Coral catshark
(Atelomycterus marmoratus)
 

Guitar fish
(Rhina ancylostoma) (ray)

Zebra shark
(Stegostoma fasciatum)

Guitar fish
(Rhynchobatus djiddensis) (ray)
 

Bigeye thresher shark
(Alopias superciliosus)

Japanese horn shark
(Heterodontus japonicus)

Hammerhead shark
(Sphyrna lewin)

Sorrah shark
(Carcharhinus sorrah)

Greyspotted catshark
(Asymbolus analis)

Spotted bamboo shark
(Chiloscillium plagiosum)

MUSEUM SHARKS

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SHARKS
Sharks, together with races, torpedos and chimeras, are fishes belonging to the class of the condroittis (Chondroichthyes) and they are present in all the seas of the globe, from the surface up to 1500 meters deep, from the warm tropical waters, to the colds arctic and Antarctic seas.

There are about 350 kinds of Sharks, an about fifty of which present in the Mediterranean, with dimensions that go from the only 25 cm. of the Pygmy Shark from the ribbon tail (Eridacnis radcliffei) to the 18 meters of the Whale Shark (Rhincodon typus), that represents with these measures also the greatest fish actually known.
The most ancient fossils of these animals go up to around 400 million years, and the biologist thinks that their evolution has even already arrived at the most level 100 million years ago.
The skeleton of the sharks is not bony, as that of the common fishes but cartilaginous, formed by cartilage, similar to that that constitutes the ear or the human trachea.
Contrarily of the common fishes, the sharks don't possess the swimming bladder (an inside afloat body that can fill him with gas) whose function of support to the floating is replaced partly from the big liver, that can reach the 25% of the animal weight. Sharks are predators and in their diet it can be present fish, smaller shark, shellfish, mollusc and sea mammal.

The biologist knows three kinds of sharks that eat plankton, filtering the water that enters from their jaws. They are the already quoted Whale Shark (Rhincodon typus, up to 21 m.) Elephant Shark (Cetorhinus maximus, up to 13 m.) and the Great mouth Shark (Megachasma pelagios, up to 5 m.).  Sharks form is generally tapered and hydrodynamic, with the lengthened face and pointed, to favor the advancement in water.
 

Sharks possess the same senses of the man, more other two to us strangers, that are the ability to perceive the electric fields and the waves of pressure spreaded in water.

Taste: the sense of the taste in the sharks is insured from the presence, in the mouth, but also on the surface of their skin, of gustatory papille similar to those human. The shark therefore, can also use this sense with the simple contact of the bodily surface.

Touch: along sharks body there are sensorial cells that are in deep relationship with the gustatory papilles and let the shark realizes when a physical contact happens.

Hearing: in the sharks it is present an inside ear, with the ability to perceive above all sounds of low frequency as those sent forth by wounded animals, and therefore potential preys for this superb animal.

Sense of smell: the sharks nostrils, always well visible on the inferior part of the face, are constituted by two channels to blind fund, at the end there are cells that analyze the presence of fragrant substances dissolved in water. The sensibilitynof the sharks is very developed, it is thought that a shark can individualize 1 part of blood in 100 million parts of water.

Sight: the sight of the sharks, contrarily to the popular thought, is very developed. The pupil can tighten or to widen in base to the light quantity, and in many sharks it is present, behind the retina, the tapetum lucidum, a series of reflecting plates that amplify the light andallow the sight also during the night. Under conditions of strong illumination the tapetum lucidum is darkened, not to dazzle the retina and to also provoke irreversible damages.

Side lines: the side lines, one for every side of the shark, are constituted by sensorial cells that give the ability to perceive the waves of pressure owed to the movements of the water.

Ampullae Lorenzinii: they are of the organs that take contact with the outside through small and numerous holes, present especially in the region of the head, full of a gelatinous conductor substance, in communication with nervous terminations. In this way the shark has the ability to perceive the electric fields produced by the animals (therefore individualize preys under the sand) and probably to recognize their position in comparison to the magnetic earth fiels.

Sharks teeth are the most known part of these fishes, they constitute further a present element in the descriptions and in the images that have to strike our imagination. The teeth are similar to the placoid scales that dress the shark body; they are modified and of greater dimensions, not anchored to the cartilage of the jaws, but simply fixed in the derma by fibers of connective fabric. They are externally dressed again by an enamel that is very hard and resistant for the almost total absence of organic substance. The enamel protects a layer of dentina inside which the pulp is found, rich of blood vases. In the sharks jaws the teeth are prepared in more file, six and the last toward the inside of the mouth are generally tilted, covered by a fold of fabric and not yet completely developed. During the growth the tooth is subject to a move in ahead for the continuous formation of the gengival fabric to which is connected. In their advancement they progressively straighten, because of the simple mechanical tension, until they don't become entirely functional. After a few times the teeth of the anterior lines are destined to fall, following traumatic breakups or spontaneously and the biologist think they are singly replaced every 8-15 days, more frequently in the youngest samples. The biologist think that some kinds of sharks renew a whole line of teeth to the time.

Unlike other characters the teeth of the sharks have forms and very different dimensions, due to the alimentary habits of every kind, even if the preys are almost swallowed without mastication. They can be long and pointed, sharp, wide, of triangular form and with serrated edges: each of these solutions is proper to a particular type of prey. The teeth of the superior jaw are often different from those of the inferior jaw, to be able to make the most effective bite. Generally the superior teeth, direct to shear the preys, are greater, while those inferior, that have to furnish the maximum taking, are thinner and pointed. For the different forms and dimensions the teeth are held useful elements to the recognition of the kinds and in some cases even of the sex. Some experiments have been realized for appraising the strength engraved by the bite of a Carcharhinus: it results of around 3 tons for square centimeter and the sturdiness of the teeth has been compared to that of steel.
 

Many aspects of the sharks biology and ethology are not very well known, above all because of the difficulty to study these fishes in their natural environment and for their bashful and solitary behavior.. Here you will find some questions on the life of the sharks that don't have had answered ..

It seem that the pressure practiced by the bite of a shark Carcharhinus obscurus of around two meters is three tons for square centimeter! To that value could arrive then that of a white shark of the length of seven meters?!

According to Walter Starck the strips coloration white and black horizontal, that reproduces that poisonous snakes of sea can be used as anti-shark protection in the cases in which it is had to be to narrow contact with these animals (es: taken back video, search, etc.).
The author remembers, to confirmation of this, the coloration of the pilots fish that often accompanies the sharks in their swimming and the declarations of the king of the island Tonga that makes to paint his people to white and black strips before plunging themselves in sea to fish. Can these explanations have therefore a scientific value??

The shark Carcharhinus longimanus is usual to follow the Globicephala macrorhyncus that swims and moves in numerous flocks. The delfinidis, because of the great dimensions, don't come certain considered preys from these sharks.. Which is the explanation of this behavior, really very particular??

The hammer shark Sphyrna lewini, normally solitary, has been observed to swim, in the reefs of Sanganeb in Red Sea, in numerous flocks, with the adult samples to the outside and the young people to the center.. Surely these sharks don't have to unite themselves in flocks to avoid the raiders, and probably they don't even do it for reproductive motives.. Which is therefore the explanation??

In the website www.prionace.it you can continue to read all the informations about sharks biology and etology, with images, video, news, and more about these marvellous animals..