Sharks have body parts that are common to all species, but certain species have body parts that have evolved to fulfill certain needs for that particular species. Because sharks do not have a swim bladder like most other fish, their liver has evolved to help them float.
Sharks do not have bones. Instead, their skeleton is composed entirely of cartilage, which is lighter than bone and contributes to their remarkable speed.
Fins are thin projections on a shark's body that fulfill different functions such as propulsion, steering and balance. The anal fin, which not all sharks have, also aids in steering their body through the water.
Sharks are unique among underwater creatures in that they have five to seven pairs of gills on either side of the head, instead of a single pair, which they use to remove oxygen from the water.
Sharks have a double row of parallel teeth that continue to be replaced as they fall out throughout their life. Different species' teeth have evolved for their special feeding needs, such as serrated teeth for tearing flesh, conical teeth that crush through the shells of lobster, crab, etc, and thin pointed teeth to grab and hold prey.
A shark's skin is composed of rough scales called dermal denticles, which are small rough projections that form a protective barrier and help in swimming.