11 Invertebrates-High

Invertebrates Written by Brooke Bessesen

Introduction Invertebrates are "spineless" animals. Calling them spineless doesn't mean they are always afraid. It means that invertebrates have no backbone, or spine. Run your hand down the center of your back. Do you feel all those bumps? Those are the bones of your spine, and they are called vertebrae (VER-tuh-bray). Animals that have a spine are called vertebrates. Humans are vertebrates. But most animals are invertebrates.

What Do Invertebrates Have in Common? Invertebrates come in a wide variety of shapes and sizes, yet they have a lot in common. You already know that they have no spine. Invertebrates share several other traits, too: Like vertebrates, invertebrates have more than one cell. Their cells work together to keep them alive. Each cell has a job to do. All invertebrates move in some way. Most move from one location to another. Others stay in one place but move their body parts. Invertebrates don't have lungs, so they don't breathe as we do. They get oxygen through gills or through tiny openings on their body.

Most invertebrates have symmetry. In some, the two sides of their body look just like each other. Others have a center point. If you draw any line through that center, you will have matching halves. Since invertebrates cannot make their own body heat, they are cold-blooded. Most invertebrates reproduce with sperm from the male and eggs from the female. Unlike plants, invertebrates must eat to get energy. They cannot make their own food. In this book, you will learn how some invertebrate groups move and get food. You will also learn some of their special traits.

Classifying Invertebrates Although invertebrates share many traits, each group has tremendous differences. A fruit fly is smaller than a grain of rice, but a giant squid can be 17 meters (55 ft.) long, with eyes bigger than basketballs! Centipedes eat worms, but butterflies drink nectar. A mosquito flies in the air, but a crab crawls on the seafloor. In fact, more than a million kinds of invertebrates live on Earth. Just think of all that diversity! Word Wise Each type of animal has a common name and a scientific name. Apis mellifera is the scientific name for a honeybee.

Because so many animals look and behave in different ways, scientists have grouped them. First they classify animals as either vertebrates or invertebrates. Scientists have identified about 30 invertebrate groups. Each group contains smaller subgroups. All the animals in a group have similar traits. As you read about some of these groups, try to figure out why certain invertebrates are grouped together. Vertebrates Mammals Birds Reptiles Amphibians Fish Invertebrates Poriferans sponges Cnidarians sea jellies corals sea anemones Echinoderms sea stars sea urchins sand dollars Mollusks octopuses squids snails clams Annelids earthworms Arthropods insects spiders lobsters millipedes These are the invertebrate groups covered in this book