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Shark – a ghost or an elephant shark

How many unusual and previously unknown for me personally exists even in such a popular topic as SHARKS. Well, it would seem, sharks and sharks. There is white, there is a reef, tiger, whale – who does not know about them. But in fact there are many sharks about which many really do not know. Well, for example, to vskidku: AKULA – Goblin , but the Big-footed shark and even there are Wobegongs or a shark-rug, not to mention the relict Plaktosnuyu shark

But today I will tell you about another shark, which I learned about only now. Yes, that’s about the one on the photo.

So …


Picture 2.

The elephant shark-phantom (Callorhinchus milii) (or the Australian callorhynchus) has a unique appearance – nature awarded it with such an outstanding “nose” that it would not be easy to confuse this fish with any other marine creature. Spectacular elephant shark (Elephant shark), also called elephant fish and Australian shark-ghost, belongs to the chimera group and is closely related to other types of sharks and seahorses.

A photo 3.

As a habitat, the unusual fish chose the waters of the South Australian and New Zealand coasts. It rarely catches the eye of people, because it prefers solid depths – 200-500 meters. It is the ocean floor that serves as a shelter and a table for this extravagant representative of the underwater world.

A photo 4.

Melbourne Aquarium, Victoria, Australia. Rare elephant shark hatchling in the Melbourne Aquarium.

The length of the elephant shark, or shark-ghost is from 70 to 120 cm. From the bottom, her body is silvery-gray in color, reminiscent of the color of the foil, and the back with fins is covered with brown spots and divorces, which serves as a successful masking for her.

The amazing organ for which the elephant shark and got its name, is a growth on its chin and strangely reminiscent of the trunk. Nature does not give out gifts just like that – especially not so trivial: it is obvious that the trunk of this fish has its purpose. And, as it turns out, very important! After all, he is directly involved in the search for mollusks, crustaceans and larvae, the favorite food of elephant sharks, that live on the ocean floor.

Picture 5.

Radiating a tender silvery glow, the shark ghost floats unhurriedly over the bottom, leading the trunk from side to side, deftly using it and as a locator, and as a shovel. The picture of a shark poop working on the extraction of food is reminiscent of a sketch from everyday life of an underwater treasure hunter, which, with the help of special equipment, thoroughly examines the bottom.

A photo 6.

But how does the elephant shark-ghost come out of the situation in conditions of zero visibility – at night or in bad weather? After all, hunger is not an aunt – it can be caught in muddy water, and in pitch darkness.

It turns out that even in conditions of increased complexity of a shark, a ghost does not face death from exhaustion, because the most outstanding organ replaces his vision. And in the search for food, not only the shark’s trunk is involved: on the equal rights with it in the process of obtaining larvae and other invertebrates, buried in the ground, the tail of the fish also participates, which in usual conditions is used as a rudder. On the multifunctional tail shelter set of cells that can produce electrical pulses with a frequency of 80 times per second.

A photo 7.

The trunk of the phantom sharks, in turn, is equipped with other cells sensitive to changes in the electric field. Catching the chin in the field of distortion, it receives reliable information about the features of the surrounding landscape. Thus, elephant shark-ghost is a complex mechanism for the effective production of feed, consisting of a flashlight-tail and a sensitive chin chamber.

By the way, the picture that appears in the head of an elephant shark differs in detailed drawing of nuances and even with the presence of color, so much more like a landscape than a dry drawing. Such a capacity for night vision allows her to easily find food at the bottom even in darkness. The biologists inexhaustible for the invention decided to complicate the task sharply, digging the larvae deep into the sand – but in this case, she brilliantly coped with the work.

If the elephant shark chooses places for living deeper, then with the approach of spring it migrates to the coastal bays, in shallow water for mating and laying eggs. Eggs of the elephant shark are enclosed within yellowish-brown horny capsules about 25 cm long.

After about 8 months, fry hatch out of the eggs laid in the coastal sand – no more than 10-15 cm in size. Elephant sharks grow extremely slowly – they need at least 5 years to reach maturity.

Despite the fact that in some areas of New Zealand and South Australia, where the elephant shark lives, it is an object of fishing (its white fillet is actively used in local cooking), the disappearance does not threaten it.

Perhaps the reason is that on the South Australian coast there is almost a 5-kilometer zone where fishing is strictly forbidden and where all the representatives of the numerous fish kingdom can freely breed and multiply.

A research team from the Institute of Molecular and Cellular Biology, Singapore ( Institute of Molecular and Cell Biology in Singapore ), operating headed Birappoy Venkatesh ( Byrappa Venkatesh ), studied gene sequence ivory shark species Callorhinchus milii , also known as the Australian shark ghost.

The study should help shed light on the evolution of vertebrates and present scientists with the first complete analysis of the genome of cartilaginous fish . This class includes sharks, skates and skates. Together with bony fishes , birds, reptiles, amphibians and mammals, they form a branch of the jaw vertebrates.

The genome of the elephant shark is relatively small: it consists of slightly less than one billion base pairs of DNA (for comparison, in the human body, three billion base pairs). However, this sequence demonstrated to scientists intriguing details. For example, the elephant shark genes secrete complex proteins of phosphoproteins, so their cartilage never turns into bones (as occurs in other jaw vertebrates).

