CHAPTER CHAPTER 39 39 FISHES Using the Figure Whale Shark Ask students to examine the whale shark and com- pare it to the diver in the photo. The whale shark is the largest shark species. Ask them to iden- tify the adaptations the shark has developed for life in the water which the diver does not possess. (streamlined body, fins and a tail, and gills for breathing). LS Visual

Assessing Prior Knowledge GENERAL Review the following concepts with students. Classification (Ch. 17): Remind students that, as they learned in Chapter 17, classification systems are always changing. Classification of fishes has changed and may not match older classification names that students are more familiar with. Have students review the types of data scientists use to classify animals and propose a reason the classification of fishes might have changed. (Systematists use data about physical features, The whale shark lives in a saltwater embryos, genes in the nucleus, mito- environment, for which it has special organs and biochemical adaptations. chondrial DNA, and ribosomal RNA. The whale shark is the largest fish, New information about relationships growing up to 46 feet long. Notice the size of the whale shark compared among fishes may have caused them to to the diver above. be grouped differently.) Diffusion (Ch. 5): Ask students to describe an isotonic solution, a hypotonic solution, and a hyper- SECTION 1 Introduction to Vertebrates tonic solution. (A cell containing 1% salt is placed in 1% saltwater. The SECTION 2 Jawless and Cartilaginous Fishes solutions inside and outside of the cell SECTION 3 Bony Fishes are isotonic, or equal. No net diffusion occurs. If the same cell were placed in 3% saltwater, it would be in a hypertonic 778 solution. The cell cytoplasm would be hypotonic. Water always diffuses from a Standards Correlations hypotonic solution to a hypertonic solution.) National Science Education Standards LSBeh1 Multicellular animals have nervous s ystems that generate behavior. LSEvol1 Species evolve over time. LSBeh2 Organisms have behavioral responses to internal LSEvol2 The great diversit y of organisms is the result of changes and to external stimuli. more than 3. 5 billion years of evolution. UCP5 Form and function LSEvol5 Biological classifications are based on ho w organisms are related. SI1 Abilities necessar y to do scientific inquir y LSMat4 The complexit y and organization of organisms SI2 Understandings about scientific inquir y accommodates the need for obtaining, transforming, transporting, releasing, and eliminating the matter and energ y used to sustain the organism.

778 CHAPTER 39 SECTION 1 SECTION 1 INTRODUCTION TO OBJECTIVES G Identify the distinguishing Focus VERTEBRATES characteristics of vertebrates. G List an example for each of the nine Overview classes of vertebrates. Altho ugh the vertebrates are not the most diverse or n umero us G Describe the characteristics of the Before beginning this section, early vertebrates. review with students the gro up of animals, they are the most familiar to us. Vertebrates G Explain the importance of jaws and Objectives listed in the Student are an important part of o ur diet, and many are pets. paired fins for fishes. Edition. This section describes VOCABULARY the anatomical structures that characterize all vertebrates. CHARA CTE RISTICS vertebrae It describes the classification cranium of modern vertebrates into Members of the subphylum Vertebrata, within the phylum Chordata gill arches nine classes, and the origin of (kawr-DAY-tuh) have, at some stage of life, a notochord (a rod -shaped jaws and paired fins in fishes. supporting a xis below the nerve cord), a dorsal hollow nerve cord, pharyngeal pouches (paired structures in the throat region), and a post -anal tail (a tail that e xtends beyond the anus). Vertebrates Bellringer GENERAL - have three characteristics that distinguish them from other chor Show students photos of a crab, dates. First, vertebrates have vertebrae (singular, vertebra ), bones shrimp, snail, and turtle. Even or cartilage that surround the dorsal nerve cord and form the spine. though these animals all have Second, vertebrates have a cranium, or skull, that protects the shells, ask students how the brain. Third, all vertebrates have an endoskeleton (an internal Word Roots and Origins skeleton) composed of bone or cartilage. turtle is quite different from the vertebra other three animals. (The turtle is a Vertebrate Classes vertebrate, having an internal backbone from the Latin vertebra, Today, there are about 45,000 species of vertebrates. They occupy meaning “a joint” in addition to its outer shell.) LS Visual all but the most e xtreme terrestrial habitats. The nine classes of vertebrates are summarized below. • Hagfishes (class My xini)—These fishes have elongated, eel -like bodies. They lack jaws, paired fins, and bone. The notochord Motivate remains throughout life. Hagfishes do not have vertebrae. Many scientists do not consider them vertebrates. They are included Discussion GENERAL with vertebrates because they do have a cranium and an Fish or Not Write the following endoskeleton. words on the board: starfish, sea • Lampreys (class Cephalaspidomorphi)—Lampreys lack jaws, horse, sea cow, lamprey, eel, and paired fins and bone, and retain a notochord throughout life. stingray. Ask students to identify However, unlike hagfishes, lampreys have a primitive vertebral www.scilinks.org column composed of cartilage that surrounds the notochord. which organisms they think are Topic : Fishes fish. (The starfish is not a fish, it is an • Sharks, Rays, Skates, and Ratfishes (class Chondrichthyes)— Keyw or d: HM605 79 These predatory fishes have jaws and paired fins. Their skeleton echinoderm. The sea cow is a mammal, is made of cartilage, not bone, and many have skin covered by a not a fish. The sea horse, lamprey, eel, unique kind of scale. and stingray are all fish. This demon- • Ray-finned Fishes (class Actinopterygii)—Most familiar fishes strates that fishes are a very diverse are ray -finned fishes. All have jaws and paired fins, most have a group of organisms that all share impor- skeleton composed of bone. These fish have fins supported by tant characteristics the students will rays of bone that fan out from a central bony a xis. learn about in this chapter.) LS Verbal

