Invertebrates

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Written by Brooke Bessesen

InvertebratesA Science A–Z Life Series

Word Count: 1,041

Key elements Used in this BooKthe Big idea: Animals are categorized as either vertebrates or invertebrates. Vertebrates have a spine, while invertebrates do not. Invertebrates are extremely diverse and represent the largest proportion of all animals on Earth. Spiders, snails, beetles, octopuses, worms, and sea sponges are some of the many types of invertebrates. The Invertebrates unit explores six groups of invertebrates—poriferans, cnidarians, echinoderms, mollusks, annelids, and arthropods. Understanding invertebrates helps students appreciate the rich variety of animal life on Earth. They are important as members of food webs, as decomposers, and as pollinators. As we learn about invertebrates and recognize them as important living things, we may change how we interact with them. We may even take action to protect them and ensure their survival.Key words: abdomen, arachnids, arthropods, backbone, bivalves, classify, cold-blooded, crustaceans, gills, insects, invertebrates, mollusks, spine, sponges, symmetry, tentacles, vertebrae, vertebrates

Key comprehension skill: Classify informationOther suitable comprehension skills: Compare and contrast; cause and effect; elements of a genre; identify facts; interpret graphs, charts, and diagrams; using a glossary and boldfaced terms; using a table of contents and headings

Key reading strategy: Connect to prior knowledgeOther suitable reading strategies: Ask and answer questions; summarize; visualize; retell

Written by Brooke Bessesen

www.sciencea-z.com

Invertebrates

Invertebrates / © Learning A–Z / Written by Brooke Bessesen All rights reserved. / www.sciencea-z.com

Photo Credits: Front cover: © iStockphoto.com/Chanyut Sribua-rawd; back cover, page 4 (bottom right): © iStockphoto.com/Gewoldi; title page: © iStockphoto.com/Prill Mediendesign & Fotografie; page 4 (top): © Learning A–Z; page 4 (bottom left): © iStockphoto.com/Christian Musat; page 4: (left inset): © iStockphoto.com/Erik Bettini; page 4 (right inset), page 13 (top): © iStockphoto.com/Laurel Stewart; page 5 (top): © Gregg Williams/Dreamstime.com; page 5 (center): © iStockphoto.com/Daniel Hyams; page 5 (bottom), page 9: © iStockphoto.com/Piero Malaer; page 6 (left): © iStockphoto.com/DK Images; page 6 (right): © iStockphoto.com/Nick M. Do; page 7 (top): © DK Images; page 7 (center right): © iStockphoto.com/ Emmanouil Filippou; page 7 (bottom right): © Alexey Kalinin/Dreamstime.com; page 7 (bottom left): © iStockphoto.com/Boris Katsman; page 10: © Paul Sutherland/National Geographic Stock; page 11: © iStockphoto.com/Olga Khoroshunova; page 12 (top): © iStockphoto.com/Kevin Marlow; page 12 (bottom): © iStockphoto.com/Emmanouil Gerasidis; page 13 (bottom left): © iStockphoto.com/Generistock; page 13 (bottom right): © Brandon D. Cole/Corbis; page 14: © Reuters/Alexandra Beier; page 15 (top): © iStockphoto.com/Dinamir Predov; page 15 (bottom): © iStockphoto.com/4kodiak; page 16: © iStockphoto.com/Dusty Cline; page 17: © Maxim Shishkanov/Dreamstime.com; page 18 (top): © iStockphoto.com/Proxyminder; page 18 (bottom): © Don Farrall/Digital Vision/Getty Images; page19 (bottom right): © iStockphoto.com/Mark Kostich; page 19 (top): © iStockphoto.com/Eric Isselée; page 19 (bottom left): © iStockphoto.com/James Allred; page 19 (bottom center): © iStockphoto.com/Lezh; page 20 (top to bottom): © iStockphoto.com/Jill Chen; page 20 (2): © iStockphoto.com/Nishad Narod; page 20 (3): © iStockphoto.com/Guillermo Lobo; page 20 (4): © iStockphoto.com/Jeridu; page 20 (5): © James Steidl/Dreamstime.com; page 22 (left): © iStockphoto.com/Steve Debenport; page 22 (center): © iStockphoto.com/Slavoljub Pantelic; page 22 (right group; left to right, top to bottom): © iStockphoto.com/ Mark Kostich; © iStockphoto.com/Laurel Stewart; © iStockphoto.com/Dinamir Predov; © iStockphoto.com/ Jill Chen; © iStockphoto.com/Lezh; © iStockphoto.com/Nishad Narod; © iStockphoto.com/Nick M. Do; © iStockphoto.com/Eric Isselée; © iStockphoto.com/4kodiak; © Maxim Shishkanov/Dreamstime.com; © iStockphoto.com/Jeridu; © iStockphoto.com/Dusty Cline

