What is a Shark?
This term there are other uses, see Shark (disambiguation) .
Sharks (lat. Selachii )  is a superorder of cartilaginous fish ( Chondrichthyes ) belonging to the elasmobranch subclass ( Elasmobranchii ) and has the following distinctive features: elongated body, more or less torpedo-like shape, large heterocercal caudal fin, usually a large number of sharp teeth in each jaw  .
The skeleton of sharks is markedly different from the skeleton of a bony fish — it has no bones. and it is fully formed from cartilaginous tissue. In the skeleton there are the following departments:
Axial skeleton — the spine. educated numerous ampicillinum cartilaginous vertebrae ;
The skull with two divisions — the brain box and the skeleton of the mouth and Gill apparatus;
The paired appendages and girdles — pectoral and pelvic fins ;
Unpaired fins are, as a rule, caudal, anal and two dorsal fins.
Through the channels of the vertebra is the chord. penetrating the entire spine. The skull of the shark is a solid cartilaginous box, the front end thereof is elongated in a rostrum that supports the snout. On the sides are sockets that protect eyes, between the walls of the eye sockets is the brain .
The belt of the front legs is a cartilaginous arch, lying in the thickness of masculinising behind the Gill of the Department, and may not be associated with axial skeleton. On the side of the belt is growth, which is the home of prihlasenia of the skeleton of the fin. Belt pelvic fins has the form of a cartilaginous plate that forms the muscles of the abdominal cage in front of the cloaca. To the side of prichlenyaet the skeleton of the pelvic fin, which consists of a single elongate basal element attached near the radial cartilages. In males, the basal element is the skeletal basis of pterygophobia — copulatory outgrowth.
Skeleton unpaired fins consists of radialiy immersed in the muscles and penetrating into the base of the fin. Tail fin heterocercal, and in the upper blade comes to the end of the spinal column. The blades of the fins are supported by elastodiene.
Placoid scales. characteristic of the shark among the fishes is the most ancient in phylogenetic terms . The scales are rhombic plates, which end in a spike, protruding from the skin outwards. According to the structure and strength scales close to the teeth. that gives reason to call her dermal denticles. These teeth have a wide base, flattened shape and very vividly delineated crown. Most crowns are very sharp and closely adjacent to each other, so the skin may seem relatively smooth, if you run your hand from head to tail or Vice versa, or rough, like sandpaper — if you run in the opposite direction. The mineral part is represented by dentin. educated cells of the corium. connective tissue which pervades the base of scales. The composition of the dentin close to the bone, but denser. Dentine layer of teeth is composed of solid mineral Apatite. dressed in collagen. Thanks to the microstructure of the teeth have a hardness and resiliency that provides the shark a good protective shell (like from larger animals, including other sharks and small parasites ), and at the same time do not create interference for high mobility — like chain mail. Spike placoid scales is also characterized by a higher strength, because the outside is covered with the special enamel — microdontia formed by the cells of the basal layer of the epidermis. Placoid scale has a cavity filled with loose connective tissue with blood vessels and nerve endings .
The combination of shape, position and composition of the dermal denticles plays a significant role in streamlining the body of the shark. For example, pronounced the raised grooves on these teeth in white sharks create a hydrodynamic effect that is comparable to the aerodynamic effect, which occurs when the motion of the Golf ball. The presence of tiny protrusions and cavities as a result significantly reduces turbulence. The shape, structure and size of teeth vary among different species of sharks. According to scientists, the most rapid skin types reduces water resistance by up to 8 % . Mako shark. sheresheva scales that can further reduce the resistance, which allows it to accelerate to 80 km/h . In addition, hydrodynamic properties of teeth provide a very useful effect, the hunter — silent operation. Unlike bony fishes, fins which generate during the movement of sound waves, the movements of white sharks in pursuit of prey remain almost inaudible to her victims almost to the time of the attack.
Some of the heart muscle is continuously working in the heart;
Visceral muscles are functioning in the arteries and other internal organs;
The somatic muscles, resulting in movement of the body, is divided, in turn, on:
Functionally it can be divided into the muscles of the fins, the musculature of the head from the Gill and jaw apparatus and the muscles of the digestive system and internal organs. The sharks all muscles of the body (somatic) consists of a series of muscle segments — momirov, which are separated from each other misatake. The musculature of the fins formed by separate bundles of muscle. Feature of muscle is its relative autonomy, that is, it retains the ability to cutbacks even when a communication failure with the Central nervous system   .
Teeth and jaw
The teeth of most sharks are in the shape of sharp cones and sit on the cartilage of the upper and lower jaws. The teeth are replaced regularly as loss in the pipeline — their replacement is constantly growing from the inside. According to its structure and origin is modified placoid scales . Depending on diet and lifestyle teeth and jaws are very different in different species of sharks. Demersal sharks, which generally food secure hard shell, have grinding teeth with flat ribbed surface (raznosoly shark ). Many predatory species have long, sharp teeth, adapted for slight penetration into the flesh of the prey (e.g., sand sharks ). These sharks, like tiger. teeth broad and serrated — designed for cutting and tearing meat heavy toll. The plankton eating sharks, the teeth are small (about 3 — 5 mm at whale shark