Page 324 - (DK) Ocean - The Definitive Visual Guide

322 ANIMAL LIFE

Sharks, Rays, and Chimaeras

SHARKS, RAYS, AND CHIMAERAS are often informally grouped
DOMAIN Eucarya HUMAN IMPACT
together as cartilaginous fish as they all have similar flexible
KINGDOM Animalia SHARK
skeletons. Within the group are some of Earth’s most efficient
PHYLUM Chordata FISHING
predators, such as the white shark, as well as filter feeders, such
CLASS Elasmobranchii
as the manta way. Some have features unusual for fish, such as Sharks are heavily fished all over
SUBCLASSES 2 the world for their meat, fins, liver
large brains, live birth, and warm blood. Fossils show that
SPECIES 1,290 oil, and skin. They reproduce very
cartilaginous fishes have changed little in form in hundreds of slowly, producing only a few
young every one to two years, and
millions of years. All have a skeleton of cartilage, teeth that are replaced by new ones many species take a decade or
when necessary, and toothlike scales covering their skin. snout more to reach full maturity. This
slow rate of both reproduction
mouth
nostril and growth means that shark
Anatomy pectoral fin populations cannot sustain heavy
gill slits fishing pressure, and take many
The internal skeleton of all the fishes in this group is made from years to recover. Worldwide, most
flexible cartilage. In some species, parts of the skull and skeleton stocks are currently being fished at
rates above safe biological limits.
are strengthened by mineral deposits. The teeth are covered by
very hard enamel and are formidable weapons. Sharks have several
rows of teeth lying flat behind the active ones. These gradually
move forward, and individual teeth may be replaced as often as
every 8–15 days. Cartilaginous fishes have extremely tough skin. It
is extra-thick in female sharks because males use their teeth to hold pelvic fin
onto them when mating. A shark’s skin is covered in tiny, backward- RAY BODY SHAPE
pointing, toothlike structures called dermal denticles, which feel like cloaca Skates and rays have flat
sandpaper. Rays have scattered denticles, some enlarged to form spines, tail bodies and large pectoral
fins. The mouth is on the
while chimaeras mostly have no denticles. Unlike bony fishes (see underside, so water for
pp.338–41), cartilaginous fishes do not have a breathing is sucked in through SHARK FINS
first dorsal fin
gas-filled swim bladder. Sharks living in the a pair of holes, called spiracles, Thousands of sharks are killed every year for
open ocean, however, often have a very on the upper side, then passed their valuable fins, which are dried and then
made into shark-fin soup. The body is often
large, oil-filled liver, which aids buoyancy. over the gills. discarded while the shark is still alive.
gill slit
second dorsal fin
eye

pelvic fin underslung
anal fin
mouth
heterocercal tail pectoral fin
SHARK BODY SHAPE
A typical shark has a sleek, streamlined body.
Most sharks have a tail that is asymmetrical
(heterocercal), and thethe paired pelvic fins
are set far back. The mouth is underslung,
and there are five gill slits on each side.
serrated,
daggerlike bladelike edge
point grips cuts like a knife
flesh

SANDTIGER TIGER SHARK
SHARK
palate, covered
with flat teeth,
crushes food

OCEAN LIFE TOOTH ADAPTATIONS
RAY

Sharks’ teeth are shaped to suit their diet.
Pointed ones are used for holding, while
serrated teeth slice chunks from prey. Rays
and chimaeras have teeth like grindstones
to crush hard crustaceans and mollusks.