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Anatomy of a shark  SKELETON Shark skeleton is markedly different from the skeleton of bony fish - there are no bones, and it is completely formed of cartilage. LEATHER Shark placoid covered with scales, which scales are rhombic plates ending in a spike protruding from the skin outward. According to the structure and strength of scales close to the bone, which gives reason to call it dermal denticles. These cloves have a wide base, flattened shape and very boldly contoured crown. The majority of crowns are very sharp and fit snugly to each other, so the skin may appear relatively smooth, if you run your hand from the head to the tail, and vice versa - a rough, like sandpaper - if the conduct in the reverse direction. Teeth and jaws The teeth of most sharks are in the form of acute dentine and cones sitting on the cartilage of the upper and lower jaws. The teeth are regularly replaced as the loss or wear and tear on the principle of the assembly line - to replace them constantly grows on the inside. According to their structure and origin is modified placoid scales. Depending on the diet and lifestyle of the teeth and jaws are very different in different species of sharks. Benthic sharks, food which is usually protected by a hard shell, are hundreds of small smooth teeth. Pelagic species peculiar to the presence of very sharp teeth are adapted for easy penetration into the flesh of prey. Such sharks like tiger, teeth nozheobraznoy forms for tearing meat of the victim. Do sharks feed on plankton small vestigial teeth. Teeth of the Tiger Shark     BUOYANCY Unlike bony fish, sharks have no swim bladder. Instead compensate for negative buoyancy helps them huge liver, cartilage, bones and fins. Most shark species need to move constantly in order to maintain breathing, so could not sleep for a long time. However, some species, such as nurse sharks, nurse, able to pump water through their gills, allowing them to rest on the bottom. DIGESTIVE SYSTEM After a hearty meal, the sharks are able to starve for a long time, slowly and sparingly spending accumulated resources, and in general their need for food is relatively small. For example, captive three-meter Australian sand shark weighing 150 kg per year ate just 80-90 kg of fish. The Sharks periodically produce eversion of the stomach - evert it out through the mouth into the aquatic environment with the aim of cleansing. It is interesting that at the same time never hurt stomach with numerous teeth. SMELL Smell sharks? One of the main sensor system. Experiments have shown high sensitivity to smells sharks. Agencies represented nostrils smell? small bags on the face, transmit water to the olfactory receptors. The sense of smell is involved in the search and production partner for reproduction. In white shark for the sense of smell is used 14% of the brain. A particularly well-developed sense of smell hammerhead sharks? spaced a good distance from each other on the head a peculiar form of the nostrils allow to better define the direction of the source of the smell. Studies have shown that sharks are more responsive to smells wounded or alarmed production. Sharks are able to pick up the scent of blood, diluted in a ratio of 1: 1 000 000, which can be roughly compared with one teaspoon of the swimming pool is medium in size. VISION Structure of a shark's eyes for the most part the same as in all vertebrates, but with a difference. Eye of the sharks has a special reflective layer? tapetum? located behind the retina. Tapetum passed through the retina sends light back so that it once again working on receptors, thus increasing the sensitivity of the eye. This significantly increases visual acuity, especially in low light conditions. Another feature of some species is the presence of blinking century which closes the eye directly in the attack on the victim, protecting it from damage. Sharks without blinking century, when attacking the victim roll their eyes. It was previously believed that sharks eye contains too little cone and can not distinguish color and detail. However, modern technology has allowed to prove the opposite. Visual acuity of some shark species sharper human up to 10 times. HEARING The organ of hearing in sharks? the inner ear is enclosed in a cartilaginous capsule. Sharks perceive predominantly low sounds 100-2500 Hz. Most sharks are able to distinguish between infrasound at a frequency below 20 Hz. The inner ear is also a balance of authority. ELECTRICAL AND magnetoreception Elektroretseptorny apparatus sharks represented ampoules Lorenzini? It is immersed in a small skin connective tissue capsule emanating from these tubes, which open on the surface of the skin. Sharks react to the electric field strength of only 0.01 mV / cm. Therefore, they are able to detect the victim on the electric fields generated by the work of the respiratory muscles and heart.