The animal on the cover of Web Security,Privacy &Commerce,Second Edition is a whale shark.Sharks have lived on the Earth for over 300 million years,and populate all the oceans of the world (as well as some freshwater lakes and rivers).They are related to skates and rays,differing from ordinary bony fish in having a cartilaginous skeleton that makes their bodies unusually flexible.Unlike bony fish,sharks give birth to live young,in small litters.
A common misconception about sharks is that they need to keep swimming at all times.While they do need to move their fins constantly in order to stay afloat,many species of sharks like to rest on the bottom of the ocean floor.
Sharks make excellent predators because of their well-developed sensory system (not to mention their big,sharp teeth).They have excellent eyesight and an unusually keen sense of smell;they are known to be able to locate prey from a single drop of blood.
Sharks can also sense electrical currents in the water indicating the presence of other fish.They retain several rows of teeth,which roll outward to replace those that are lost.
The whale shark,on the other hand,is a kinder,gentler shark.Whale sharks (Rhinocodon typus )have a large flat head,a wide mouth,and tiny teeth.As a filter feeder,they feed primarily on plankton and small fish.They have distinctive spotted markings on their fins and dorsal sides.Whale sharks are so named because of their size:they may weigh more than 18 metric tons and measure up to 60 feet long.They are the largest species of fish alive today.
Whale sharks live in tropical and temperate seas.They pose little or no risk to humans.In fact,whale sharks are considered a particular treat to divers,since they are impressive in size but are slow-moving and not aggressive.