越详细分越高
鲨鱼属于脊椎动物门软骨纲(Chondrichthyes)板鳃亚纲，海生，少数种类进入淡水，为一群游速快的中大型海洋鱼类。
Sharks are vertebrates steel door cartilage (Chondrichthyes) elasmobranchii, Marine, a few species enter fresh water, as a group of large Marine fish speed is fast.
鲨内骨骼完全由软骨组成，常钙化，但无任何真骨头组织，外骨骼不很发达或退化，身体常被皮齿(质鳞)，牙多样化，具有硬肌，但膜骨则永不存在，脑颅无缝。
Shark endoskeleton completely composed of cartilage, often calcified, but without any true bone tissue, degraded or exoskeletons is not very rich, the body is often skin teeth (scale), tooth diversification, with hard muscle, but never exist, membrane bone temple seamless.
上额由腭方软骨组成，下额由梅氏软骨组成。最新研究表明，鲨体内含有多种生物活性成分，如抗癌因子、角鲨烯、黏多糖等等。
On the forehead is composed of palatal side cartilage, the forehead is composed of Mr Medvedev cartilage.Sharks, according to new research in the body contains a variety of biological active ingredients, such as anti-cancer agent, squalene, mucopolysaccharides and so on.
扩展资料
鲨鱼的起源不详，但其地质学纪录可追溯到泥盆纪(4.08亿～3.6亿年前）。鲨鱼化石在中泥盆世出现，在石炭纪（3.6亿～2.86亿年前）成为占优势的脊椎动物。现代鲨鱼出现于侏罗纪早期（2.08亿～1.87亿年前），到白垩纪（1.44亿～6,640万年前）已经发展成现存的各科。
总之，除觅食和游泳机制的改进外，进化对鲨鱼的形态改变甚微。无论对化石种和现存种类来说，牙齿在鲨鱼种类鉴别方面均有很重要作用。
参考资料来源：百度百科-鲨鱼
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第1个回答 2008-03-05
Categories sharks
Chordate door, the door of invertebrates, Chondrichthyes, gill plate subclass, side-Head
According to the 1971 classification system down into Durres
Hexanchiformes Lamniformes Husha head really shark head Squaliform sawshark flat head shark gill shark head wrinkles eight Head
Sharks, some people think that the ocean is the most ferocious animals. Whale sharks to small marine organisms for food, and minke whales almost. The food is similar to some of the biological evolution of a long, and they look very similar whales, this is called "convergent evolution." So "whale shark," the name on the course. Of course, the whale shark is the largest of the existing shark is the largest fish known.
The characteristics of sharks
Sharks physically hard, muscular, with varying degrees of Spindle. Some types of mouth because vary, Tsim Sha Tsui, such as the great white shark and the grey mackerel shark there are also large and round, such as shark and wide Ornithoctonus Ornithoctonus the first shark was flat. Upward vertical tail (caudal fin), a crescent general, most types of the upper tail fin is far greater than the bottom.
Shark swimming rely mainly on the body like a snake with the same movement and organize tail fin like the same swing forward. Stability and control is the use of some of the dorsal fin and horizontal vertical scheduling Xiongqi. Most sharks can not move backward, it is very vulnerable to gill nets such as the obstacles, but it will be difficult to extricate themselves into one. Sharks no swimbladder, so the proportion of these animals mainly by the liver oil in storage to determine. Sharks larger density than water, that is, if they do not actively swimming, it will sink to the seabed. They travel very quickly, but only in a short period of time to maintain high speed. Why not talked about sharks swimbladder, which related to a legend: a long time ago, God created the fish, sharks is only a small fish. God all of a sudden one day I think of the contribution of fish, a fish wanted to reward all swimbladder. But naughty small sharks are in play, wait until after the small sharks know, God has already left. Small sharks can only keep YOU, YOU ah Tour. Vietnam-Vietnam stronger. Millennium, God to inspections, found that the most robust shark find it very strange that he very fair each fish! Why this is the only shark? He asked why the sharks, sharks replied: "Because I was your ancestors did not receive a gift, so he can only travel constantly, the Tour will be strong!"