779 READING SKILL STATE RESOURCES TEACHER RESOURCES BUILDER Interactive Reading Assign For specific resources Workbooks for your state, visit Chapter 39 of the Modern go.hr w. co m and type in Active R eading Gu ide (S ec tio n 1) Biology Guided Reading Audio the keyword HSHS TR. CD Program to help students achieve greater success in reading the chapter. LS Verbal

FISHES 779 Class Myxini JAWLESS FISHES (hagfishes) Ancestral chordate Class Teach Cephalaspidomorphi (lampreys) Qu ic k Lab A nsw ers Class Chondrichthyes Analyzing a Phylogenetic Tree (sharks, skates, rays, and ratfishes) Time Required 20 minutes

Class BONY FISHES Procedural Tips Have students Actinopterygii work in pairs. Refer students (ray-finned fishes) to Chapter 17 for a review of FIGURE 3 9-1 Class Sarcopterygii

(lobe-finned fishes) VERTEBRATES phylogenetic trees. This phylogenetic diagram shows Ans wers to Anal ysis All vertebrates hypotheses of the evolutionary relationships among the many have a cranium, an endoskeleton, and diverse groups of chordates. For Class Amphibia vertebrae that form a spine. The devel- updates on phylogenetic information, (frogs, toads, and salamanders) opment of bone separates the class visit go.hrw.com and enter the keyword HM6 Phylo. Chondrichthyes from Actinopterygii. Class Reptilia Mammals have hair and nurse their (lizards, snakes, young with milk. and turtles)

Class Aves READING ic (birds) SKILL Qu k Lab BUILDER Analyzing a Class Mammalia K-W-L Before students read this (mammals) Phylogenetic Tree chapter, have them make short Materials paper, pencil lists of all the things they already • Lobe -f inned F is hes (class Sarcopterygii)—These fishes have fins Know about fish. When students Procedure 1. Draw the phylogenetic tree that are supported by a main a xis of bone. There are two living finish their lists, ask them to con- shown on this page on your groups of lobe-finned fishes : lungfishes and the coelacanth. tribute their entries to a class list paper. Ex tinct lobe-finned fishes are thought to be the ancestors of on the board or overhead. Then, 2. Using the information on amphibians. have students list things they pp. 779 and 780, determine the • Am ph ibians (class Amphibia)—About 4,88 0 species of frogs, key characteristics that distin- toads, and salamanders belong to this group. Their skin is thin Want to know about fish. Have guish each vertebrate group. students save their lists for use at Indicate these evolutionary and is permeable to gases and water. Most species lay their eggs the end of the chapter. changes on the branches of the in water and pass through an a quatic larval stage. tree to make a diagram of the • Re pti les (class Reptilia)—This group includes turtles, croco- relationship that exists among diles, alligators, li zards, and snakes. The skin of reptiles is dry vertebrates. Begin at the bottom and scaly. The eggs of reptiles protect the embryo from drying TEACHER RESOURCES of the tree with the key charac- out and can be laid on land. There are about 8, 000 species. teristics that distinguish verte- • Birds (class Aves)—Birds are characteri zed by adaptations that brates from other chordates. Workbooks enable flight, including feathers, hollow bones, and a uni que res- Analysis Which characteristics piratory system. There are over 1 0,000 species. Datasheets for In-Text Labs are shared by all vertebrates? Which • Mamma ls (class Mammalia)—Humans, cats, mice, and horses • Analyzing a Phylogenetic key characteristic separates the Tree classes Chondrichthyes and are among the members of this group. All mammals have hair and nurse their young with milk. There are about 4,4 00 species. Quick, Data, and Math Labs Actinopterygii? Which adaptations led to the divergence of mammals? Figure 39 -1 shows the relationships among the nine classes of liv- • Using Timelines and ing vertebrates. Phylogenetic Trees Technology 780 Transparencies • I1 Evolutionary Relationships TECHNOLOGY INCLUSION Among Chordates CONNECTION Strategies The First Vertebrates How vertebrates • Gifted and Talented first evolved from invertebrates is a ques- Students who are gifted and talented ben- tion that scientists have studied for the efit from opportunities to learn beyond past two centuries. Advances in genetic the confines of the classroom and to technology have helped scientists learn expand their classroom learning to the that a doubling in the gene composition of world around them. Ask students to an Amphioxus-like invertebrate may have research and prepare written reports on produced the first vertebrate. The scien- one or more of the e xtinct groups of fishes, tists think that this kind of sudden genetic such as the ostracoderms and placoderms. expansion could have been caused by Students should describe the structural random mutation. and behavioral characteristics of these fishes and offer possible reasons for their extinction.

