Shark Anatomy

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)

SKELETON: The internal skeleton of a shark is made of cartilage and connective tissue making the shark very
flexible and light. The shark has no rib cage, so when it is on land its own weight can literally crush its body.The shortfin mako shark is one of the fastest fish in the world along with tuna, and the sailfish. Because of the sharks fins it cannot swim backwards and has to fall away from objects. The only things that fossilize on a shark are teeth vertebrate, dermal denticles, and sometimes cartilage and even soft tissue such as muscle blocks and kidney tubules. You can tell a lot about a shark from its teeth. The teeth very according to the sharks diet. Tiger sharks teeth are used for sheering, and tearing, the port jackson shark has teeth used to crush shell fish, the wobbagong shark has teeth used to grasp prey, and the greenland shark has teeth so sharp that they were once used to cut hair by Eskimos. Sharks have a bite strength of 25,000 pounds per square inch, not much different then a humans.

ORGANS: The 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
trained. The olfactory bulb is close to the front part of the brain.

Anatomy (External)

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.

Shark Senses

THE SHARK'S 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
think that the shark was just a stupid, crazy eating machine that went after anything. It turns out however that the shark when coming for the prey would roll it's eyes back and have the ampullae of Loranzini direct it to the prey. The boat gives out very strong electrical "vibes" which confuse the shark and direct it to the boats direction, and since the shark cannot see at the moment it would not know the boat is not the prey. Hammerhead sharks have a large number of ampullae of Lorenzini on their heads. Hammerheads use their heads like mine sweepers to find stingrays, and other prey in the sand. Large number of hammerheads can be found near underwater volcanoes which attract them from miles away with their electrical fields. The rare and strange goblin shark has a strange snout hanging over is head which may be used the same way as a hammerheads head and help it hunt in the deep dark water it lives in. Goblin shark teeth have been found in underwater electrical cables.

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
eye "glows" like a cats when light is shined on them. With pigment layers a shark can protect it's eyes on sunny days. The shark's eyes also have cells called rods, and cones. The rods work in dim light and are sensitive to changes in light. The cones may allow sharks to see color. We humans have rods, and cones. Fish lack eyelids because they don't need to blink and clean their eyes due to their watery environment. During attack some sharks use their nictitating membranes (translucent eyelids) to protect them from the thrashing animal. Sharks that have no nictitating membranes, like the great white for example roll their eyes into the back to their heads. The size, shape, and overall look of a shark's eye depends on their environment. Deepwater sharks have large eyes to take in more light, while smaller eyes are on sharks that live closer to the surface. It was once thought that great white attacks on surface were cases of mistaken identity, but researchers now know that this theory is not likely for a few reasons. Reason one is because white sharks have excellent vision and can probably tell the difference between a human on a surfboard, and a seal. The second reason is this; when a white shark attacks a seal it makes one huge bite, and kills the seal on the spot. When humans are attacked the shark usually takes one small bite and swims off. If the shark thought we were seals then it would do to us what it doses to the seals.

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