Sharks 5 ~ each side has seven branchial cleft (unlike we normally bought from the market carp, a fish gill cover Gill), when swimming in the sea through the semi-open mouth inhalation from the branchial cleft outflow of gas exchange. Of the mouth of the shark swimming really looks terrible, but you can not help people breathe? A small number of shark species in the seabed can stop breathing.
Shark research
University of Hawaii marine biologists say they have obtained first-hand evidence that sharks can be aware of the changes in the Earth's magnetic field. The discovery of marine fish in order to prove the existence of an internal "compass" to guide them to distinguish azimuth system provides a new example.
This latest research results published in the British Journal of the Royal Academy of Sciences. University of Hawaii marine biologists - Karl Meyer and his colleagues plotted the design of the pilot. In an artificial environment in the magnetic field training six sandbar sharks and one pair of bun shark. This artificial magnetic field environment is a diameter of 7 meters of the tank, a layer of the external winding copper cables, whenever to put food in the tank, cable switch will be open to simulate the magnetic field environment.
After the six weeks of training, no matter when the switch cable open, even if there is no food to put in the tank, the shark will usually gather to feeding areas. Facts have proved that such a response they feel that the presence of a magnetic field.
Scientists conducting the trial, some of the peculiar habits of sharks has been to allow scientists to speculate that the shark may have special abilities. Husha, blue sharks in the ocean straight to the middle reaches of a long distance, if only with the sense of smell is impossible to achieve. Two-bun shark often gathered in the nearby seamounts, and these mountains are the Earth's magnetic field changes have occurred in the zone.
Scientists hope that the next phase of research is to understand how to identify sharks Earth's magnetic field as well as their degree of sensitivity of the magnetic field sensor. Not long ago, scientists have recognized a number of other animals also have the ability to identify the magnetic field. North Carolina State University researchers proved by experiment, pigeons and the beak on a tiny magnetic particles can help pigeons completed long-distance flights.
Sharks and anticancer
Over the past 20 years, the shark fin market transactions more fire, some 1 million sharks a year cruelly trampled upon. Conservation International Federation in 2004 "endangered species" list, and the new increase at least 10 species of sharks, including the great white shark, the New England gill shark and the Gulf of Mexico kiss white shark. Shark suffered from a number of hunting is an important reason why people accepted the shark cartilage (including the well-known "shark fin") can anticancer wrong propaganda.
According to the Russian News Network recently reported that the United States biological and Johns Hopkins University professor in the Department of Comparative Medicine Jialiaoshitelande in its recently published a research report pointed out that the shark will be the same with cancer. At the same time, consumption of shark cartilage to treat cancer have no apparent effect.
Jialiaoshitelande was of the view that the rise of consumption of shark cartilage is the diet trend is "pseudo-science" through marketing by the victory. He said that the consumption of shark cartilage to treat patients not only unhelpful, shark populations will cause great harm - patients often will blindly believe that these cartilage rejected the therapeutic treatment of other means, hunting activities and wantonly caused the shark The rapid decline in the number of fish.
Sharks have been seen as cancer insulators, cartilage powder being promoted as cancer medicine.
As early as in 1983, the Massachusetts Institute of Technology and two biochemical Boshianen Luobaitelange Lee in the famous American magazine "Science," published an article that shark cartilage in the squalene to the cancer cells can block angiogenesis, and confirmed that can inhibit the growth of cancer cells.
1993, the United States CBS television programme "60 Minutes" invited "sharks never get cancer," the authors Weilianlanshi Dr. shark cartilage can discuss the results of research on cancer, a number of advanced cancer patients in the programme said that taking shark cartilage capsules few weeks after feeling symptoms relieved.
Since then, the cancer that shark cartilage will be through books, articles, websites and vendors widely circulated. Subsequently, the pharmaceutical companies in the market launch of a shark from the connective fibrous tissue made of pills, which claims that shark liver oil capsules "cancer medicine", and created a shark cartilage product sales over 50 million dollar market, the biggest maker of shark cartilage is Weilianboshi son.
