Invertebrates. A Science A Z Life Series Word Count: 1,041. Invertebrates. Written by Brooke Bessesen. Visit

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1 Invertebrates A Science A Z Life Series Word Count: 1,041 Invertebrates Written by Brooke Bessesen Visit

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3 mollusks spine sponges symmetry vertebrates a group of invertebrates that have a soft, unsegmented body, and most have one or two shells; includes snails and octopuses (p. 14) a column of bones that provides the main support for a vertebrate s body; the backbone, or vertebral column (p. 4) a group of primitive marine invertebrates with a porous body that permanently attaches to a solid surface in adulthood (p. 9) the property of having the same size and shape across a dividing line, or having one half identical to the other half (p. 6) animals that have a backbone (p. 4) Invertebrates arachnids, 19 bivalves, 15 crustaceans, 20, 21 gills, Index pollinators, 18 prey, 20 symmetry, 6, 9 tentacles, 10, 11 Written by Brooke Bessesen

4 Key elements Used in This Book The 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 information Other 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 knowledge Other suitable reading strategies: Ask and answer questions; summarize; visualize; retell 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 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) Invertebrates / Learning A Z / Written by Brooke Bessesen All rights reserved. / 23

5 Table of Contents 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. 22 All humans All invertebrates Introduction... 4 What Do Invertebrates Have in Common?... 5 Classifying Invertebrates... 7 Sponges... 9 Sea Jellies, Corals, and Sea Anemones Sea Urchins, Sea Stars, and Sand Dollars Octopuses, Squids, Snails, and Clams Worms Insects, Spiders, Lobsters, and Millipedes Conclusion Glossary Index

6 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). Invertebrate Sponges Corals Sea urchins Interesting Invertebrate Information Clams, oysters, and mussels Information Nowadays, sponges used in sinks and showers are factory-made, but people used to use real sponges from the sea. Coral reefs provide shelter for many marine animals. Reefs can also protect shoreline habitats by stopping giant waves. Some sea urchins can live for over 200 years. Mollusks provide a food source for many animals, including some humans. Animals with a spine are called vertebrates. You are a vertebrate. But most animals are invertebrates. Worms Insects Doctors sometimes use leeches to bring blood into fingers that have been sewn back on. Frogs, toads, some birds, and many other animals survive on a diet mainly or entirely made up of insects. Vertebrates Invertebrates Spiders By eating so many insects, spiders help control the number of insects in the world. Crustaceans Many large marine animals eat tiny crustaceans called krill. Blue whales eat 8,000 pounds of krill a day. Millipedes Millipedes are important decomposers. They help break down dead plant life. 4 21

7 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 shrimp lobster crab as fish, mollusks, worms, and plants. 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. 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. 20 centipede milipede All invertebrates move their body in some way. Invertebrates need oxygen, but they do not breathe as we do. fly swim crawl These invertebrates have different ways of moving. 5

8 bilateral symmetry radial symmetry 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. Most invertebrates have symmetry. That means the sides of their body look alike. Invertebrates can t make their own heat. They are cold-blooded. 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. Most invertebrates make young with sperm from males and eggs from females. Invertebrates eat to stay alive. Spiders make webs to catch insects. Webs are also used as nests for young spiders. scorpion In this book, you will learn about some groups of invertebrates. You will find out how they move and eat. mite tick spider 6 19

9 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! A honeybee exploring a flower Some insects are Three stages in the life cycle of a butterfly 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. 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! Giant squids have eyes bigger than basketballs! Invertebrates can be very different from each other. 18 7

10 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. vertebrates Mammals Birds Reptiles Amphibians Fish 8 Poriferans Cnidarians Echinoderms Mollusks Annelids Arthropods invertebrates* sponges sea stars sea urchins sand dollars earthworms *These are the invertebrate groups covered in this book. sea jellies corals sea anemones octopuses squids snails clams insects spiders lobsters millipedes 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. Insect Body Parts head thorax abdomen wings two antennae six legs 17

11 16 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. 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). A sponge on the seafloor 9

12 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. 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. one shell snail 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. 10 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. I am a mollusk with two shells and one foot. I can turn a grain of sand into a pearl. Who am I? oyster 15

13 14 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. This octopus is opening a jar. 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. 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. 11

14 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 urchin sand dollar 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. 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. Sea stars and other echinoderms can live in tide pools. Sea stars can grow back an arm that has been lost