ABOUT SHARK!

 What is Shark?

Sharks are a group of elasmobranch fish characterized by a cartilaginous skeleton, five to seven gill slits on the sides of the head, and pectoral fins that are not fused to the head. Modern sharks are classified within the clade Selachimorpha(or Selachii) and are the sister group to the rays. However, the term "shark" has also been used for extinct members of the subclass Elasmobranchii outside the Selachimorpha, such as Cladoselache and Xenacanthus, as well as other Chondrichthyes such as the holocephalid eugenedontidans.

Under this broader definition, the earliest known sharks date back to more than 420 million years ago. Acanthodians are often referred to as "spiny sharks"; though they are not part of Chondrichthyes proper, they are a paraphyletic assemblage leading to cartilaginous fish as a whole. Since then, sharks have diversified into over 500 species. They range in size from the small dwarf lanternshark (Etmopterus perryi), a deep sea species of only 17 centimetres (6.7 in) in length, to the whale shark (Rhincodon typus), the largest fish in the world, which reaches approximately 12 metres (40 ft) in length. Sharks are found in all seas and are common to depths of 2,000 metres (6,600 ft). They generally do not live in freshwater although there are a few known exceptions, such as the bull shark and the river shark, which can survive and be found in both seawater and freshwater. Sharks have a covering of dermal denticles that protects their skin from damage and parasites in addition to improving their fluid dynamics. They have numerous sets of replaceable teeth.

Well-known species such as the great white shark, tiger shark, blue shark, mako shark, thresher shark, and hammerhead shark are apex predators—organisms at the top of their underwater food chain. Many shark populations are threatened by human activities.

Every shark species has its own expected life span and so it is wrong to set an average for sharks as a whole. However, very broadly speaking, we can say that most sharks live for between 20 and 40 years. The Spiny Dogfish lives for over a century, and Whale Sharks are expected to be similar.

Unlike most other animals, sharks do not care for their young. As soon as pups are born into the water, they swim away and care for themselves. Some sharks give birth to litters of up to 100 pups at a time, while many species may have as few as two or three. In almost all cases, all of the pups are healthy and well-developed. This is in stark contrast to many other animals (such as several fish species and some turtles), which give birth to large numbers of ill-developed young (in effect, producing quantity over quality).

Mating amongst sharks is somewhat elusive, rarely seen by researchers and scientists. Fertilisation of the female egg occurs internally. The male’s pelvic fin (the fin on the underside of the body, close to the tail) has evolved into claspers, a pair of organs that can best be compared to a penis in mammal species.

Once fertilised, sharks will carry their young in one of three ways:

   

• Oviparity – Some sharks lay eggs, protected within a leathery egg case.
• Viviparity – This term is used to describe the sharks that have a placenta from which to feed and sustain their young inside. The young are born alive and at full term.
• Ovoviviparity – The majority of sharks lay eggs inside their body. These hatch and the young remain inside for some time. Eventually, they are born alive and fully developed. Some shark species display a form of cannibalism in that the first pup to hatch eats the other eggs or pups while still inside its mother. This is called oophagy.

The gestation period for ovoviviparous species is not known for sure. However, it is thought to be anywhere from several months to over two years.

There have also been isolated cases of asexual reproduction, meaning that the female has managed to conceive and birth pups without any input from a male. The cases have all been observed in sharks in captivity. The incidence of asexual reproduction in the wild remains unknown and is believed to be a last resort method of reproduction in the absence of males.


Sharks owe much of their effectiveness as predators to their good sensory system. Their senses are not integrated but depend on each other to provide reliable acuity. Sharks can smell thousands of times better than any human being and can detect at long distances chemicals in the water.

1. Vision
Not all sharks have the same vision capability. Some are more sensitive to light while others have poor sight. Most have a relatively broad field of vision, as in the case of the hammerhead shark (believed to be able to see 360 °).

2. Smell
Sharks have nostrils that they only use to smell. When they swim, water flows through the nostrils, is introduced into the nasal duct and moves the last folds of the skin that has sensory cells. Some sharks, such as the lemon shark (Negaprion brevirostris), can detect a small amount of blood in the water.

The sense of smell is directional, this means that if the aroma comes from the left side of the shark, the shark first perceives it precisely in the left fossa rather than the right and can detect the location of the source of the smelling.

It is necessary to emphasize that they are very sensitive to odors and can differentiate a prey from another shark and even from a predator and respond in a decisive way to the smell produced by a wounded or fearful prey.

3. Ear
Their sense of hearing is also sharp although they do not have ears, but small openings in the sides of the head and inner ears similar to those of some mammals.

Under the sea, sharks have the ability to hear sounds in a range wider than the human ear and detect the sound source from many kilometers away. This capability is especially useful when hunting because if they listen to the low-frequency sounds produced by injured animals, they do not hesitate to follow the source until they reach the prey and feed on it.

Question  about SHARK !

1. When were sharks first discovered?
a. 5 million years ago
b. 124 million years ago
c. 420 million years ago
d. 1o million years ago 


2. What's the largest shark species?
a. Blue shark
b. Whale shark
c. Jumbo shark
d. Tiger shark

3. Is a shark a mammal?
a. No
b. Yes
c. Both
d. Not both 

4. What's the smallest shark species?
a. Tiger shark 
b. Whales shark
c. Mikro shark
d. Dogfish shark 

5. What's the name for sharks that live in the deepest parts of the ocean?
a. Benthic shark
b. Sleepy shark 
c. Tiger shark
d. Whale shark 

6. The World's fastest shark?
a. Runner shark
b. Cheetah shark
c. Mako shark
d. Miko shark 

7.The slowest shark?
a. Snaily shark
b. Greenland shark
c. Arktik shark
d. Dogfish shark 

8. Can sharks hear? 
a. No
b. Yes
c. Both
d. Not both

9. What are some of the most endangered shark species?
a. Tiger shark
b. Whale shark
c. Hammer-head shark
d. Sawfish shark 

10. Are there any sharks that glow in the dark?
 a. No
b. Yes
c. Both
d. Not both



source : - www.sharksinfo.com/life-cycle.html
-https://www.google.com/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&ved=0ahUKEwiNvpC7neDYAhWFvI8KHeDQCqQQjRwIBw&url=https%3A%2F%2Fsites.google.com%2Fsite%2Fgreatwhitesharkho2015%2Flife-cycle&psig=AOvVaw34fcYZYh8lYnRbKSmK34Ax&ust=1516320835401515
- http://www.sharks-world.com/shark_senses/
- https://www.google.com/amp/welovesharks.club/30-awesome-shark-questions-answered/amp/