1994, the United States Food and Drug Administration (FDA) formally approved the use of shark cartilage products for cancer prevention and control. Therefore, the health of shark cartilage products have become hot commodities on the market, the impact spread to the whole world.
In China, shark cartilage products and the sale of shark soup restaurants were very.
In the late 1990s, the cancer that shark cartilage powder to China. At that time, the market sold shark cartilage products there are two main categories: one category is the physical processing of shark cartilage as lettuce, and the other chemical methods of extraction from the activity.
In addition to vigorously propagate in the former cancer in the number of "active ingredients", also declared that the fineness of lettuce grinding stress how well, fineness must be more than 200 heads can be absorbed into the body, the fineness of the finer the better. What parts of the United States said that the product has reached the fineness of 300 head of lettuce greatly enhance the activity of the active ingredients in the egg quality to the extent of absorption into the body.
The latter claimed that shark cartilage from a very complex organization, a purified extract of two anti-tumor function of angiogenesis inhibitor, and made in accordance with the composition of the shark cartilage capsules, shark cartilage powder Series anticancer drugs. Such drugs in the Chinese market was very popular.
Because sharks have anti-cancer function of this unique community are also eating shark "hot", in particular Hong Kong and Guangzhou and the two restaurants will be selling shark cartilage Aocheng soup, known as the "shark cartilage Chinese soup, "diverse varieties. These restaurants that, in addition to this soup anti-cancer, anti-cancer role, but also Yangyan, beauty, strong bones and tendons, fill the role of the spleen and stomach, and the results go to the people coming in a steady stream.
Recent studies also show that sharks in the cancer itself.
Recent studies have shown that sharks may also suffer from a variety of cancers, including cancer of the cartilage tissue. Jialiaoshitelande Professor total in its report cited 40 examples of tumors with sharks, which overthrew a previous shark cancer is not long.
Dihanhashibage American scientists in the United States Institute of the 91st Session of the annual meeting of cancer that sharks are suffering from cancer. Hashibage is working in the United States National Cancer institutions and scholars, he found that the fish cartilage suffered by the 50 types of cancer, including 23 kinds of cancer is different from the sharks, some of which was directly in the long cartilage.
It is worth noting that the "sharks never get cancer," a book author Dr. Weilianlanshi (he can be regarded as "Shark therapy" Father) has recently admitted that a shark will in fact cancer disease, and to be honest he had come outside the extract of shark cartilage to treat cancer can be the only conclusion is based on an extremely limited number of experimental results.
Clinical results show that shark cartilage powder no cancer effect.
In fact, as of now, in view of the effectiveness of shark cartilage powder cancer clinical trials that are null and void. Denmark to the European scholars submitted by the General Assembly on breast cancer research report said, they found a shark cartilage organization made of the so-called "alternative anti-cancer drug" women, did not receive any drug benefits.
Danish researchers on the use of shark cartilage extracts of 17 suffering from terminal breast cancer patients tested, 17 patients to a large doses of shark liver oil capsules, the daily dose of 24.
After three months, 17 patients, 15 were cancer continues to deteriorate. Another patient in the beginning signs of improvement, but then found in the brain of a new tumor.
In addition, in a separate clinical trial, more than 50 were suffering from breast cancer, lung cancer, prostate cancer, colorectal cancer, and other patients in the use of shark cartilage protein purification, the condition are not significantly improved. Moreover, according to the National Institutes of Health, the study showed that, as shark cartilage protein molecules too, intestinal absorption was not easy, even if absorbed, decomposition will be destroyed.
In the name of health food shark cartilage for cancer there is no effect.
Not long ago, the United States Food and Drug Inspection Bureau on the management of the laboratory and his son William factory action to stop publicizing the "shark cartilage products can be cancer" This unconfirmed false advertising.
