Page 9 - Shark

thouSandS oF teeth Jaws and Skin of ScaleS
Sharks never run out of teeth. teeth of bramble Most bony fish
When the front ones become sand tiger shark have scales
worn or break, they are replaced shark covering their
by new ones in the row behind skins. Scales are
(right). Some sharks shed one not replaced, but
or two teeth at a time, while increase in size as
others, like spiny dogfish and the fish grows.
cookiecutters (pp. 44–45), replace
a whole row at a time. As the Fish scale
shark grows, its new teeth are
larger than the ones replaced. rough Skin
During its life, a shark will Sharks are covered in small,
replace thousands of teeth. Each toothlike denticles that give the skin a rough feel if
new tooth forms in the shark’s stroked the wrong way. Bramble sharks (above) have
gums and rotates forward until it large denticles scattered over the skin rather than
eventually drops out. Sharks’ teeth a continuous cover as in other sharks. As sharks
are embedded in their gums and are grow, the denticles are shed and replaced by
not directly attached to their jaws, like slightly larger ones, in the same way the
those of bony fish. teeth are replaced. The structure
of a denticle is the same as a
shark’s tooth.

Shark vS. FiSh
Sharks, rays, skates,
and chimeras are
cartilaginous fish
belonging to the class
Chondrichthyes. Their
skeletons are light and
rubbery (to aid buoyancy),
Caudal fin unlike those of bony fish,
Pelvic fin—acts as a Anal which are more rigid.
stabilizer to prevent fin Most bony fish have
shark from rolling ray-fins, like the bib
Spinning in circleS (left). The most notable
The spinner shark is named for its First differences between
habit of spinning around on its axis, Second dorsal dorsal sharks and bony fish
which it does to confuse its fish fin fin are that bony fish have
prey as it hunts in a school of fish. Third a gill cover, or operculum,
Spinner sharks grow to 8 ft (2.5 m) dorsal Side instead of gill slits, and scales
long and live in the warm coastal fin view of instead of denticles. Bony fish
and deeper waters of the Atlantic, a bib also have a swim bladder, or
Indian, and western gas-filled sac, which helps
Pacific Oceans. them control their buoyancy.

Barbel
Symmetrical Operculum, or
caudal fin, with covering for gills
samesize upper and
lower lobe Second ratFiSh
anal fin Pelvic fin Pectoral fin Chimeras, or ratfish,
Air bladder are distant relatives
First anal fin of sharks and have
Full oF air ratlike tails and
Bony fish have a swim, or air, bladder beaklike teeth. They
inside their bodies. When gas is taken live in the ocean
into the bladder, the fish becomes more depths.
buoyant and rises toward the surface. By The small hook
reabsorbing gases from the bladder, it can on a chimera’s
sink. Sharks lack swim bladders and most head is similar
will sink if they stop swimming, but to ones
they have oil-rich livers that reduce their found on
weight in water. Basking sharks have fossil sharks
Swim such large livers that they can stay at the (pp. 12–13)
bladder of a fish surface while swimming slowly. Chimera