Also, these animals lack the genes of several key cells of the innate immune system and protein receptors in the adaptive immune system, the so-called “immune memory”, which is able to provide protection from a variety of diseases. This discovery suggests that the adaptive immune system developed in jaw vertebrates gradually, over time.

In the immune system of the elephant shark, there are T cells capable of destroying cells infected with viruses, but they do not have an auxiliary T-cell that regulates the general immune response to infection.

One of the most notable features of the elephant shark genome is its incredibly slow evolutionary pace – at the moment the animal looks almost the same as 420 million years ago. In fact, these creatures have changed for hundreds of millions of years even less than the “living fossils” of the coelacanths . This slow pace of evolution is explained by introns in the genome of C. milii . In vertebrates, these introns are contained in thousands of DNA records and include their own splicing instructions . Most invertebrate creatures (eg, shells) the evolution of introns is much faster. Also, scientists noted that the possibility for mutation accumulates in the genomes of invertebrates: thus, the development of “spineless” occurs more quickly.

According to researchers, the elephant shark genome is closest to the DNA of the first jaw vertebrate, who lived on the planet more than 450 million years ago and gave rise to many modern animals, including humans. The elephant shark is important for understanding the development and evolution of this distant ancestor, as well as all modern species.

The work of scientists is described in detail in an article published in the journal Nature .

But that’s not all. It turns out that the Elephant Shark is the only shark that has a COLOR VISION!

The eyes of the sharks make a strange impression: they are dull and inactive, they are at the same time cold and sensible. The unblinking look of the shark inspires primitive horror and paralyzes the will. Previously believed that sharks were blind, but this is not entirely true.

The eye of a shark has a peculiar structure: on its back wall there is a retina consisting of only rod-cells, perceiving movement and contrast of light and dark.

The eye of the shark does not contain photoreceptors-cones in the retina, so it is not able to distinguish colors and is ill-suited to fix fast movements. In part, this is compensated by a significant number of rods – cells that perceive weak light. In addition, behind the retina, many species of sharks have a glossy silver membrane (tapetum lucidum), which reflects the light passed by the photoreceptor cells back to them and thus increases the light sensitivity of the shark’s eye, which especially affects the depth and the turbid water.

The smell of sharks is so perfect that a few drops of blood in the water excite them a few kilometers away. Feeling the prey, the excited shark begins to move in zigzags – alternately turns the right and left nostrils to determine the direction of the smell and localize its source. Thirty meters before him, sharks are beginning to be guided by sight. If the shark is stuck in the nostrils, it will float past the prey, even if it is in front of her eyes.

Sight in sharks, black and white, perceiving only the tonality of the color, if you want to attract the attention of sharks, dress in white or black, take a metal canister or something shiny. And then the attention of sharks to you is ensured.

The only shark with color vision is the elephant shark (callorhinchus milii).

Elephant shark – belongs to the class of cartilaginous fishes. This species, one of the oldest representatives of this systematic group, appeared about 450 million years ago. Elephant sharks live in continental shelf areas off the coast of Australia and New Zealand at a depth of 200 to 500 m. Adult individuals at the age of three to four years migrate to shallow waters in bays and estuaries. There at a depth of 6-30 m the female lays two fertilized eggs each week for two to three months. Six to eight months later, small sharks appear, which leave the warm shallows and go to the depths. Therefore, during life elephant sharks encounter different habitats – first with full colors of light, and then with a darkened and monotonous. Scientists believe,

The retina contains two types of photoreceptors – rods and cones. The sticks contain only one light-sensitive pigment, so they do not participate in color vision. The second type of photoreceptors is cones. They already contain three types of photosensitive pigments. This feature also enables the eye to perceive colors. Each type is responsible for color perception in a certain part of the spectrum – shortwave, medium wave and long wave. The S-type cones are sensitive to the short-wave part of the spectrum (in the violet-blue region). M-type cones – to the medium-wavelength green-yellow part of the spectrum. L-type cones – to the long-wave part of the spectrum (in the yellow-red region).

More recently, the genome of elephant sharks has been completely deciphered thanks to a special project, in which Professor Hunt also took part. And, according to him, this is the first representative of the class of cartilaginous fish, the genome of which is completely deciphered.

Based on the data obtained, the scientists were able to isolate genes encoding various photosensitive pigments of rods and cones:

· Rh 1 gene, which encodes the rod pigment;

· Three genes encoding cones sensitive to the middle part of the spectrum (yellow-green);

· Lws 1 and Lws 2 genes encoding pigments sensitive to the long part of the spectrum (yellow-red).

According to Professor Hunt, it’s amazing, but pigments sensitive to the short-wave part of the spectrum (violet-blue), the elephant shark was not found. But in his desire to perceive colors, this species found a way out. According to Professor Hunt, these sharks have invented a unique model of color perception, when the long-wave receptor perceives and short waves.

So it’s safe to say that elephant sharks have trichromatic vision and perceive light in all areas of the spectrum.

Sources

http://www.akulizm.ru/neobychnye-vidy-akul/slonovaya-akula-prizrak.html

http://www.vesti.ru/doc.html?id=1191827&cid=2161

http://www.zooeco.com/0rib0-rib556-14.html

http://www.infox.ru/science/animal/2009/03/18/Slonovyyye_akulyy_ob.phtml

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