To say who is the killer of the deep sea, the first thing that many people think of may be sharks. If nothing else, the movie "Jaws" and "Megalodon" have left no less psychological shadows on people, and the blood basin mouth and huge size are enough for you to be stunned for half a day.
Come, come to my mouth
Image source: Movie "Jaws"
Already scared to swim
Image source: The movie "Megalodon"
Sharks are so powerful that they can't do without their "top match". From the skin to the internal organs, from the visual and auditory senses to the "sixth sense", each shark is fully armed and waiting for an opportunity to launch a deadly attack.
Sharks have their own mysterious aura, accompanied by a lot of strange rumors, such as you must have heard of "sharks change tens of thousands of teeth in their lives" and "sharks can smell a drop of blood a few kilometers away", right? Today let's take a look at whether the shark is so magical.
1 Sharks change tens of thousands of teeth in their lifetime?
Answer
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Shark teeth fall out easily and are replaced regularly. Most sharks have only the outermost row of teeth in working condition, and the rear teeth are substitutes, constantly rotating outward like a conveyor belt.
Shark teeth
Image source: qz.com
Shark teeth are not one row, but N rows (ranging from 3 to 6 rows to more than 300 rows (whale sharks)), hundreds to thousands. Different species of sharks, with teeth of different shapes and sizes, are suitable for hunting different prey.
Take a look at the whale shark's big mouth:
Dentist: Oh, yes, you have to open your mouth to extract your teeth
Image source: travel4wildlife.com
If you can't see its teeth clearly, I'll zoom in on it and notice your lower lip:
Whale sharks have dense teeth
Image source: travel4wildlife.com
If you still can't see clearly, just look at the whale shark teeth close-up below.
Whale sharks have dense teeth
Image credit: wiki
This dense and neat tooth, I am afraid that even the dentist will have to call "good guy"! Come, next, please dentist readers to post their thoughts in the comments section.
2 Sharks drown if they don't swim?
Answer
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In fact, only a few pelagic sharks, such as man-eating sharks and barramundi sharks, are like this: they only "breathe forward" and must swim up and let the sea water rush into their mouths to obtain oxygen.
Gill clefts are the respiratory organs of sharks, striped, with a total of 5 pairs (6 to 7 pairs of six-gill sharks, 6 pairs of some members of the sawshark order). Image source: science.org
Most sharks will also "suck and breathe", it doesn't matter if the body does not move, the aquarium can often see sharks "lying flat" at the bottom of the tank.
Right: Tired and don't want to struggle anymore
Image source network
3 Will sharks sink without swimming?
Answer
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Although there is buoyancy provided by the liver and cartilage, the shark has to hover in the water and still have to swing its tail fin to remain unsinkable.
The liver is the largest organ in the shark's body and can weigh more than 20% of the body weight. Shark liver is rich in low-density oils, in addition to storing nutrients, but also provide buoyancy - sharks do not have swim maws, so they have to rely on liver to "work part-time".
Sharks have only cartilage all over their bodies, but key bones such as skull, jawbone and spine are partially calcified and have a certain hardness. Cartilage also loses weight and increases body buoyancy.
The body and skeleton of the porbeagle shark
See watermark for image source
Let's talk about the shark's fins and skin. Sharks generally have 8 fins, and the inside is supported by a strip of filamentous cartilage, so the "shark fin" is cooked like a vermicelli (not to make you eat shark fin soup).
The skin of the shark is not as smooth as it seems, it looks like a whole shark skin, and the surface is countless small, dense "shield scales". Shield scales are different from the fish scales we are familiar with (the "bone scales" of teleost fish) and have an internal structure similar to teeth. The surface of shark skin is rough and sharp, like sandpaper.
Shark's shield scales
Image source: moviecultists.com
When it comes to sandpaper, have you thought of anything? Isn't that what we said two days ago about the skin texture of the consumed fish?
4 Are sharks myopic + colorblind?
Answer
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Not entirely. Some pelagic sharks have not bad vision and may even have abundant color vision.
Sharks have a reflective film (choroidal layer) behind their retina, which reflects faint light onto the retina and helps them see things in the dim deep and muddy waters.
Sharks have no outer ear, only the inner ear. Because sound waves travel more than 4 times faster in water than in air, sharks, like most aquatic animals, have a keen sense of hearing and can lock on to prey more than 200 meters away.
In addition to hearing and vision, sharks have a secret weapon – the side line. Like bony fish, sharks have a lateral line on each side of their bodies. There are many sensitive nerve cells on the lateral line, which can accurately sense the weak changes in water pressure caused by foreign interference and prey swimming.
Great blue shark
Image source: fisheriesireland.ie
5 Can a shark smell a drop of blood from a few kilometers away?
Answer
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Experiments with several sharks have shown that they can sense 25 to 10 billion parts of blood, which is equivalent to smelling a drop of blood in a swimming pool.
hiss......
Image source: The movie "Shark Sea"
Sharks breathe with gills, noses are only used to smell, and they are very sensitive. The 1-meter-long baby shark has a surface area of about 5,000 square centimeters in the nasal cavity, and a large number of olfactory cells are distributed, and the olfactory lobes responsible for smell in the brain are also developed.
A powerful skin sensory vessel called a Loren-style urn, also translated as The Loren's ampb, is the source of the shark's "sixth sense". It is mainly distributed in the snout, and from the surface of the body, there are many small holes, each of which is connected to the subcutaneous tubule. The inside of the tubule is filled with a lens of colloid and is connected to the nerves.
Small holes in the body of the tiger shark
Image source: fa.wikipedia.org
Loren-style urn
Image source: Wikipedia
It took scientists more than 300 years to figure out the role of the Loren-style urn, mainly to perceive electromagnetic waves — sharks can accurately detect the biological electric field of their prey through it, and even use the Earth's magnetic field to "navigate" themselves.
The nervous system that connects the Loren-style urn
Haven't you seen these things yet? Don't worry, the theme of our new issue in May is sharks. Sharks are an ancient family with more than 300 million years of history and more than 500 extant species. Most of them are indeed efficient predators, but they are not blindly murderous, and most of them are not a threat to humanity.
In this issue of the magazine, not only the global sharks are taken stock, but also the whale sharks will be taken with them. In addition to sharks, there are also cute Andlovable Malay tapirs, "Coin Legend" knife coins, delicious cherries and tea and rice. In short, buy to see!
Old rules
Today we will draw 5 friends from the comments section
One person gives one may magazine
Please speak enthusiastically
Written by | Zi Fan
Drawing | Zheng Qiuyang
WeChat Editor | What a cool