United States Federal Trade Commission also ruled that the ban on shark cartilage products of any false propaganda, unless the relevant scientific evidence. Weilianlanshi laboratories required to pay 1 million US dollars for judgement, which 450,000 US dollars by the National Cancer Centre and Weilianlanshi laboratories to jointly hold large-scale clinical trials of shark cartilage, in order to identify the truth.
Scientists believe that the name of a variety of health foods shark cartilage for cancer there is no obvious effect.
Shark fin cancer is "What to eat-what" this unscientific view of a new replica. Even so, not even a human shark suffered by some cancer, and can therefore conclude that the shark products to the treatment of human cancer.
Chordate door, the door of invertebrates, Chondrichthyes, gill plate subclass, side-Head
According to the 1971 classification system down into Durres
Hexanchiformes Lamniformes Husha head really shark head Squaliform sawshark flat head shark gill shark head wrinkles eight Head
Sharks, some people think that the ocean is the most ferocious animals. Whale sharks to small marine organisms for food, and minke whales almost. The food is similar to some of the biological evolution of a long, and they look very similar whales, this is called "convergent evolution." So "whale shark," the name on the course. Of course, the whale shark is the largest of the existing shark is the largest fish known.
The characteristics of sharks
Sharks physically hard, muscular, with varying degrees of Spindle. Some types of mouth because vary, Tsim Sha Tsui, such as the great white shark and the grey mackerel shark there are also large and round, such as shark and wide Ornithoctonus Ornithoctonus the first shark was flat. Upward vertical tail (caudal fin), a crescent general, most types of the upper tail fin is far greater than the bottom.
Shark swimming rely mainly on the body like a snake with the same movement and organize tail fin like the same swing forward. Stability and control is the use of some of the dorsal fin and horizontal vertical scheduling Xiongqi. Most sharks can not move backward, it is very vulnerable to gill nets such as the obstacles, but it will be difficult to extricate themselves into one. Sharks no swimbladder, so the proportion of these animals mainly by the liver oil in storage to determine. Sharks larger density than water, that is, if they do not actively swimming, it will sink to the seabed. They travel very quickly, but only in a short period of time to maintain high speed. Why not talked about sharks swimbladder, which related to a legend: a long time ago, God created the fish, sharks is only a small fish. God all of a sudden one day I think of the contribution of fish, a fish wanted to reward all swimbladder. But naughty small sharks are in play, wait until after the small sharks know, God has already left. Small sharks can only keep YOU, YOU ah Tour. Vietnam-Vietnam stronger. Millennium, God to inspections, found that the most robust shark find it very strange that he very fair each fish! Why this is the only shark? He asked why the sharks, sharks replied: "Because I was your ancestors did not receive a gift, so he can only travel constantly, the Tour will be strong!"
Sharks 5 ~ each side has seven branchial cleft (unlike we normally bought from the market carp, a fish gill cover Gill), when swimming in the sea through the semi-open mouth inhalation from the branchial cleft outflow of gas exchange. Of the mouth of the shark swimming really looks terrible, but you can not help people breathe? A small number of shark species in the seabed can stop breathing.
Shark research
University of Hawaii marine biologists say they have obtained first-hand evidence that sharks can be aware of the changes in the Earth's magnetic field. The discovery of marine fish in order to prove the existence of an internal "compass" to guide them to distinguish azimuth system provides a new example.
This latest research results published in the British Journal of the Royal Academy of Sciences. University of Hawaii marine biologists - Karl Meyer and his colleagues plotted the design of the pilot. In an artificial environment in the magnetic field training six sandbar sharks and one pair of bun shark. This artificial magnetic field environment is a diameter of 7 meters of the tank, a layer of the external winding copper cables, whenever to put food in the tank, cable switch will be open to simulate the magnetic field environment.
After the six weeks of training, no matter when the switch cable open, even if there is no food to put in the tank, the shark will usually gather to feeding areas. Facts have proved that such a response they feel that the presence of a magnetic field.
Scientists conducting the trial, some of the peculiar habits of sharks has been to allow scientists to speculate that the shark may have special abilities. Husha, blue sharks in the ocean straight to the middle reaches of a long distance, if only with the sense of smell is impossible to achieve. Two-bun shark often gathered in the nearby seamounts, and these mountains are the Earth's magnetic field changes have occurred in the zone.