23 24

Glossary

arachnids a group of arthropods that have two body segments and eight legs; includes spiders and scorpions (p. 19)

arthropods a group of invertebrates that have a segmented body, a hard, skinlike shell, and jointed limbs; includes insects, arachnids, and crustaceans (p. 17)

crustaceans a group of mostly aquatic arthropods that have a segmented body and several pairs of legs; includes crabs and shrimp (p. 20)

insects a group of small arthropods that have six legs, three body parts, and usually two sets of wings; includes bees and ants (p. 17)

invertebrates animals that have no backbone (p. 4)

mollusks a group of invertebrates that have a soft, unsegmented body, and most have one or two shells; includes snails and octopuses (p. 14)

spine a column of bones that provides the main support for a vertebrate’s body; the backbone, or vertebral column (p. 4)

sponges a group of primitive marine invertebrates with a porous body that permanently attaches to a solid surface in adulthood (p. 9)

symmetry the property of having the same size and shape across a dividing line, or having one half identical to the other half (p. 6)

vertebrates animals that have a backbone (p. 4)

Index

arachnids, 19bivalves, 15crustaceans, 20, 21gills, 15

pollinators, 18prey, 20symmetry, 6, 9tentacles, 10, 11

Key elements Used in this BooKthe Big idea: Animals are categorized as either vertebrates or invertebrates. Vertebrates have a spine, while invertebrates do not. Invertebrates are extremely diverse and represent the largest proportion of all animals on Earth. Spiders, snails, beetles, octopuses, worms, and sea sponges are some of the many types of invertebrates. The Invertebrates unit explores six groups of invertebrates—poriferans, cnidarians, echinoderms, mollusks, annelids, and arthropods. Understanding invertebrates helps students appreciate the rich variety of animal life on Earth. They are important as members of food webs, as decomposers, and as pollinators. As we learn about invertebrates and recognize them as important living things, we may change how we interact with them. We may even take action to protect them and ensure their survival.Key words: abdomen, arachnids, arthropods, backbone, bivalves, classify, cold-blooded, crustaceans, gills, insects, invertebrates, mollusks, spine, sponges, symmetry, tentacles, vertebrae, vertebrates

Key comprehension skill: Classify informationOther suitable comprehension skills: Compare and contrast; cause and effect; elements of a genre; identify facts; interpret graphs, charts, and diagrams; using a glossary and boldfaced terms; using a table of contents and headings

Key reading strategy: Connect to prior knowledgeOther suitable reading strategies: Ask and answer questions; summarize; visualize; retell

Written by Brooke Bessesen

www.sciencea-z.com

Invertebrates

Invertebrates / © Learning A–Z / Written by Brooke Bessesen All rights reserved. / www.sciencea-z.com

