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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.