What Is a Shark?
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What is a shark? Well, there are many different ways to describe a shark. Many people describe sharks as "Killers", and "Vicious Beasts", but is that really true? Sharks are predatory cartilaginous fish. "Cartilaginous" means they have no bones. They have a much more stretchy substance called cartilage. This allows sharks to twist and turn in the ocean to hunt for food. On the left is a Great White Shark, probably one of the most famous sharks since the 1975 movie JAWS. Below is another well-known species of shark. One of the more than 5 varieties of its species, it's the Scalloped Hammerhead Shark. Although, back to what sharks really are.
How Sharks are Special
Sharks are very special fishes. Unlike other bony fishes, sharks must swim to survive. They do not have an airbladder. This is a picture of what an airbladder is. It's the white sac in the picture.
Shark Fins
Shark Fins are very special, too. The side fins are called the pectoral fins. These and the top fin, called the dorsal, prevent the shark from rolling over. The second bottom pair of fins are called the anals. They are located behind the pectoral and dorsal. Some species of sharks have 2 sets of anal fins, and often, behind the dorsal, you can find a much smaller second dorsal fin. Although, probably the most important fins are the caudal fin in the back. It provides lift for the shark, and is located on the tail at the very end of the shark. That's what pushes the shark forward by moving side to side.
Denticles
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Denticles are something else very extraordinary to sharks. They are hard scales that are like being covered in teeth. If you rub from snout to tail, a shark is very smooth. You can feel the denticles. However, they are extremely sharp. If you rub from tail to snout, the denticles will be rubbed against and you will be seriously cut open.
Lateral line
Sharks still have many extraordinary things in their anatomy. They have sensory organs in their body that are called a lateral line. This lateral line helps them tune into the electromagnetic impulses of living things in the water. When a fish in distress is writhing and wriggling in the water, it gives of electromagnetic impulses which sharks can pick up using their lateral line. The Ampullae of Lorenzini help with this. These are electroreceptors found on the snout of the shark.
Teeth
Sharks have many different kinds of teeth. The largest sharks will go through thousands of teeth in their lifetime. There are jagged teeth, like the Mako's and Sand Tiger's teeth, and then there are serrated edge teeth, like those of tiger sharks and great whites. Sharks are known to have many rows of teeth in one mouth, and when one falls out, the next day, it is replaced. It's as if the teeth are on a conveyor belt. However, there was one tooth that topped them all! The tooth of an ancient shark named Megalodon. It was actually just a goliath great white. The size of a semi! It grew to 50 ft. and higher!
Smell
Sharks have probably the most keen sense of smell of any animal. Three quarters of their brain are dedicated to smell. They can actually smell one drop of blood in an Olympic-size swimming pool!