Photo Credits: Front cover: © iStockphoto.com/Chanyut Sribua-rawd; back cover, page 4 (bottom right): © iStockphoto.com/Gewoldi; title page: © iStockphoto.com/Prill Mediendesign & Fotografie; page 4 (top): © Learning A–Z; page 4 (bottom left): © iStockphoto.com/Christian Musat; page 4: (left inset): © iStockphoto.com/Erik Bettini; page 4 (right inset), page 13 (top): © iStockphoto.com/Laurel Stewart; page 5 (top): © Gregg Williams/Dreamstime.com; page 5 (center): © iStockphoto.com/Daniel Hyams; page 5 (bottom), page 9: © iStockphoto.com/Piero Malaer; page 6 (left): © iStockphoto.com/DK Images; page 6 (right): © iStockphoto.com/Nick M. Do; page 7 (top): © DK Images; page 7 (center right): © iStockphoto.com/ Emmanouil Filippou; page 7 (bottom right): © Alexey Kalinin/Dreamstime.com; page 7 (bottom left): © iStockphoto.com/Boris Katsman; page 10: © Paul Sutherland/National Geographic Stock; page 11: © iStockphoto.com/Olga Khoroshunova; page 12 (top): © iStockphoto.com/Kevin Marlow; page 12 (bottom): © iStockphoto.com/Emmanouil Gerasidis; page 13 (bottom left): © iStockphoto.com/Generistock; page 13 (bottom right): © Brandon D. Cole/Corbis; page 14: © Reuters/Alexandra Beier; page 15 (top): © iStockphoto.com/Dinamir Predov; page 15 (bottom): © iStockphoto.com/4kodiak; page 16: © iStockphoto.com/Dusty Cline; page 17: © Maxim Shishkanov/Dreamstime.com; page 18 (top): © iStockphoto.com/Proxyminder; page 18 (bottom): © Don Farrall/Digital Vision/Getty Images; page19 (bottom right): © iStockphoto.com/Mark Kostich; page 19 (top): © iStockphoto.com/Eric Isselée; page 19 (bottom left): © iStockphoto.com/James Allred; page 19 (bottom center): © iStockphoto.com/Lezh; page 20 (top to bottom): © iStockphoto.com/Jill Chen; page 20 (2): © iStockphoto.com/Nishad Narod; page 20 (3): © iStockphoto.com/Guillermo Lobo; page 20 (4): © iStockphoto.com/Jeridu; page 20 (5): © James Steidl/Dreamstime.com; page 22 (left): © iStockphoto.com/Steve Debenport; page 22 (center): © iStockphoto.com/Slavoljub Pantelic; page 22 (right group; left to right, top to bottom): © iStockphoto.com/ Mark Kostich; © iStockphoto.com/Laurel Stewart; © iStockphoto.com/Dinamir Predov; © iStockphoto.com/ Jill Chen; © iStockphoto.com/Lezh; © iStockphoto.com/Nishad Narod; © iStockphoto.com/Nick M. Do; © iStockphoto.com/Eric Isselée; © iStockphoto.com/4kodiak; © Maxim Shishkanov/Dreamstime.com; © iStockphoto.com/Jeridu; © iStockphoto.com/Dusty Cline

23 24

Glossary

arachnids a group of arthropods that have two body segments and eight legs; includes spiders and scorpions (p. 19)

arthropods a group of invertebrates that have a segmented body, a hard, skinlike shell, and jointed limbs; includes insects, arachnids, and crustaceans (p. 17)

crustaceans a group of mostly aquatic arthropods that have a segmented body and several pairs of legs; includes crabs and shrimp (p. 20)

insects a group of small arthropods that have six legs, three body parts, and usually two sets of wings; includes bees and ants (p. 17)

invertebrates animals that have no backbone (p. 4)

mollusks a group of invertebrates that have a soft, unsegmented body, and most have one or two shells; includes snails and octopuses (p. 14)

spine a column of bones that provides the main support for a vertebrate’s body; the backbone, or vertebral column (p. 4)

sponges a group of primitive marine invertebrates with a porous body that permanently attaches to a solid surface in adulthood (p. 9)

symmetry the property of having the same size and shape across a dividing line, or having one half identical to the other half (p. 6)

vertebrates animals that have a backbone (p. 4)

Index

arachnids, 19bivalves, 15crustaceans, 20, 21gills, 15

pollinators, 18prey, 20symmetry, 6, 9tentacles, 10, 11

21 22

Conclusion

Invertebrates have a lot in common.

They also have many differences.

Earth has many more invertebrates

than vertebrates. Most invertebrates

are much smaller than humans. But

together, they would weigh more

than all the people in the world.

Invertebrates are very important.

They may be spineless, but they are

the “backbone” of the natural world.

invertebrate information

Spongesnowadays, sponges used in sinks and showers are factory-made, but people used to use real sponges from the sea.

Corals

coral reefs provide shelter for many marine animals. reefs can also protect shoreline habitats by stopping giant waves.

Sea urchinssome sea urchins can live for over 200 years.

Clams, oysters, and mussels

mollusks provide a food source for many animals, including some humans.

Wormsdoctors sometimes use leeches to bring blood into fingers that have been sewn back on.

Insectsfrogs, toads, some birds, and many other animals survive on a diet mainly or entirely made up of insects.

Spidersby eating so many insects, spiders help control the number of insects in the world.

Crustaceansmany large marine animals eat tiny crustaceans called krill. blue whales eat 8,000 pounds of krill a day.

