The most feared creature of the sea is the shark. The shark has been branded a man eater for years. Contrary to popular belief, most sharks are not aggressive towards humans. Unprovoked attacks are rare. Sharks usually retreat when confronted unless they are threatened. Only about twenty species of shark are known to attack humans. These species are usually attracted by blood or by any unusual movement in the water. The typical shark body is torpedo-shaped. The upper half of the tail fin is longer than the lower half. Both male and female sharks have pectoral fins.

In male sharks, the pectoral fins have been modified into claspers. Claspers are a pair of sexual organs which contains sperm. Pectoral fins are located on the bottom of the shark towards the beginning of the tail. Most sharks are black, brown, or gray. They usually have lighter undersides. This allows for camouflage. The ocean floor is of a dark color because of lack of light. The shark has a dark upper body. When you look down on a shark, you see the sharks dark upper body against the dark ocean floor. This makes the shark difficult to see.

Just the opposite, the shark has a light colored underside. When looking up at a shark, you will see the sharks light underside against the light from the sky. Sharks have many features that set them apart from other fish. For example, the skeleton lacks bone. The sharks skeleton is made up of cartilage. The skin is embedded with placoid scales. Placoid scales are horny structures that unlike the scales of most fish, do not overlap. Each scale bears a tiny toothlike projection called a denticle. If you were to stroke the shark from head to tail with your hand, you would not be harmed.

The denticles would cut your hand if you stroked the shark from tail to head. Like other fish, sharks breathe through gills. Sharks however, have five to seven pairs of gills with a corresponding number of gill slit openings at the sides of their head. Most other fish have only four pairs of gills. Most sharks are cold-blooded. Sharks have numerous rows of teeth and produce new teeth throughout their lifetime. Teeth of the outer row will periodically break off or wear down. When this happens, the next row advance in position to take their place.

Most sharks are powerful swimmers and chase their prey. Most sharks eat fish, mollusks, crustaceans, and seals. Sharks have sensitive pores that are called Ampullae of Lorenzini. Located on the chin and nose, these sensory organs are used to detect weak electric currents in the water. This helps the shark locate prey. Sharks reproduce by sperm and eggs. A few species are viviparous-the females give birth to live young. Some are oviparous-the females expel the fertilized eggs. The eggs are contained in leathery sacks. These sacks are often called mermaid's purses.

Mermaid purses are sometimes found on the seashore. Most species are ovoviviparous. This is when the female retains the fertilized eggs within her body until birth. Remember that next time you see a shark; they are not necessarily the man eating monsters they have been made out to be.