Sharks are the most ancient predators who appeared on the planet more than 450 million years ago. Since then they not strongly changed. Sharks – some of the few living beings causing in the person the greatest fear for the life.
Instruction
1. The majority of sharks trunks have the extended and spindle-shaped form. Color of their skin depends on a species of the fish and can be blue or gray, even white (a white shark). Some sharks in general are painted in spots or strips (for example, a tiger shark). Their head has a peculiar lengthening in the form of a nasal outgrowth which is called rostrumy. On each side the heads of a shark are located gills – several cracks through which there passes the water enriched with oxygen. Ancient species of sharks of these cracks usually have about 5 pieces from each party, and at modern – up to 7 pieces. Eyes at sharks black and big. They settle down the heads on each side. Behind eyes it is possible to see two openings conducting in a throat. Ichthyologists call them the bryzgalets representing rudiments of branchiate cracks.
2. It is curious that in a body of sharks there is no real bone. Their skeleton entirely consists of cartilages, and skin at most of representatives of these terrible predators is covered with quite sharp thorns. It should be noted that inhabitants of some islands and peninsulas use such sharkskin as grinding material for polishing of a tree. Pair extremities of sharks are the chest and belly fins located horizontally. The tail fin – raznoplastovy, and its form at different types of sharks differs. It is connected with certain conditions of dwelling of any given species of these fishes. It should be noted that sharks are the fishes who do not have a swimming bubble. Other bodies compensate negative buoyancy: the increased liver, fins and a cartilaginous skeleton.
3. The mouth at sharks is in the lower part of the head. It is not absolutely convenient for the fish: to grab the production, it should be developed sideways or in general on a back. Teeth at the majority of these creations very large, sharp and jagged at the edges. They have the cone-shaped form. Distinctive feature of jaws of all sharks is the non-standard arrangement of teeth: they settle down in five (or even in seven) ranks. Besides, teeth of these fishes are easily regenerated in case of breakage during six times for all life.
4. Sharks are found practically in all oceans and the seas of the planet. These fishes are the most ancient on Earth. Now them there are more than 450 types – and these are not all types known to science. Sharks are very gluttonous fishes, there is even a saying: that a wolf on the land, a shark in water. Many of these fishes the whole packs float behind vessels and the ships waiting that in water something edible will fall and not really. The fact is that they can swallow of everything: both cans, and empty bottles, and other stuff. If to speak about record-holder sharks, then as the smallest shark in the world it is recognized deep-water, length of her trunk is only 17 cm, and the biggest – a harmless whale shark with a length of body of 20 m.