Millipedesmillipedes are important decomposers. they help break down dead plant life.

interesting invertebrate information

All humans

All invertebrates

3

Introduction

Invertebrates are “spineless” animals.

That means they have no backbone.

Feel the bumps in the

middle of your back. The

bones of your backbone,

or spine, are called

vertebrae (VER-tuh-bray).

Animals with a spine are called

vertebrates. You are a vertebrate.

But most animals are invertebrates.

4

Table of Contents

Introduction ...................................... 4

What Do Invertebrates Have in Common? ...................... 5

Classifying Invertebrates ................ 7

Sponges .............................................. 9

Sea Jellies, Corals, and Sea Anemones .................... 10

Sea Urchins, Sea Stars, and Sand Dollars ....................... 12

Octopuses, Squids, Snails, and Clams ................................... 14

Worms .............................................. 16

Insects, Spiders, Lobsters, and Millipedes ........................... 17

Conclusion ...................................... 22

Glossary ........................................... 23

Index ................................................ 24

InvertebratesVertebrates

3

Introduction

Invertebrates are “spineless” animals.

That means they have no backbone.

Feel the bumps in the

middle of your back. The

bones of your backbone,

or spine, are called

vertebrae (VER-tuh-bray).

Animals with a spine are called

vertebrates. You are a vertebrate.

But most animals are invertebrates.

4

Table of Contents

Introduction ...................................... 4

What Do Invertebrates Have in Common? ...................... 5

Classifying Invertebrates ................ 7

Sponges .............................................. 9

Sea Jellies, Corals, and Sea Anemones .................... 10

Sea Urchins, Sea Stars, and Sand Dollars ....................... 12

Octopuses, Squids, Snails, and Clams ................................... 14

Worms .............................................. 16

Insects, Spiders, Lobsters, and Millipedes ........................... 17

Conclusion ...................................... 22

Glossary ........................................... 23

Index ................................................ 24

InvertebratesVertebrates

21 22

Conclusion

Invertebrates have a lot in common.

They also have many differences.

Earth has many more invertebrates

than vertebrates. Most invertebrates

are much smaller than humans. But

together, they would weigh more

than all the people in the world.

Invertebrates are very important.

They may be spineless, but they are

the “backbone” of the natural world.

invertebrate information

Spongesnowadays, sponges used in sinks and showers are factory-made, but people used to use real sponges from the sea.

Corals

coral reefs provide shelter for many marine animals. reefs can also protect shoreline habitats by stopping giant waves.

Sea urchinssome sea urchins can live for over 200 years.

Clams, oysters, and mussels

mollusks provide a food source for many animals, including some humans.

Wormsdoctors sometimes use leeches to bring blood into fingers that have been sewn back on.

Insectsfrogs, toads, some birds, and many other animals survive on a diet mainly or entirely made up of insects.

Spidersby eating so many insects, spiders help control the number of insects in the world.

Crustaceansmany large marine animals eat tiny crustaceans called krill. blue whales eat 8,000 pounds of krill a day.

Millipedesmillipedes are important decomposers. they help break down dead plant life.

interesting invertebrate information

All humans

All invertebrates

Crustaceans (kruh-STAY-shuns) are

arthropods that have

many pairs of walking

legs. Most live in

water. Crabs, lobsters,

crayfish, and shrimp

are in this group.

These invertebrates

eat many foods, such

as fish, mollusks, worms, and plants.

Millipedes and centipedes are also

arthropods. They look like worms,

but they have many

legs. Centipedes

have two front

claws to put

poison into

animals they eat.

lobster

19 20

Spiders, ticks, mites, and scorpions

are in a group of arthropods called

arachnids (uh-RAK-nidz). All these

animals have a special mouth to

help them eat other animals.

Spiders have eight legs for walking

and climbing. Their body has two

parts. The front part has the eyes,

mouth, and legs. The back

part is the abdomen.

Spiders make webs

to catch insects.

Webs are also

used as nests for

young spiders.

milipede

centipede

spidermite tick

crab

shrimp

scorpion

What Do Invertebrates

Have in Common?

Invertebrates have many things

in common. You already know

they have no spine. But they have

other things in common, too:

• Like all animals, invertebrates

have more than

one cell.

• All invertebrates

move their body

in some way.

• Invertebrates

need oxygen,

but they do not

breathe as we do.

