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[citation needed] Most shark species have five gill slits on each side, however, some species can have up to six or seven like the sixgill sawshark and sharks in the order Hexanchiformes. [40] As part of their respiratory system, sharks also have an accessory respiratory opening called a spiracle behind their eyes.
In elasmobranchs (sharks and rays) the spiracle bears a small pseudobranch that resembles a gill in structure, but only receives blood already oxygenated by the true gills. [7] The function of the pseudobranch is unknown, but it is believed that it supplies highly oxygenated blood to the optic choroid and retina and may have baroreceptor ...
Shark finning yields are estimated at 1.44 million metric tons (1.59 million short tons) for 2000, and 1.41 million metric tons (1.55 million short tons) for 2010. Based on an analysis of average shark weights, this translates into a total annual mortality estimate of about 100 million sharks in 2000, and about 97 million sharks in 2010, with a ...
The entire body of a shark is a very efficient eating machine. Each organ has been fine-tuned for hunting and acquiring food.
The simpler structure is found in jawless fish, in which the cranium is represented by a trough-like basket of cartilaginous elements only partially enclosing the brain, and associated with the capsules for the inner ears and the single nostril. [9] Cartilaginous fish, such as sharks, also have simple skulls.
Baleen whales have two blowholes positioned in a V-shape, while toothed whales have only one blowhole. [6] The blowhole of a sperm whale , a toothed whale, is located left of centre in the frontal area of the snout, and is actually its left nostril, while the right nostril lacks an opening to the surface and its nasal passage is otherwise well ...
With his hand close to razor sharp teeth, shark expert Neil Harvey attempts tonic immobility in a large reef shark. Tonic can be induced by turning a shark upside down, but that's not the only way.
The shape of the hammerhead shark's head may enhance olfaction by spacing the nostrils further apart. Sharks have keen olfactory senses, located in the short duct (which is not fused, unlike bony fish) between the anterior and posterior nasal openings, with some species able to detect as little as one part per million of blood in seawater. [61]