Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
KEY CONCEPT Most animals are invertebrates. Sunshine State STANDARDS SC.F.2.3.3: The student knows that generally organisms in a population live long enough to reproduce because they have survival characteristics. SC.G.1.3.3: The student understands that the classification of living things is based on a given set of criteria and is a tool for understanding biodiversity and interrelationships. SC.H.2.3.1: The student recognizes that patterns exist within and across systems. VOCABULARY invertebrate p. 413 sponge p. 415 sessile p. 415 larva p. 416 BEFORE, you learned NOW, you will learn • Animals are consumers; they get food from the environment • Most animals have body systems, including tissues and organs • Animals interact with the environment and other animals • About the diversity of invertebrates • About six groups of invertebrates • How sponges get energy THINK ABOUT What makes an animal an animal? A sponge is an animal. It has no head, eyes, ears, arms, or legs. A sponge doesn’t have a heart or a brain or a mouth. It doesn’t move. Typically, it spends its life attached to the ocean floor. Many people used to think that sponges were plants that had adapted to life in the water. Scientists, however, classify them as animals. How might you decide if the organism in the photograph is an animal? Invertebrates are a diverse group of organisms. COMBINATION NOTES Make notes and diagrams for the first main idea: Invertebrates are a diverse group of organisms. Include a sketch of a member of each group. About one million invertebrate species live on Earth. Invertebrates are animals that do not have backbones. In fact, invertebrates do not have any bone tissue at all. Invertebrates can be found just about everywhere, from frozen tundra to tropical forests. Some invertebrates live in water, while others survive in deserts where there is almost no water. Many invertebrates live inside other organisms. Most invertebrate animals are small. Crickets, oysters, sea stars, earthworms, ants, and spiders are some examples of invertebrates. The fact that invertebrates do not have backbones for support tends to limit their size. However, some ocean-dwelling invertebrates can be quite large. For example, the giant squid can grow to 18 meters (59 ft) in length and can weigh over 450 kilograms (992 lb). Chapter 12: Invertebrate Animals 413 Invertebrates Which types of invertebrates live near you? SKILL FOCUS Observing PROCEDURE 1 Cut the potato in half lengthwise. Scoop out a hole and carve a channel so it looks like the photograph below. 2 Put the two halves back together and wrap them with masking tape. Leave the channel uncovered. It is the entrance hole. 3 Take the potato trap outside and bury it upright in soil, with the entrance hole sticking out of the ground. Wash your hands. 4 Collect the potato the next day. Remove the masking tape and look inside. MATERIALS • • • • potato knife spoon masking tape TIME 20 minutes WHAT DO YOU THINK? • Observe the contents of the potato. Record your observations. • Would you classify the contents of the potato as living or nonliving? Do you think they are animals or plants? CHALLENGE Predict how your observations would be different if you buried the potato in a different place. In this chapter, you will learn about six groups of invertebrates: are the simplest invertebrates. They live in water. They filter food from the water that surrounds them. Cnidarians also live in water. Animals in this group have a central opening surrounded by tentacles. They take in food and eliminate waste through this opening. Jellyfish, sea anemones, hydras, and corals are cnidarians. Worms are animals with soft, tube-shaped bodies and a distinct head. Some worms live inside other animals. Others live in the water or on land. Mollusks have a muscular foot that allows them to move and hunt for food. Some mollusks live on land. Others live in water. Clams, snails, and octopuses are mollusks. Echinoderms are water animals that have a central opening for taking in food. Sea stars and sand dollars are echinoderms. Arthropods are invertebrates that are found on land, in the water, and in the air. They have legs. Some have wings. Insects, spiders, crabs, and millipedes are arthropods. • Sponges • • • • • 414 Unit 3: Diversity of Living Things Sponges are simple animals. Sponges are the simplest multicellular animals on Earth. These invertebrates are sessile (SEHS-EEL) organisms, which means they live attached to one spot and do not move from place to place. Most live in the ocean, although some live in fresh water. Sponges have no tissues or organs. The body of a sponge is made up of a collection of cells. The cells are organized into a body wall, with an outside and an inside. Sponges are adapted to feed continuously. They feed on plankton and other tiny organisms that live in the water. VOCABULARY Make a description wheel for sponge. Include information on its specialized cells. Specialized Cells A sponge meets its needs with cells specialized for different functions. Pore cells along the body wall create tiny openings throughout the body. The pores lead into larger canals and sometimes a central opening, where cells with tiny hairs, or flagella, move water through the sponge. As water moves out, more water enters, as shown in the diagram below. Specialized cells filter out food particles and oxygen. Other specialized cells digest the food. Check Your Reading What adaptations does a sponge have for obtaining food? Feeding in Sponges Structures in a sponge’s body function to remove food from water. 2 Flagella along the inside of the sponge move water through the sponge. 1 Water flows into the sponge through pores in the body wall. flow of water 3 4 Specialized cells digest the food particles. inside of sponge Specialized cells pick up food particles as the water moves by. pores Chapter 12: Invertebrate Animals 415 Another adaptation sponges have are structures that make the body stiff. Most sponges have spicules (SPIHK-yoolz), which are needlelike spines made of hard minerals such as calcium or silicon. Spicules help give the sponge its shape and provide support. In some sponges, spicules stick out from the body. This may make the sponge less likely to become a source of food for other animals. Reproduction Sponges can reproduce asexually. Buds form alongside the parent sponge or the buds break off and float away. Tiny sponges can float quite a distance before they attach to the ocean floor or some underwater object and start to grow. Sponges also reproduce sexually, as most multicellular organisms do. In sponges, sperm are released into the water. In some sponges, the eggs are released too. In this case, fertilization occurs in the water. In other sponges, the eggs are contained in specialized cells in the body wall. Sperm enter the sponge to fertilize the eggs. A fertilized egg becomes a larva. A larva is an immature form—an early stage—of an organism that is different from the parent. Sponge larvae are able to swim. They move away from the parent and will grow into a sponge once they attach to some underwater surface. Then they become sessile, like their parents. This basket sponge is releasing microscopic larvae into the water. Sponges provide a good starting point for studying other invertebrates. There are many different types of invertebrates, with a wide range of body structures and behaviors. Invertebrates have adapted to many different environments. But the sponge is a simple organism that has changed very little over time. Sponges today look very similar to fossil sponges that are millions of years old. KEY CONCEPTS CRITICAL THINKING 1. Make a table with six columns. Write the name of an invertebrate group above each column. Fill in the table with a characteristic and an example for each group. 4. Apply Give two examples of how structure in a sponge relates to function. You should use the words flagella and spicule in your answer. 2. What does it mean that sponges are sessile? 3. How do sponges meet their need for energy? 416 Unit 3: Diversity of Living Things 5. Infer How is water involved in the reproductive cycle of a sponge? CHALLENGE 6. Analyze Sponges have lived on Earth for hundreds of millions of years. Sponges today look very similar to fossil sponges. What does this suggest about how well the simple structure of a sponge meets its needs? Do species always change over time?