5 6

• Most invertebrates have symmetry.

That means the sides of their body

look alike.

• Invertebrates can’t make their

own heat. They are cold-blooded.

• Most invertebrates make young

with sperm from males and eggs

from females.

• Invertebrates eat to stay alive.

In this book, you will learn about

some groups of invertebrates. You

will find out how they move and eat.

fly

swim

crawl

These invertebrates have different ways of moving.

radial symmetrybilateral symmetry

What Do Invertebrates

Have in Common?

Invertebrates have many things

in common. You already know

they have no spine. But they have

other things in common, too:

• Like all animals, invertebrates

have more than

one cell.

• All invertebrates

move their body

in some way.

• Invertebrates

need oxygen,

but they do not

breathe as we do.

5 6

• Most invertebrates have symmetry.

That means the sides of their body

look alike.

• Invertebrates can’t make their

own heat. They are cold-blooded.

• Most invertebrates make young

with sperm from males and eggs

from females.

• Invertebrates eat to stay alive.

In this book, you will learn about

some groups of invertebrates. You

will find out how they move and eat.

fly

swim

crawl

These invertebrates have different ways of moving.

radial symmetrybilateral symmetry

Crustaceans (kruh-STAY-shuns) are

arthropods that have

many pairs of walking

legs. Most live in

water. Crabs, lobsters,

crayfish, and shrimp

are in this group.

These invertebrates

eat many foods, such

as fish, mollusks, worms, and plants.

Millipedes and centipedes are also

arthropods. They look like worms,

but they have many

legs. Centipedes

have two front

claws to put

poison into

animals they eat.

lobster

19 20

Spiders, ticks, mites, and scorpions

are in a group of arthropods called

arachnids (uh-RAK-nidz). All these

animals have a special mouth to

help them eat other animals.

Spiders have eight legs for walking

and climbing. Their body has two

parts. The front part has the eyes,

mouth, and legs. The back

part is the abdomen.

Spiders make webs

to catch insects.

Webs are also

used as nests for

young spiders.

milipede

centipede

spidermite tick

crab

shrimp

scorpion

18

Insects, Spiders, Lobsters,

and Millipedes

Arthropods

Arthropods (AR-thruh-pods) are

invertebrates with a hard, skinlike

shell. Their body has different parts,

and their legs can bend.

Insects are arthropods with three

body parts. They have two antennae

and six legs. They use their legs to

run, jump, swim, and even to make

sounds. Many also have wings.

Insects come from

eggs. Their body

changes shape

three or four times

during their life.

Ants, beetles, and

flies are just a few

of the different

kinds of insects.

Most animals on

Earth are insects!

Some insects are

pollinators. When

they drink from flowers, they pick

up and carry pollen to other flowers.

Many plants could not make fruit

without the help of insects.

17

a honeybee exploring a flower

Three stages in the life cycle of a butterfly

insect body Parts

head

two antennae wingsthorax abdomen

six legs

Classifying Invertebrates

Invertebrates have things

in common, but they

are very different, too.

A fruit fly is smaller

than a grain of rice.

A giant squid can

be as long as a bus.

Centipedes eat worms. Butterflies

drink from flowers. Bees fly, and

crabs crawl. Earth has many, many

kinds of invertebrates!

7

Scientists classify, or group, animals

by the things they have in common.

Animals are either vertebrates or

invertebrates. Each kind is made

up of smaller groups.

Read on to learn about some groups

of invertebrates.

8

vertebrates

Mammals Birds Reptiles Amphibians Fish

invertebrates*

Poriferans

Cnidarians

Echinoderms

Mollusks

Annelids

Arthropods

sponges

sea jelliescorals

sea anemones

earthworms

octopusessquidssnailsclams

insectsspiderslobsters

millipedes

sea starssea urchinssand dollars

Invertebrates can be very different from each other.

Giant squids have eyes bigger than basketballs!

*These are the invertebrate groups covered in this book.

Classifying Invertebrates

Invertebrates have things

in common, but they

are very different, too.

A fruit fly is smaller

than a grain of rice.

A giant squid can

be as long as a bus.

Centipedes eat worms. Butterflies

drink from flowers. Bees fly, and

crabs crawl. Earth has many, many

kinds of invertebrates!

7

Scientists classify, or group, animals

by the things they have in common.

Animals are either vertebrates or

invertebrates. Each kind is made

up of smaller groups.

