Page 8 - Shark

What is a shark?

Stingray Dorsal
Many people think of sharks as mean and menacing, with This puppet-show spaceship fin
is named after a close
their pointed snouts, fearsome teeth, and staring eyes. Sharks are relative of the shark
skillful predators, but only a few are a danger to people. The 450 or so (pp. 8–9).
species of shark range in size from a lantern shark, at about 8 in
(20 cm) long, to the whale shark, at over 40 ft (12 m) long, but half the species
are less than 3 ft (1 m) long. Not all sharks are as streamlined as this spinner
shark. Angel sharks have flattened bodies, horn sharks are blunt-headed,
while bamboo sharks are long and flexible. All sharks belong to one class of
fish called Chondrichthyes, having skeletons made of
gristlelike cartilage. Sharks live in the sea,
though a few live in or swim
into inland waters.

Long,
pointed
snout
Mouth beneath
snout, as in
most sharks Gill slits—
most sharks
Long have five
snout
Saw sharks Rounded Flattened Pectoral fin—helps lift shark in
body body water as it swims along and acts
as a brake, but cannot be folded
Mouth Mouth at Angel sharks up like those of a bony fish
below end of snout
snout No anal fin Side view of a
Bramble sharks spinner shark—a
Short
snout classic shark shape
Dogfish sharks
Rough sharks Anal fin Collared carpet sharks
Frilled shark Whale shark
Blind sharks
6–7 gill slits, 5 gill slits, Mouth in
Cow sharks 1 dorsal fin 2 dorsal fins front of eyes Nurse sharks
Wobbegongs
No fin
Fin spines spines Bamboo sharks Zebra shark
Hammerhead sharks
Horn sharks Mouth
behind eyes Thresher sharks
Requiem sharks
Nictitating (blinking) eyelid; spiral or stroll intestinal valve in gut No nictitating eyelid; ring intestinal valve in gut
Classification of living sharks
Weasel sharks Mackerel sharks

Smooth-hounds There are about 450 species of shark, which can be placed in eight groups, Basking shark
or orders, according to the presence or absence of certain external or internal
Barbeled hound shark characteristics, such as anal fins, fin spines, shape of the valve in the gut, Megamouth shark
and so on. When classifying any group of animals, scientists usually try to
False cat shark work out which are more closely related to each other and put those in a Crocodile shark
group together. But it is not always possible to sort out all the relationships,
Finback cat sharks so some may be grouped together just for convenience. Classification may Goblin shark
change when new sharks are discovered or when further studies reveal new
Cat sharks
relationships. Sand tigers