Chapter 28:  Introduction to Animals

Using your vocabulary words, make notecards/flashcards that you can use outside of class to study. 

Work on your Directed Reading in class every chance you get.  Remember that I will assist you on the harder questions.  This assignment is due the day we take the test on this chapter.  Use the information in this assignment as a study guide for your test.

This study guide is to help you study for your test.  It should not be the only item you use to study w hen preparing for the test.  Remember to complete your Directed Reading for every chapter along with writing your vocabulary words on notecards to help you remember them.  And always remember to listen carefully in lecture because all of the information in this study guide will be covered.

Introduction to Animals

The sponges and coral in the photograph are sessile—that is, they attach themselves to an object and remain in that place all their lives. Sponges create water currents that flow through their bodies and trap microorganisms found in these currents for food. Corals capture prey that swim within their reach.

* What are the advantages of being a sessile animal?

* Sponges were once classified as plants. Why do you think this was so?

An elephant, a hummingbird, and a jellyfish differ greatly in their size, shape, and behavior. Nevertheless, they are all ani­mals. In distinguishing between types of organisms, the charac­teristics animals have in common far outweigh the differences among them. However, differences in body structure are useful in classifying animals. The arrangement of body parts is re­lated to how a particular animal species meets the challenges of living, which include gathering food, protecting itself, and reproducing.

Symmetry and Body Plans

The arrangement of an animal's body parts determines its sym­metry. Most animals are symmetrical in some way. Only a few animals can be described as asymmetrical, or having an arrange­ment of body parts that cannot be divided into corresponding sections. Many sponges are asymmetrical. They grow in varied and irregular shapes.

The symmetry of an animal generally provides a clue to its way of life. An organism with a round form—with no front or back, no right or left side—shows spherical symmetry . This form is well suited to certain protozoa that roll and float in water. Such organisms face all directions at once.

Animals whose body parts are arranged around a central point, like spokes around the hub of a wheel, exhibit radial symmetry. Their sensory organs are located around the circum­ference of the body. Jellyfish and sea anemones show radial symmetry. Such animals do not move efficiently. Either they are sessile, or they float in the water or crawl along the bottom of the sea.

Most animal species have bilateral symmetry—that is, one-half of the body is a mirror image of the other half. A butter­fly is a good example of bilateral symmetry. If a line were drawn lengthwise through the butterfly's body—the longitudinal axis—the right half would appear to be the exact opposite of the left half.

Bilaterally symmetrical animals have upper and lower sur­faces, and front and hind ends. The upper surface is called the dorsal surface, and the lower surface the ventral surface. The front is the anterior end, and the hind the posterior end. For example, the backbone of a dog is dorsal, and the stomach is ventral. The head is at the anterior end, and the tail is at the pos­terior end.

Animals that have a definite anterior end and move head first generally exhibit cephalization (sehf uh lih ZAY shuhn). Cephalization is an adaptation in which the neural and sensory organs are concentrated in the anterior end in animals. When such animals move, their sensory organs go first, providing information about the environment that lies ahead of the animals.

Vertebrates and Invertebrates

Scientists make a major distinction between vertebrates, ani­mals with a backbone or a spine, and invertebrates, animals without a backbone. Humans and other mammals are verte­brates, as are fish, amphibians, reptiles, and birds. Vertebrates are included in the phylum Chordata. Although they are the most widely recognized and familiar of all animals, vertebrates make up only about 3 percent of the more than 1 million species of animals. Vertebrates are categorized by bilateral symmetry and cephalization.

About 97 percent of the animal kingdom are invertebrates. Invertebrates include sponges, jellyfish, starfish, worms, mollusks, insects, and crabs. Some species of invertebrates have radial symmetry, and some bilateral. Some, but not all, species are characterized by cephalization.

Chapter 28 Teacher Resources