Read on to learn about some groups

of invertebrates.

8

vertebrates

Mammals Birds Reptiles Amphibians Fish

invertebrates*

Poriferans

Cnidarians

Echinoderms

Mollusks

Annelids

Arthropods

sponges

sea jelliescorals

sea anemones

earthworms

octopusessquidssnailsclams

insectsspiderslobsters

millipedes

sea starssea urchinssand dollars

Invertebrates can be very different from each other.

Giant squids have eyes bigger than basketballs!

*These are the invertebrate groups covered in this book.

18

Insects, Spiders, Lobsters,

and Millipedes

Arthropods

Arthropods (AR-thruh-pods) are

invertebrates with a hard, skinlike

shell. Their body has different parts,

and their legs can bend.

Insects are arthropods with three

body parts. They have two antennae

and six legs. They use their legs to

run, jump, swim, and even to make

sounds. Many also have wings.

Insects come from

eggs. Their body

changes shape

three or four times

during their life.

Ants, beetles, and

flies are just a few

of the different

kinds of insects.

Most animals on

Earth are insects!

Some insects are

pollinators. When

they drink from flowers, they pick

up and carry pollen to other flowers.

Many plants could not make fruit

without the help of insects.

17

a honeybee exploring a flower

Three stages in the life cycle of a butterfly

insect body Parts

head

two antennae wingsthorax abdomen

six legs

I am a mollusk with two shells and one foot. I can turn a grain of sand into a pearl. Who am I?

oyster

16

Not all mollusks are fast. Land snails

and slugs are slow. They make slime

to help them slide. Snails and slugs

have a special tool in their mouth

that helps

them eat as

they move.

Snails have one shell. But mollusks

called bivalves have two. Oysters

and clams are in this second group.

Some bivalves swim by clapping

their shells. Most of them eat food

from water that passes through

their gills.

15

Worms

Annelids

Worms are invertebrates,

too. There are many

different groups of worms.

Let’s take a closer look

at one worm group, the

annelids (AN-uh-lids).

Earthworms have

a long, soft body.

As they dig and eat

dirt, they make holes

in the ground. The holes help air

get into the soil, which helps plants

grow. A leech is another annelid.

It feeds on blood. Earthworms,

leeches, and other annelids move

in waves.

The body of an earthworm is made up of many segments.

snail

one shell

9

Sponges

Poriferans

Sponges are invertebrates not quite

like the others. Their bodies have only

one kind of cell and no symmetry.

A young sponge can swim. But an

adult sponge stays in one spot.

A sponge takes food from water. The

water enters tiny holes, called pores,

in the sponge. That is why this group

is called Porifera (puh-RIF-uh-ruh).

10

Sea Jellies, Corals,

and Sea Anemones

Cnidarians

Cnidarians (ny-DARE-ee-uns) have

stinging tentacles. Sea jellies, corals,

and sea anemones are in this group.

Sea jellies may also be called jellyfish,

but they are not fish. Remember,

fish are vertebrates. Sea jellies are

shaped like umbrellas. They catch

food from the water with their very

long tentacles.

A box jelly is deadly. Its poison is stronger than a cobra’s. Humans can die from a box jelly sting within a few minutes.a sponge on the seafloor

9

Sponges

Poriferans

Sponges are invertebrates not quite

like the others. Their bodies have only

one kind of cell and no symmetry.

A young sponge can swim. But an

adult sponge stays in one spot.

A sponge takes food from water. The

water enters tiny holes, called pores,

in the sponge. That is why this group

is called Porifera (puh-RIF-uh-ruh).

10

Sea Jellies, Corals,

and Sea Anemones

Cnidarians

Cnidarians (ny-DARE-ee-uns) have

stinging tentacles. Sea jellies, corals,

and sea anemones are in this group.

Sea jellies may also be called jellyfish,

but they are not fish. Remember,

fish are vertebrates. Sea jellies are

shaped like umbrellas. They catch

food from the water with their very

long tentacles.

A box jelly is deadly. Its poison is stronger than a cobra’s. Humans can die from a box jelly sting within a few minutes.a sponge on the seafloor

I am a mollusk with two shells and one foot. I can turn a grain of sand into a pearl. Who am I?

oyster

16

Not all mollusks are fast. Land snails

and slugs are slow. They make slime

to help them slide. Snails and slugs

have a special tool in their mouth

that helps

them eat as

they move.

