Lena睡美梦
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 FISHATTRIBUTE SHARKS BONY FISHSkeleton Cartilage only Bones and cartilageSwimming Can only swim forward. Can swim forwards and backwardsBuoyancy (floating) Large oily liver Gas-filled swim bladderGills Gill slits but no gill cover Covered gill slitsReproduction Eggs fertilized in female's body. Eggs usually fertilized in the water.Skin Rough, sandpaper-like placoid scales Slippery, overlapping scalesSIZEA 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 SHAPESSharks 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 SHARKSThere 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.
妮裳风云
鲨鱼用英语：shark ，读音：英 [ʃɑːk] 美 [ʃɑːrk]n. 鲨鱼n. 贪婪的人；放高利贷的人；老手v. 诈取；诈骗词汇搭配1、bonito shark 灰鲭鲨2、thresher shark 长尾鲨3、blue shark 大青鲨4、whale shark 鲸鲨常见句型：1、The shark is dangerous to swimmers.鲨鱼对游泳的人来说很危险。2、He told me he once caught a shark, but I know he was swinging the lead.他告诉我有一回他捕到了一条鲨鱼，我知道他是在胡诌。3、They were killed by a man-eating shark.他们被一条吃人的鲨鱼所害。扩展资料：shark的同义词有：sharper、fraud , swindler1、sharper英 ['ʃɑːpə] 美 ['ʃɑrpɚ]释义：n. 骗子；赌棍；欺诈犯例句：Her old sharper of a father did it.她那骗子父亲干的好事。2、fraud英 [frɔːd]美 [frɔːd]n. 欺诈;骗子;伪劣品;冒牌货[例句]She had committed fraud, embezzlement and theft.她犯了诈骗、贪污和盗窃罪。3、swindler英 ['swɪndlə]美 ['swɪndlɚ]n. 骗子[例句]Never shall I trust that swindler again.我再也不会相信那个骗子了。
真理在朕
There are at least 350 species of shark ranging from the smallest, the pygmy ribbontail catshark (8 to 10 inches long) to the largest, the whale shark (upto 45 feet long) Sharks are equipped with a special set of sensors, arranged in clusters over their heads, that can pick up electromagnetic currents emitted from other animals. Sharks have bad eyesight, but these sensors help detect prey from 1 to 3 yards away. Sharks can also detect the electromagnetic fields of the Earth and may use this ability to guide them during migration. Sharks are often thought of as cold-blooded killers that prey on humans. However, only 32 species have been known to attack humans, and most attacks are accidents. Often, sharks inhabit the same shallow, warm-water areas as humans. The shark may mistake a person standing or floating in water for natural prey. The shark goes in for the kill but, after one taste, usually gives up the attack. Many shark attacks involve people trying to free sharks from fishing nets. Sharks also are territorial animals and may attack if they feel threatened. The chances of being attacked by a shark are very small, and the chances of dying from a shark attack have greatly decreased over the years. In fact, in the United States, a person is 30 times more likely to be killed by lightning than by a shark. Dog bites are 1,000 times more common than shark bites. Sharks are fished for their fins and cartilage. Shark-fin soup is a popular food in some areas. After the fin is cut off, the rest of the shark is discarded. Shark cartilage is a subject of much scientific study because medicine made from it may stop the growth of tumors. Shark cartilage is sold in pill form as an alternative medicine. Shark finning and fishing for cartilage have caused a decline in populations in some areas of the world. Sharks mature and reproduce slowly, so it is difficult for them to rebound from a decline.Great white shark: Best known from the movie Jaws, the great white is a large, heavy-bodied shark, about 20 feet long, with large bladelike teeth. Widely the most-feared of sharks, great white attacks are rare, and most scientists agree that its reputation is undeserved. Many scientists believe it is endangered due to sport fishing and shrinking food supplies.Whale shark: Reaching lengths of up to 50 feet, the whale shark is the largest fish on earth. This gentle giant has small teeth like whale baleen, through which it strains small fish and crustaceans.Tiger shark: The tiger shark is considered one of the most dangerous sharks. It is about 18 feet long and inhabits shallower water, often where people swim. The diet of tiger sharks varies widely and includes all types of sea life and even garbage. Blue shark : The graceful blue shark is well known to scuba divers and commercial fishers - they have been seen circling divers and have followed fishing boats for days, eating stray fish.Mako shark : Short-fin and long-fin makos are close cousins with the great white shark. They are very fast swimmers and can reach speeds of up to 60 miles per hour. Mako sharks can even leap out of the water.Hammerhead shark : Hammerheads are best known for their distinctive mallet-shaped heads and widely spaced eyes, which they swing back and forth while swimming to detect prey. They are the only species of shark known to travel in schools.Bull shark : The bull shark gets its name from its snout, which is wider than it is long. It is possibly more dangerous to humans than the great white shark because it lives in shallow, murky water in areas where people swim. The real shark attacks on which the movie and book Jaws were based were done by a bull shark.
谦谦妈妈2015
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
超级尺蠖爱和平
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：
