Ken Schultz's Field Guide to Saltwater Fish - Macaw Pets store

Sharks (continued)
The upper and lower teeth of a mako
shark
194 Sharks
area of the intestine for more efficient absorption of nutrients.
Sharks are opportunistic feeders and will often eat
whatever is available.
Teeth. Shark teeth come in as many shapes and sizes as
sharks do. They also say something about the shark’s diet.
Some sharks are specialized predators; their
teeth are adapted for efficient capture of
their preferred prey. Others eat whatever is
available, and their teeth are amply suited for
many types of food. The great white uses its
triangular, serrated, bladelike teeth for grabbing
and biting off chunks of large fish and
marine mammals. At the other end of the
spectrum, the smooth dogfish uses its flat
teeth for crushing the shells of mollusks and
crustaceans. Others, like the mako or the
sand tiger, have narrow, pointed teeth for
impaling and holding onto prey small
enough to swallow whole.
Skin. Sharks have placoid scales, or denticles, which are
tiny, bony projections implanted in the shark’s skin. They
come in many shapes and sizes but usually completely
cover the shark’s skin like a coat of armor. Their main functions
are protection and reducing drag as the shark’s body
slices through the water. Denticles give the shark’s hide a
rough texture like sandpaper.
Reproduction. Sharks have a number of reproductive
strategies. Some enclose fertilized eggs in tough, leathery
egg cases that are released into the water for subsequent
development and birth. Some females retain eggs within
their bodies and hatch the young internally, so they are
born alive and fully formed. Others have a sophisticated
placental arrangement similar to that of mammals. Many
sharks take 10 to 20 years to mature sexually, and they produce
as few as one pup at a time. A number of species are
estimated to live for 40 or 50 years.