Snails have one shell. But mollusks

called bivalves have two. Oysters

and clams are in this second group.

Some bivalves swim by clapping

their shells. Most of them eat food

from water that passes through

their gills.

15

Worms

Annelids

Worms are invertebrates,

too. There are many

different groups of worms.

Let’s take a closer look

at one worm group, the

annelids (AN-uh-lids).

Earthworms have

a long, soft body.

As they dig and eat

dirt, they make holes

in the ground. The holes help air

get into the soil, which helps plants

grow. A leech is another annelid.

It feeds on blood. Earthworms,

leeches, and other annelids move

in waves.

The body of an earthworm is made up of many segments.

snail

one shell

13 14

Most of these animals have a body

with five parts that look alike. You

can see these parts in the sand dollar

on page 12.

Sea stars (or starfish) like to

eat clams. Their strong arms pull

open the shells to get the clam meat.

Sea stars can live in tide pools or in

deep water. They can also live in very

cold water or near hot water vents

on the ocean floor.

Octopuses, Squids,

Snails, and Clams

Mollusks

Mollusks (MAW-lusks) have a

strong body. They may live in water

or on land. Some mollusks, such

as octopuses, have a soft body

covering. Others have a hard shell.

Octopuses have eight arms. They

use them to catch fish and shrimp

for food. They are also very smart.

Octopuses

and squids

swim fast

by shooting

water from

their body.

Sea stars can grow back an arm that has been lost.

Sea stars and other echinoderms can live in tide pools.

this octopus is opening a jar.

sand dollar

sea urchin

Sea Urchins, Sea Stars,

and Sand Dollars

Echinoderms

Echinoderms (ih-KY-nuh-derms)

are ocean invertebrates that have

rough skin. Sea urchins, sea stars,

and sand dollars are

in this group.

Echinoderms have

tiny feet that help

them crawl and eat.

Sea urchins look like pincushions.

They have a round body with long,

sharp spikes. Some

sea urchins eat tiny

green plants. Others

eat tiny animals.

Corals also use tentacles to catch

food. These tiny invertebrates live

close together. A group of them can

grow very large. A piece of coral

sometimes looks like a rock.

A sea anemone uses a kind of foot

to stay in one place. Around its

mouth are many tentacles that

wave in the water to catch food.

11 12

Sea anemones and clown fish rely on each other. The anemone’s stinging tentacles do not harm the clown fish. So the fish can hide there and stay safe from danger. In return, the clown fish helps keep the sea anemone clean.

sand dollar

sea urchin

Sea Urchins, Sea Stars,

and Sand Dollars

Echinoderms

Echinoderms (ih-KY-nuh-derms)

are ocean invertebrates that have

rough skin. Sea urchins, sea stars,

and sand dollars are

in this group.

Echinoderms have

tiny feet that help

them crawl and eat.

Sea urchins look like pincushions.

They have a round body with long,

sharp spikes. Some

sea urchins eat tiny

green plants. Others

eat tiny animals.

Corals also use tentacles to catch

food. These tiny invertebrates live

close together. A group of them can

grow very large. A piece of coral

sometimes looks like a rock.

A sea anemone uses a kind of foot

to stay in one place. Around its

mouth are many tentacles that

wave in the water to catch food.

11 12

Sea anemones and clown fish rely on each other. The anemone’s stinging tentacles do not harm the clown fish. So the fish can hide there and stay safe from danger. In return, the clown fish helps keep the sea anemone clean.

13 14

Most of these animals have a body

with five parts that look alike. You

can see these parts in the sand dollar

on page 12.

Sea stars (or starfish) like to

eat clams. Their strong arms pull

open the shells to get the clam meat.

Sea stars can live in tide pools or in

deep water. They can also live in very

cold water or near hot water vents

on the ocean floor.

Octopuses, Squids,

Snails, and Clams

Mollusks

Mollusks (MAW-lusks) have a

strong body. They may live in water

or on land. Some mollusks, such

as octopuses, have a soft body

covering. Others have a hard shell.

Octopuses have eight arms. They

use them to catch fish and shrimp

for food. They are also very smart.

Octopuses

and squids

swim fast

by shooting

water from

their body.

Sea stars can grow back an arm that has been lost.

Sea stars and other echinoderms can live in tide pools.

this octopus is opening a jar.