What Is A Shark?
All sharks belong to the class of fish called Chondrichthyes, which unlike bony fish have skeletons made of cartilage. Sharks do not have scales like bony fish but instead have rough skin. Their skin is covered with tiny sharp teeth called dermal denticles. These teeth can scrap the skin off your hand if you rub it the wrong way, which is from tail to head. When rubbed from head to tail sharks feel smooth (with the exception of a few species). The denticles are there to make the shark move silently, and protection. Another thing that separates sharks from bony fish is that their backbone extends into the upper lobe of the caudal fin. The shark also fertilizes internally, and has fewer young then bony fish. Reproduction will be in a different section.
Shark Anatomy (Internal)
internal skeleton of a shark is made of cartilage and connective tissue
making the shark very
largest organ in a shark is the liver. The shark lacks flotation bladders
and that is why most sharks will sink if they stop moving. The liver
contains an oil, called squaleen, which helps to float sharks. The sharks
stomach can be turned inside out if the shark swallows something it cannot
digest. Male sharks have a pair of claspers that are formed from the inner
pelvic fins. I will get into further detail on shark reproduction later.
The shark's brain is similar in weight to those of birds and mammals
making the shark the most intelligent of fish. Sharks can even be
Sharks come in many different sizes, and shapes. Most sharks are shaped like a torpedo, but not all. The angel shark is flat like their close relatives the rays. Thresher sharks have a very long tail, which makes up half its length. Frilled sharks are long and eel like. Not all sharks are huge like most people think. the smallest shark is the Pygmy Lanternshark (_Etmopterus perryi_) which is only 5 inches long. The whale shark however is 40 feet long. Most sharks have 5 gill slits, but not all. Sharks with more then 5 are considered ancient to some scientists.The shark is built like an air craft, and is perfectly built for the sea. The pectorial fins help the shark turn and steer, the tail is used for steering, moving, and speed control. Sharks that live in the open ocean have streamlined torpedo like bodies. All sharks have the same basic parts in the drawing below, though the Dogfish have no anal fin, and some benthic sharks have a sperical to help them stay still in water.
SIXTH SENSE: The shark has all the senses that we humans do but they also
have one we don't have. Tiny pores on the snout leads to jelly-filled sacs
known as ampullae of Lorenzini. This sense can detect very weak electrical
fields that can detect electrical "vibes" as weak half a
billionth of a volt. Struggling or scared animal creates a strong
electrical current, which flows through the water, and even though it gets
weaker as it travels away from the animal sharks can pick it up. Every
animal sends electrical "vibes". A shark can find animals under
the sand, and at night, and when at the last moment of attack when the
eyes are rolled back and it cannot see. In many cases when doing shark
research the shark would attack the boat and other objects instead of the
food offered. Humans used to
THE LATERAL LINE: The lateral line is another sense that we human do not have. The lateral line is a fluid filled canal that is lined with tiny hair like receptors that are attuned to vibrations made by prey. These lateral lines are located just under the skin on the shark's snout and along both sides of the body. These lines are also in bony fish. Fish (sharks included) can also use these lines to sense water currents and pressures and even sounds. Some say that the bumping behavior of sharks allows external taste receptors to see if the organism is edible (this may explain why sharks often bump objects).
SMELL: Unlike the nostrils of "higher" animals, sharks are not used for repertory functions. The shark can sense one molecule of blood in a million molecules of water. Each nostril is divided by a skin flap, which separates the water flowing in and out. As the fish swims water enters the nostrils and through the nasal capsule that contains lamellae. Lamellae increase the shark's sensitivity to odors. The olfactory bulb is close to the front of the brain.
HEARING: The shark has an excellent sense of hearing and can hear the low pulsing sounds made by animals swimming, splashing, and struggling. These sounds are too low for humans to hear, however sharks can hear them from a thousand miles away. Sharks do not have external ear flaps, but instead have ears inside their heads on both sides of the brain case. Each ear leads to a small pore on the sharks head. A shark's inner ear can also detect acceleration, and gravity.
SIGHT: It was
once thought that sharks had very bad eyesight, and were nearly blind. It
is know known that sharks have very good eyesight, some better then ours.
Like cats, a shark's eye contracts or expands to alter the size of the
pupil, according to how much light there is. In the back of the eye there
is a layer of cells known as the tapetum lucidum. The cells reflect light
back onto the retina. This is where images are focused, making good use of
light. Due to this a sharks can see in dim light, and the
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