Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Bellringer Record your answers to the following questions in your science journal: What is an invertebrate? What is your favorite invertebrate? What special features help your favorite invertebrate survive? Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Objectives Describe the body plans, nervous systems, and guts of invertebrates. Explain how sponges get food. Describe three cnidarian characteristics. Describe the three kinds of flatworms. Describe the body of a roundworm. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu An Invertebrate is an animal that does not have a backbone. About 96% of all animal species are invertebrates Invertebrates have three basic body plans, or types of symmetry: bilateral, radial, or asymmetrical. Chapter 15 Section 1 Simple Invertebrates Invertebrate Characteristics

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Invertebrate Characteristics, continued Nerves All animals except sponges have nerves. Nerves allow animals to sense their environment and control their actions. Some invertebrates have ganglia. A ganglion is a concentrated mass of nerve cells. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Invertebrate Characteristics, continued Guts Almost all animals digest food in a gut. A gut is a pouch lined with cells that release chemicals that break down food into small particles. Complex organisms have a coelom. A coelom is a body cavity that surrounds the gut. Other organs can also be found in the coelom, but they are separated from the gut. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sponges Sponges are the simplest invertebrates. They are asymmetrical and have no tissues, gut, or nerves. How Do Sponges Eat? A sponge sweeps water into its body through its pores. Pores are the holes on the outside of the sponge’s body. Collar cells filter and digest food from the water that enters the body. Water leaves through the hole at the top called the osculum. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sponges, continued Body Part Abilities Sponges have some unique abilities. If you forced a sponge’s body through a strainer, the separated cells could come back together and reform the same sponge. If a part of a sponge is broken off, the missing part can regenerate, or grow back. Sponges are the only animals that can use regeneration as a form of reproduction. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Sponges, continued Kinds of Sponges All sponges live in water, and most live in the ocean. Sponges come in many different shapes and sizes. Most sponges have a skeleton made of hard fibers called spicules. Some spicules are straight, some are curved, and others have complex star shapes. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Cnidarians Cnidarians are more complex than sponges. Cnidarians have complex tissues, a gut, and a simple nerve network. Two Body Forms A cnidarian body can either be in medusa form or polyp form. Medusas swim through the water. Polyps usually attach to a surface. Both the medusa and the polyp forms have radial symmetry. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Chapter 15 Section 1 Simple Invertebrates Body Form of Cnidarians

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Cnidarians Stinging Cells All cnidarians have tentacles covered with stinging cells. Cnidarians use their stinging cells to protect themselves and to catch food. Kinds of Cnidarians There are three major classes of cnidarians: hydrozoans, jellyfish, sea anemones and some corals. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Flatworms Flat worms have bilateral symmetry, a clearly defined head and two large eyespots. The eyespots cannot focus, but the flatworm can use them to sense the direction that light is coming from. Some flatworms also have sensory lobes that are used for detecting food. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Flatworms, continued Planarians Planarians live in freshwater lakes and streams or on land in damp places. Most planarians are predators. Flukes Flukes are parasites. A parasite is an organism that invades and feeds on the body of another living organism that is called a host. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Flatworms, continued Tapeworms Tapeworms are similar to flukes. Like flukes, they have a small head with no eyespots or sensory lobes. Tapeworms do not need a gut because they attach directly to the host’s intestines and absorb nutrients. Chapter 15 Section 1 Simple Invertebrates

Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Roundworms Roundworms have bodies that are long, slim, and round, like spaghetti. Like other worms, they have bilateral symmetry. Roundworms have a simple nervous system. A ring of ganglia forms a simple brain. Parallel nerve cords connect the two ends of their body. Some round worms eat dead tissue. Many roundworms are parasites. Chapter 15 Section 1 Simple Invertebrates