Scientists hope that the next phase of research is to understand how to identify sharks Earth's magnetic field as well as their degree of sensitivity of the magnetic field sensor. Not long ago, scientists have recognized a number of other animals also have the ability to identify the magnetic field. North Carolina State University researchers proved by experiment, pigeons and the beak on a tiny magnetic particles can help pigeons completed long-distance flights.
Sharks and anticancer
Over the past 20 years, the shark fin market transactions more fire, some 1 million sharks a year cruelly trampled upon. Conservation International Federation in 2004 "endangered species" list, and the new increase at least 10 species of sharks, including the great white shark, the New England gill shark and the Gulf of Mexico kiss white shark. Shark suffered from a number of hunting is an important reason why people accepted the shark cartilage (including the well-known "shark fin") can anticancer wrong propaganda.
According to the Russian News Network recently reported that the United States biological and Johns Hopkins University professor in the Department of Comparative Medicine Jialiaoshitelande in its recently published a research report pointed out that the shark will be the same with cancer. At the same time, consumption of shark cartilage to treat cancer have no apparent effect.
Jialiaoshitelande was of the view that the rise of consumption of shark cartilage is the diet trend is "pseudo-science" through marketing by the victory. He said that the consumption of shark cartilage to treat patients not only unhelpful, shark populations will cause great harm - patients often will blindly believe that these cartilage rejected the therapeutic treatment of other means, hunting activities and wantonly caused the shark The rapid decline in the number of fish.
Sharks have been seen as cancer insulators, cartilage powder being promoted as cancer medicine.
As early as in 1983, the Massachusetts Institute of Technology and two biochemical Boshianen Luobaitelange Lee in the famous American magazine "Science," published an article that shark cartilage in the squalene to the cancer cells can block angiogenesis, and confirmed that can inhibit the growth of cancer cells.
1993, the United States CBS television programme "60 Minutes" invited "sharks never get cancer," the authors Weilianlanshi Dr. shark cartilage can discuss the results of research on cancer, a number of advanced cancer patients in the programme said that taking shark cartilage capsules few weeks after feeling symptoms relieved.
Since then, the cancer that shark cartilage will be through books, articles, websites and vendors widely circulated. Subsequently, the pharmaceutical companies in the market launch of a shark from the connective fibrous tissue made of pills, which claims that shark liver oil capsules "cancer medicine", and created a shark cartilage product sales over 50 million dollar market, the biggest maker of shark cartilage is Weilianboshi son.
1994, the United States Food and Drug Administration (FDA) formally approved the use of shark cartilage products for cancer prevention and control. Therefore, the health of shark cartilage products have become hot commodities on the market, the impact spread to the whole world.
In China, shark cartilage products and the sale of shark soup restaurants were very.
In the late 1990s, the cancer that shark cartilage powder to China. At that time, the market sold shark cartilage products there are two main categories: one category is the physical processing of shark cartilage as lettuce, and the other chemical methods of extraction from the activity.
In addition to vigorously propagate in the former cancer in the number of "active ingredients", also declared that the fineness of lettuce grinding stress how well, fineness must be more than 200 heads can be absorbed into the body, the fineness of the finer the better. What parts of the United States said that the product has reached the fineness of 300 head of lettuce greatly enhance the activity of the active ingredients in the egg quality to the extent of absorption into the body.
The latter claimed that shark cartilage from a very complex organization, a purified extract of two anti-tumor function of angiogenesis inhibitor, and made in accordance with the composition of the shark cartilage capsules, shark cartilage powder Series anticancer drugs. Such drugs in the Chinese market was very popular.
Because sharks have anti-cancer function of this unique community are also eating shark "hot", in particular Hong Kong and Guangzhou and the two restaurants will be selling shark cartilage Aocheng soup, known as the "shark cartilage Chinese soup, "diverse varieties. These restaurants that, in addition to this soup anti-cancer, anti-cancer role, but also Yangyan, beauty, strong bones and tendons, fill the role of the spleen and stomach, and the results go to the people coming in a steady stream.
