Contents Introducing Wonders of the Sea 9 ●
Life in the Sea 10 The World of Plankton 12 Sponges, Anemones and Jellyfish 14 The World of Mollusks 16 Life on a Sandy Beach 18 Squid and Octopuses 20 Crustaceans 22 Sea Stars, Urchins and Worms 24 Life on a Rocky Shore 26 Rays and Sawfish 28 Sharks 30 The World of Eels 32 Life on a Coral Reef 34 Prickly and Poisonous 36 Pacific Salmon 38 Silvery Schooling Fish 40 Life in a Mangrove 42 Deep-sea Fish 44 Fast-swimming Fish 46 Seahorses and Shrimpfish 48 Life at a Deep-sea Vent 50 The World of Flatfish 52 Wonders of the Deep 54 ●
Glossary of Key Words 56 Index 57
INTRODUCING
Wonders of the Sea There is more sea than land on our planet and it is home to many amazing creatures. Along the beach there are mollusks and crabs. Out at sea live spiny lobsters, creatures with eight long arms and fish with wings. Life began in the salty seas millions of years ago. All the layers of the oceans are inhabited, even the deepest, darkest parts that are out of our reach. There may be mysterious creatures down there that we have yet to find.
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WONDERS
OF THE
SEA
The World of Plankton Billions of microscopic plants and
animals drift in the surface waters of the seas and oceans. They are called plankton. These plants and animals are very important for underwater life because they begin the food chain in the sea. Plant plankton are eaten by animal plankton, which in turn are eaten by larger sea creatures. Many sea animals depend on tiny plankton for their food.
Jellyfish larva, a type of animal plankton
Crab larva, or young crab
ANIMAL PLANKTON Some sea creatures, including crabs, some fish and sea gooseberries, begin life in the sea as animal plankton. These larvae, or young, look very different from the adult animals. Other creatures, such as copepods, stay as plankton all their lives.
Sea gooseberries, a type of animal plankton
Small fish has large eyes to keep a lookout for predators
Young fish feeds on other animal plankton
Fish larva, a type of animal plankton
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THE WORLD
OF
PLANKTON
MICROSCOPIC LIFE Collect some sea water in a bucket or glass jar. It may be possible to see plankton clumped together as coloured patches in the water with a naked eye. For a closer view, place a few drops of the water on a plate and look through a microscope.
Using a microscope to see plankton
PLANT PLANKTON Plant plankton
Each plant plankton is made up of only one cell. Millions of tons of new plant plankton grow every year. They are called the grass of the sea because so many animals feed on them. Plant plankton use sunlight to make their own food.
AMAZING FACTS
Single-celled plant plankton float together in a chain Long antennae, or feelers, help the copepod probe for food
★ Some kinds of dinoflagellates, tiny plant plankton, give off light. If a boat or swimming creature disturbs the surface of the sea at night, the dinoflagellates glow and sparkle in the dark.
Copepod, a tiny crustacean
Dinoflagellates glow in the dark
EAT OR BE EATEN Animal plankton, such as arrow worms, eat smaller animals or plant plankton. Most things that live in the sea will become food for something else.
FIND OUT MORE THE HUMAN BODY: Cells INSECTS AND SPIDERS: Crustaceans
Arrow worm
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WONDERS
OF THE
SEA
The World of Mollusks Beaches are littered with empty
shells. Many of these were once the homes of soft-bodied sea creatures, called mollusks, which include clams, oysters, mussels and sea snails. Over time, these mollusks use a chalky substance found in sea water to build their shells, which help to protect them from enemies. Sea slugs, squid and octopuses are also mollusks, but they do not have shells.
Purple sea snail hangs from its bubble raft, waiting for food Bubbles are made from slime produced in the snail’s body
FLOATING ON BUBBLES The purple sea snail lives near the surface of the sea. It cannot swim, so to stay afloat it makes a “raft” from hundreds of bubbles it has blown and stuck together. If it is separated from its raft, the snail sinks to the seabed and dies.
DOUBLE OR SINGLE SHELLS Some mollusks, such as clams and scallops, have two shells, joined together by a hinge. They are called bivalves. Others, such as snails and whelks, have only one shell. They are called gastropods. Whelk hunts other creatures to eat
Siphons, or tubes, for filtering food from the water
Warty venus clam, a typical bivalve
Scallop closing the two halves of its shell
Jet of water shoots scallop backward
“CLAPPING” SCALLOPS
Muscular “foot” helps mollusks move European whelk, a typical gastropod
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Scallops can move fast when escaping from enemies, such as sea stars. They open their shells to draw water in, then clap them together to squirt it out again. This shoots them backward through the water, out of reach.
THE WORLD
OF
MOLLUSKS
AMAZING FACTS
★ The biggest shell of all
Purple sea snail clinging to bubbles
belongs to the giant clam. Some clam shells are more than 1 m (3 ft) wide and weigh a quarter of a ton. Giant clam and diver
HOW A PEARL GROWS An irritating piece 1 of grit or sand gets stuck inside an oyster’s shell. To protect its soft 2 body, the oyster covers the grit with mother-of-pearl (nacre) from the lining of its shell.
As sea snail grows, it builds extra sections onto its curved shell
Sea snail eats small sea animals, such as jellyfish
After a year or 3 more, a smooth, round pearl has formed inside the oyster, and there is no longer any irritation.