780 CHAPTER 39 VERTEBRATE EVOLUTION SKILL BUILDER GENERAL Most biologists think that vertebrates originated about 560 million years ago, shortly after the first chordates appear in the fossil Interpreting Visuals Instruct stu- record. The oldest known vertebrate fossils are those of tadpole- dents to examine Figure 39-3 and like jawless fishes. They appear in the fossil record about 560 mil- explain what the diagrams are lion years ago. Figure 39 -2 shows an artist’s reconstruction of one depicting. (A model of the evolution of of these fishes. Jawless fishes were the only vertebrates for more a gill arch into a jaw.) LS Visual than 50 million years. The survivors became the ancestors of 9 today’s jawless fishes. FIGURE 3 -2 Early jawless fishes, such as this Origin of J aws and Pa ire d Fins Pharyngolepis, lacked paired fins and probably fed on small invertebrates. Close Almost 450 million years ago, the first fishes with jaws and paired Most species of early jawless fishes fins appeared. Paired fins increased fishes’ stability and maneuver- were less than 15 cm (6 in.) in length. Reteaching ability, and jaws allowed them to sei ze and manipulate prey. Jaws Chart of Vertebrates Have stu- are thought to have evolved from the first pair of gill arche s, the skeletal elements that support the pharynx. Figure 39 -3 shows dents make a chart listing the FIGURE 3 9-3 three possible stages in this transformation. Modern fishes—the nine classes of vertebrates in one Jaws are thought to have developed column, a few traits of each class sharks and rays and the bony fishes—make their first appearance from the anterior gill arches of early in the fossil record about 400 million years ago. jawless fishes. These figures represent in a second column, and hypothesized stages of evolution. an example of an animal from each class in the third column. Skull LS Logical

Quiz GENERAL True or False: 1. All adult vertebrates have Gill arch Gill slit a notochord. (false, all vertebrate embryos have a notochord, most Skull Jaws adult vertebrates do not) 2. Four of the vertebrate classes are fishes. (true) 3. Early fishes were jawless fishes. (true) SECTION 1 REVIEW TEACHER RESOURCES 1. List three distinguishing characteristics of CRITICAL THINKING Technology vertebrates. 5. Analyzing Information Why is it important to 2. List the nine classes of vertebrates, using both use unique characteristics to classify animals? Transparencies • I2 Evolution of Jaws their scientific and common names. 6. Applying Information Explain why early jaw- 3. State the characteristics of early jawless fishes. less fishes might have been awkward swimmers. Visual Concepts CD-ROM 4. Identify the advantages for fish of having jaws 7. Recognizing Relationships Explain why • Origin of Jaws, Advantage of and paired fins over not having these structures. scientists think that vertebrates evolved from Paired Fins chordates in the sea.

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Answers to Section Review 5. Answers may vary. Animals may have similar 1. They have vertebrae, a cranium, and an characteristics due to the same adaptations to endoskeleton of bone or cartilage. similar environments or due to shared ancestry. 2. Hagfishes (Myxini); Lampreys (Cephalaspidomorphi); Thus, it is important to look at unique characters Sharks, Rays, Skates, and Ratfishes (Chondrichthyes); for classification. 6. Ray-finned Fishes (Actinopterygii); Lobe-finned Answers may vary. They were probably awkward Fishes (Sarcopterygii); Amphibians (Amphibia); swimmers because they had no paired fins, which Reptiles (Reptilia); Birds (Aves); Mammals stabilize fish during swimming. (Mammalia) 7. Answers may vary. The oldest known vertebrate 3. Early fishes did not have jaws or paired fins, and fossils are those of jawless fishes. Almost all jaw- most were shorter than 15 cm in length. less fishes today are marine, as are the closest 4. Jaws afford fish a much greater ability to capture chordate relatives to vertebrates. prey, and paired fins allow for greater stability in water and more maneuverability for escaping predators or capturing prey.

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