Recent studies also show that sharks in the cancer itself.
Recent studies have shown that sharks may also suffer from a variety of cancers, including cancer of the cartilage tissue. Jialiaoshitelande Professor total in its report cited 40 examples of tumors with sharks, which overthrew a previous shark cancer is not long.
Dihanhashibage American scientists in the United States Institute of the 91st Session of the annual meeting of cancer that sharks are suffering from cancer. Hashibage is working in the United States National Cancer institutions and scholars, he found that the fish cartilage suffered by the 50 types of cancer, including 23 kinds of cancer is different from the sharks, some of which was directly in the long cartilage.
It is worth noting that the "sharks never get cancer," a book author Dr. Weilianlanshi (he can be regarded as "Shark therapy" Father) has recently admitted that a shark will in fact cancer disease, and to be honest he had come outside the extract of shark cartilage to treat cancer can be the only conclusion is based on an extremely limited number of experimental results.
Clinical results show that shark cartilage powder no cancer effect.
In fact, as of now, in view of the effectiveness of shark cartilage powder cancer clinical trials that are null and void. Denmark to the European scholars submitted by the General Assembly on breast cancer research report said, they found a shark cartilage organization made of the so-called "alternative anti-cancer drug" women, did not receive any drug benefits.
Danish researchers on the use of shark cartilage extracts of 17 suffering from terminal breast cancer patients tested, 17 patients to a large doses of shark liver oil capsules, the daily dose of 24.
After three months, 17 patients, 15 were cancer continues to deteriorate. Another patient in the beginning signs of improvement, but then found in the brain of a new tumor.
In addition, in a separate clinical trial, more than 50 were suffering from breast cancer, lung cancer, prostate cancer, colorectal cancer, and other patients in the use of shark cartilage protein purification, the condition are not significantly improved. Moreover, according to the National Institutes of Health, the study showed that, as shark cartilage protein molecules too, intestinal absorption was not easy, even if absorbed, decomposition will be destroyed.
In the name of health food shark cartilage for cancer there is no effect.
Not long ago, the United States Food and Drug Inspection Bureau on the management of the laboratory and his son William factory action to stop publicizing the "shark cartilage products can be cancer" This unconfirmed false advertising.
United States Federal Trade Commission also ruled that the ban on shark cartilage products of any false propaganda, unless the relevant scientific evidence. Weilianlanshi laboratories required to pay 1 million US dollars for judgement, which 450,000 US dollars by the National Cancer Centre and Weilianlanshi laboratories to jointly hold large-scale clinical trials of shark cartilage, in order to identify the truth.
Scientists believe that the name of a variety of health foods shark cartilage for cancer there is no obvious effect.
Shark fin cancer is "What to eat-what" this unscientific view of a new replica. Even so, not even a human shark suffered by some cancer, and can therefore conclude that the shark products to the treatment of human cancer.
第2个回答 推荐于2017-09-21
What is a Shark?
Sharks are a type of fish.
Sharks are amazing fish that have been around since long before the dinosaurs existed. They live in waters all over the world, in every ocean, and even in some rivers and lakes.
Unlike bony fish, sharks have no bones; their skeleton is made of cartilage, which is a tough, fibrous substance, not nearly as hard as bone. Sharks also have no swim bladder (unlike bony fish).
________________________________________
MAJOR DIFFERENCES BETWEEN SHARKS AND BONY FISH
ATTRIBUTE SHARKS
BONY FISH
Skeleton Cartilage only Bones and cartilage
Swimming Can only swim forward. Can swim forwards and backwards
Buoyancy (floating) Large oily liver Gas-filled swim bladder
Gills Gill slits but no gill cover Covered gill slits
Reproduction Eggs fertilized in female's body. Eggs usually fertilized in the water.
Skin Rough, sandpaper-like placoid scales Slippery, overlapping scales
SIZE
A scuba diver above a Whale shark. The Whale shark is the largest fish in the world; the basking shark is the second largest fish.