Opened oyster shell, with pearl
FIND OUT MORE INSECTS AND SPIDERS: Mollusks THE MARVELS OF SCIENCE: Floating
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WONDERS
OF THE
SEA
Life on a Sandy Beach Every day, the sea rises
and falls along the shore. These changing tides can cause problems for creatures of the seashore. At low tide, they need a damp place to hide so they will not dry out. When the tide comes in, animals have to take shelter so they do not get swept away by the waves. A sandy beach may look empty, but plenty of creatures live just below the surface of the sand. These include worms, mollusks, crabs and even burrowing fish. When the tide goes out, lesser sand eels dig themselves into the sand. They stay in their damp burrows until the sea floods in again.
SHORE-LIVING CRABS Crabs belong to a group of hard-shelled creatures called crustaceans. Some crabs live in deep water, but others live on sandy shores, where they search for mollusks and other food. If in danger, the crabs burrow into the sand. When in its burrow, the masked, or helmet, crab can breathe through a long tube made from its antennae. Channel wrack seaweed Empty cockle shell washed up on the beach at high tide
Sea stars, or starfish, feed on mollusks
Lugworm in its burrow
Masked, or helmet, crab
Lesser sand eels
Sandmason worm collects food in its tentacles
Red ribbon worm grows up to 15 cm (6 in) long
SPINY DIGGER The heart urchin is a type of sea urchin. It uses its strong, broad spines to dig into the sand in search of food. It feeds on tiny pieces of plant and animal food.
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LIFE
ON A
SANDY BEACH
BEACHCOMBING The tide washes up many fascinating things onto the beach. Look for mollusk shells, the egg cases of sharks and rays, called mermaids’ purses and dead crabs. Remember – only empty shells should be collected. Look out for seashells and egg cases on the beach
UNDERGROUND MOLLUSKS Many clams and other mollusks hide just beneath the sandy surface. When the tide comes in, they push up a tube, take in water, and feed on tiny scraps of food they filter from the water. One clam, the razor shell, can burrow into the sand faster than a person can dig. Lugworm cast at one end of its burrow
Cockle feeds on plankton
Common whelk searches the shore for food
Animal life on a sandy seashore Tellin clam has two siphons, or tubes, for breathing and filtering food
BURROWING WORMS Ribbon worms, ragworms and lugworms all burrow into the sand. Lugworms leave little coils of sand, called casts, on the beach at one end of their U-shaped burrows. Peacock worms live in tubes made of grains of sand stuck together with slimy mucus. Sea mouse, a type of worm
Ribbon worm Peacock worm Heart urchin has long feeding tubes Razor shell, shaped like an old-fashioned razor
FIND OUT MORE BIRDS: Shore birds PLANET EARTH: Tides
Ragworm with segmented body
Sand gaper, a clam
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WONDERS
OF THE
SEA
Squid and Octopuses Squid, octopuses and cuttlefish
Octopus reacts fast when attacked and escapes behind an inky “smokescreen”
are mollusks, but they do not have shells to protect their soft, bag-shaped bodies. All have eight long arms, but squid and cuttlefish also have a pair of tentacles, which they use for catching prey. Octopuses have excellent eyesight and large brains. They are believed to be the most intelligent of all invertebrate animals.
School of squid
SPEEDY SQUID Squid often travel in groups called schools. Squid can swim, in short bursts, at speeds of up to 32 km/h (20 mph). Water is taken into the body, then squirted out through a tube near the neck. This forces the squid through the water.
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Two rows of suckers line each arm Funnel directs a squirt of water to jet the octopus backward
INK SQUIRTERS Octopuses squirt out thick clouds of brown or black ink to confuse their enemies. This gives them time to make a quick getaway. The ink comes from a special sac, or bag, in the octopus’s body. Squid and cuttlefish produce ink, too.
WONDERS
OF THE
Sea Stars, Urchins and Worms Spiny sea stars and sea
SEA
AMAZING FACTS
★ Some sea stars have eyes on the ends of their arms.
urchins belong to a group called echinoderms. Their prickly spines protect them from enemies. They have hundreds of feet like tiny tubes, which they use to crawl over the seabed. Many types of worms also live in the sea. Some are good swimmers but others spend their lives in burrows.
★ The sunflower star is one of the biggest of all sea stars. It measures about 132 cm (52 in) from tip to tip. Large mouth lies under the centre of the body
Sea star preying on a clam
Sea star squeezes its stomach inside the shell and digests the clam’s flesh
SEEING STARS A sea star, or starfish, has a central body, with five or more arms around it. If an arm is damaged, the sea star grows a new one within a few weeks. Sea stars eat mollusks and corals.
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SEA STARS, URCHINS Sea urchin
Pincer Sucker
Spine Sharp spines with suckers and pincers among them
AND
WORMS
STICKY DEFENSE The sea cucumber is not a plant – it is related to sea stars and sea urchins. It defends itself by shooting out a stream of sticky threads. While the attacker untangles itself, the sea cucumber moves away on its tube feet.
Sea cucumber clings to stones with its tiny suckers
SPINY SHELLS Sea urchins have hard, round shells covered in sharp, poisonous spines. They use their spines as weapons for self-defense. Some also use them for burrowing into the sand. The suckers and pincers are used for seizing prey. Prickly spines Long, strong arms wrap around clam Suckers on the end of tiny tube feet force the clam shell open Clam trapped by sea star
SEA-LIVING WORMS Sea worms have many different lifestyles. Fan worms wave their feathery tentacles to trap food. The fire worm is an active hunter, covered with stinging bristles. The hairy sea mouse hides in mud or sand on the seabed.
Fan worms anchored to seabed
Tentacles Fire worm
Stinging bristles Body covered with fine hair
Sea mouse
FIND OUT MORE THE HUMAN BODY: Stomach INSECTS AND SPIDERS: Worms
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