 cm (17–22 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 in color, 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 habit of gouging round plugs, like a cookie cutter, out of larger animals. Marks made by cookiecutter sharks have been found on a wide variety of marine mammals and fishes, as well as on submarines, undersea cables, and even 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 flesh using its bandsaw-like set of lower teeth. This species has been known to travel in schools.The intrinsic green luminescence of the cookiecutter shark is the strongest known of any shark, and has been reported to persist for three hours after it has been taken out of water .The ventrally positioned photophores serve to disrupt its silhouette from below by matching the downwelling light, a strategy known as "counter-illumination", that is common among bioluminescent organisms of the mesopelagic zone. The individual photophores are set around the denticles and are small enough that they cannot be discerned by the naked eye, suggesting that they have evolved to fool animals with high visual acuity and/or at close distances.Set apart from the glowing underside, the darker, non-luminescent collar tapers at both sides of the throat and has been hypothesized to serve as a lure by mimicking the silhouette of a small fish from below. The appeal of the lure would be multiplied in a school of sharks. If the collar does function in this way, the cookiecutter shark would be the only known case of bioluminescence in which the absence of light attracts prey, while its photophores serve to prevent premature detection by incoming would-be predators. As the shark can only match a limited range of light intensities, its vertical movements likely serve to preserve the effectiveness of its disguise across various times of day and weather conditions.DIET: Virtually every type of medium to large-sized oceanic animal sharing the habitat of the cookiecutter shark is open to attack: bite scars have been found on cetaceans, dugongs, sharks, deepwater stingrays, and bony fishes. The cookiecutter shark also regularly hunts and eats entirely squid
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