There are many different species of sharks that range in size from the size of a person's hand to bigger than a bus. Fully-grown sharks range in size from 7 inches (18 cm) long (the Spined Pygmy shark), up to 50 feet (15 m) long (the Whale shark). Most sharks are intermediate in size, and are about the same size as people, 5-7 feet (1.5-2.1 m) long. Half of the 368 shark species are under 39 inches (1 m) long.
________________________________________
BODY SHAPES
Sharks have a variety of body shapes. Most sharks have streamlined, torpedo-shaped bodies that glide easily through the water. Some bottom-dwelling sharks (e.g. the angelshark) have flattened bodies that allow them to hide in the sand of the ocean bed. Some sharks have an elongated body shape (e.g., cookiecutter sharks and wobbegongs). Sawsharks have elongated snouts, thresher sharks have a tremendously elongated upper tail fin which they use to stun prey, and hammerheads have extraordinarily wide heads. The goblin shark has a large, pointed protuberance on its head; its purpose is unknown.
________________________________________
VARIETIES OF SHARKS
There are about 368 different species of sharks, which are divided into 30 families. These different families of sharks are very different in the way they look, live, and eat. They have different shapes, sizes, color, fins, teeth, habitat, diet, personality, method of reproduction, and other attributes. Some types of shark are very rare (like the great white shark and the megamouth) and some are quite common (like the dogfish shark and bull shark). Sharks belong to the group of cartilagenous fish, the Elasmobranchii, that includes the sharks, rays, and skates.
There are over 350 different species of sharks. The spiny dogfish shark is the most common shark.本回答被提问者采纳
Sharks are a type of fish.
Sharks are amazing fish that have been around since long before the dinosaurs existed. They live in waters all over the world, in every ocean, and even in some rivers and lakes.
Unlike bony fish, sharks have no bones; their skeleton is made of cartilage, which is a tough, fibrous substance, not nearly as hard as bone. Sharks also have no swim bladder (unlike bony fish).
________________________________________
MAJOR DIFFERENCES BETWEEN SHARKS AND BONY FISH
ATTRIBUTE SHARKS
BONY FISH
Skeleton Cartilage only Bones and cartilage
Swimming Can only swim forward. Can swim forwards and backwards
Buoyancy (floating) Large oily liver Gas-filled swim bladder
Gills Gill slits but no gill cover Covered gill slits
Reproduction Eggs fertilized in female's body. Eggs usually fertilized in the water.
Skin Rough, sandpaper-like placoid scales Slippery, overlapping scales
SIZE
A scuba diver above a Whale shark. The Whale shark is the largest fish in the world; the basking shark is the second largest fish.
There are many different species of sharks that range in size from the size of a person's hand to bigger than a bus. Fully-grown sharks range in size from 7 inches (18 cm) long (the Spined Pygmy shark), up to 50 feet (15 m) long (the Whale shark). Most sharks are intermediate in size, and are about the same size as people, 5-7 feet (1.5-2.1 m) long. Half of the 368 shark species are under 39 inches (1 m) long.
________________________________________
BODY SHAPES
Sharks have a variety of body shapes. Most sharks have streamlined, torpedo-shaped bodies that glide easily through the water. Some bottom-dwelling sharks (e.g. the angelshark) have flattened bodies that allow them to hide in the sand of the ocean bed. Some sharks have an elongated body shape (e.g., cookiecutter sharks and wobbegongs). Sawsharks have elongated snouts, thresher sharks have a tremendously elongated upper tail fin which they use to stun prey, and hammerheads have extraordinarily wide heads. The goblin shark has a large, pointed protuberance on its head; its purpose is unknown.
________________________________________
VARIETIES OF SHARKS
There are about 368 different species of sharks, which are divided into 30 families. These different families of sharks are very different in the way they look, live, and eat. They have different shapes, sizes, color, fins, teeth, habitat, diet, personality, method of reproduction, and other attributes. Some types of shark are very rare (like the great white shark and the megamouth) and some are quite common (like the dogfish shark and bull shark). Sharks belong to the group of cartilagenous fish, the Elasmobranchii, that includes the sharks, rays, and skates.
