8.Ampullae of Lorenzini
13.Caudal or Tail Fin
14.Second Dorsal Fin
15.First Dorsal Fin
All the creatures living under water have certain characteristics in common. They all need a way to get oxygen. They all need to reproduce to make sure their species continues. They all need to eat to live. But each species also has special features
which are unique.
Sharks have highly sensitive senses, a special liver which helps them to float, several rows of teeth, and eyes which aren't so different from yours. Like rays, shark skeletons are made of cartilage. The shape of a shark is specially designed to help it navigate long distances and maneuver around its prey with ease. Its several pairs of fins help it navigate through the water, kind of like our legs get us humans around, and our arms help us keep our balance.
A shark has several pairs of gills on either side of its head, unlike other fish who only have one gill on each side. You probably breathe through your nose and mouth, but a shark only uses its nostrils for smelling. When peo
ple don't want to be seen by their enemies they sometimes wear fatigue suits. Sharks are born with their own special colors to protect them from predators above and below them in the water.
The bones of a fish are made mostly of calcium, but a shark doesn't really have any bones. A shark skeleton is made of cartilage. Bony fish have a gas-filled swim bladder which enables them to float in the water, but sharks have no such bladder. Since cartilage is lighter than bone, it helps to keep a shark from just sinking to the bottom of the ocean. A shark doesn't have as many moveable parts as a bony fish, which in some ways makes a shark a little more clumsy. But cartilage is more flexible than bone, so a shark can turn around in a smaller space than a bony fish. Sharks keep growing cartilage as long as they live, and have extra mineral deposits in their jaws where they need extra strength, (the better to bite you with).
When engineers came up with the shape of a DC-9 airplane, they were thinking about the fastest way to travel using the least amount of energy. If you compare the DC-9 to a shark, you will see that their shapes are amazingly similar. They both have round bodies tapering off at both ends. This shape allows the plane to glide through the air, and the shark to glide through the water, without using up all their fuel before they get where they want to go.
Sharks are generally a dark color on top, which is called their dorsal side, and a light color on the bottom, which is called their ventral side. Predators looking down might not see the dark top of the countershaded shark, because it blends in with the dark ocean depths. But if a predator looks up from below, the light bottom of the shark blends in with the lighter surface of the sea where the sun shines. Either way, the shark manages very well to blend in with its environment and avoid being seen when it doesn't want to be seen.
Sharks do have noses, but they only use them for smelling, not for breathing. You'll find their pair of nostrils on the underside of their snouts. Some species, like the Nurse Shark, even have some extra smellers called nasal barbels, which stick out near the nostrils and mouth.
These are electroreceptive organs. The ampullae are jelly-filled pores shaped like ampullae (clay jars used by the Romans and others to store grain, oil, and wine). The function of these organs was not discovered until fairly recently. They are electr ical field sensing devices, and as everything living produces an electrical field, the shark can detect the presence of another living creature even if all its other senses were deactivated. The ampullae are distributed around the head, and the external openings and are large enough to be seen with the naked eye.
In an experiment, a group of sharks and rays were trained to eat in an area directly over a pair of electrodes buried in the sand bottom. When the sharks were fed fish, the current was turned on and emitted four-tenths of a microvolt. Then when the food was withheld, but the current turned on, the sharks and rays swarmed about the electrodes, uncovering them and snapping at them Thus it was shown that the animals could sense minute charges of electricity and could trace it to its source.
Sharks, as all fish, use their body and tail in a side to side motion to move through the water. Shark fins are rigid not flexible, and are supported by rods made of cartilage. Sharks have five different kinds of fins.
Sharks have five to seven gill slits on each side of their head, unlike bony fish which have one gill on each side. As water passes over their gills, oxygen is absorbed by the blood in the gills and transported from there to the rest of the body.
Some sharks have small openings called spiracles behind their eyes, at the top of the head. Spiracles are sort of like baby gill slits. The more active, fast swimming sharks seem to have outgrown the need for these spiracles, and only have very t iny ones or don't have them at all.