There are over 350 different species of sharks. The spiny dogfish shark is the most common shark.本回答被提问者采纳
第3个回答 2008-03-09
Out of all the species walking, flying, slithering or swimming, there aren't many who have been around as long, survived as well, or come in so many shapes and kinds as the shark. The earliest evidences of sharks are isolated spines, teeth and scales that appeared about 430 million years ago in the Silurian Period, known as the "Age of Fishes". Sharks have a sleek, streamlined design which helps them swim without using up a lot of energy.They certainly need to conserve their energy because they never really sleep and most of them never stop swimming.
Some sharks are fierce predators, and would be happy to eat you if they encountered you. Almost any shark six feet or longer is a potential danger, but three species have been identified repeatedly in attacks: the Great White Shark, the Tiger Shark and the Bull Shark . All three live world wide, reach large sizes and eat large prey such as marine mammals or sea turtles. But most sharks never grow longer than five feet and never even see anyone with legs and arms anyway. People kill thousands more sharks every year than sharks kill people.
Sharks take about as long to mature as we do. Some of them become adults in their teens. A mother shark carries her babies inside her body while they develop, sometimes for more than a year. Even so, some sharks are born inside an egg which they have to crack open. They spend early portions of their lives in nursery grounds. Some of the advantages sharks have over people is that they keep growing new teeth, they don't have breakable bones, and they are not prone to get cancer. Sometimes sharks are referred to as swimming computers because of the six senses which they possess: vision, hearing, vibration, smell, taste and electro-perception.
参考资料：
Some sharks are fierce predators, and would be happy to eat you if they encountered you. Almost any shark six feet or longer is a potential danger, but three species have been identified repeatedly in attacks: the Great White Shark, the Tiger Shark and the Bull Shark . All three live world wide, reach large sizes and eat large prey such as marine mammals or sea turtles. But most sharks never grow longer than five feet and never even see anyone with legs and arms anyway. People kill thousands more sharks every year than sharks kill people.
Sharks take about as long to mature as we do. Some of them become adults in their teens. A mother shark carries her babies inside her body while they develop, sometimes for more than a year. Even so, some sharks are born inside an egg which they have to crack open. They spend early portions of their lives in nursery grounds. Some of the advantages sharks have over people is that they keep growing new teeth, they don't have breakable bones, and they are not prone to get cancer. Sometimes sharks are referred to as swimming computers because of the six senses which they possess: vision, hearing, vibration, smell, taste and electro-perception.
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第4个回答 2008-03-05
Sharks (superorder Selachimorpha) are fish with a full cartilaginous skeleton[1] and a streamlined body. They respire with the use of five to seven gill slits. Sharks have a covering of dermal denticles to protect their skin from damage and parasites and to improve fluid dynamics.[1] They have replaceable teeth. They are some of the world's most misunderstood predators, as they very rarely attack humans unless intimidated.
Sharks include species from the hand-sized pygmy shark, Euprotomicrus bispinatus, a deep sea species of only 22 centimetres (9 inches) in length, to the whale shark, Rhincodon typus, the largest fish, which grows to a length of approximately 12 metres (41 feet) and which, like the great whales, feeds only on plankton through filter feeding. The bull shark, Carcharhinus leucas, is the best known of several species to swim in both salt and fresh water (it is found in Lake Nicaragua, in Central America) and in deltas.[2]
Sharks include species from the hand-sized pygmy shark, Euprotomicrus bispinatus, a deep sea species of only 22 centimetres (9 inches) in length, to the whale shark, Rhincodon typus, the largest fish, which grows to a length of approximately 12 metres (41 feet) and which, like the great whales, feeds only on plankton through filter feeding. The bull shark, Carcharhinus leucas, is the best known of several species to swim in both salt and fresh water (it is found in Lake Nicaragua, in Central America) and in deltas.[2]
