SECTION

23.1

ANIMAL CHARACTERISTICS

Study Guide

Animals are diverse but share common characteristics.

MAIN IDEA:

CHAPTER 23 Invertebrate Diversity

KEY CONCEPT

VOCABULARY collagen homeotic homeobox

Animals are the most physically diverse kingdom of organisms.

1. Give three examples that support the statement that animals are a remarkably diverse

group of organisms.

MAIN IDEA:

All animals share a common set of characteristics.

2. Complete the following main idea web with details about the common characteristics

Copyright © McDougal Littell/Houghton Mifflin Company.

shared by all animals.

Animal characteristics

Unit 8 Resource Book McDougal Littell Biology

Study Guide

1

CHAPTER 23 Invertebrate Diversity

STUDY GUIDE, CONTINUED 3. How are animal cells different from plant cells?

4. Explain how Hox genes influence animal development.

Vocabulary Check 5. What is collagen?

6. What is the connection between homeotic and homeobox (Hox) genes?

Be Creative Copyright © McDougal Littell/Houghton Mifflin Company.

7. In the box below, design a poster that celebrates animal diversity.

2

Study Guide

Unit 8 Resource Book McDougal Littell Biology

SECTION

23.1

ANIMAL CHARACTERISTICS

Power Notes CHAPTER 23 Invertebrate Diversity

Multicellular heterotrophs:

Collagen:

Animal Characteristics Hox genes:

Copyright © McDougal Littell/Houghton Mifflin Company.

Diploid / sexual reproduction:

Unit 8 Resource Book McDougal Littell Biology

Power Notes

3

SECTION

CHAPTER 23 Invertebrate Diversity

23.1

ANIMAL CHARACTERISTICS

Reinforcement

KEY CONCEPT Animals are diverse but share common characteristics. Animals are an amazingly diverse group of organisms. They vary greatly in size and shape. They are found almost everywhere on Earth and are the dominant herbivores, predators, and detritivores in most ecosystems. Animals use a variety of methods to move, including walking, burrowing, swimming, and flying. Other animals do not move at all, and are fixed to one spot for the majority of their lives. There are four characteristics that all animals share: • All animals are multicellular heterotrophs. As you learned earlier, heterotrophs are organisms that eat other organisms to get the nutrients they need to survive. • Animal cells are supported by collagen. Collagen is a three-stranded protein unique to animals and is a component of body parts such as skin, bone, ligaments, fingernails, and hair. • Animals are diploid and usually reproduce sexually. The term diploid means that individuals have one set of chromosomes from each parent. While most animals reproduce sexually, some animals, such as whiptail lizards, reproduce asexually. • Most animals have Hox genes. Homeotic genes are a class of genes that control early development in animals. Every homeotic gene has a specific sequence of 180 nucleotides called homeobox, or Hox genes. Hox genes define the head-to-tail pattern of development in animal embryos. 1. In what ways are animals physically diverse?

Copyright © McDougal Littell/Houghton Mifflin Company.

2. List the four common characteristics that animals share.

3. What is the connection between homeotic and homeobox genes?

4

Reinforcement

Unit 8 Resource Book McDougal Littell Biology

SECTION

23.2

ANIMAL DIVERSITY

Study Guide

More than 95 percent of all animal species are invertebrates.

VOCABULARY vertebrate invertebrate phylum bilateral symmetry

CHAPTER 23 Invertebrate Diversity

KEY CONCEPT

radial symmetry protostome deuterostome

MAIN IDEA: Each animal phylum has a unique body plan. Use your textbook to fill in the missing words in the following sentences. 1. A vertebrate is an animal with an internal segmented

. Vertebrates

percent of all known animal species.

make up less than 2. Invertebrates are animals without

. Invertebrates make up over

percent of all known animal species. 3. Animals are divided into more than 30 major groups, which are called

. Each group of animals is defined by

and

characteristics. 4. Differences in body plans result from differences in the expression of

Copyright © McDougal Littell/Houghton Mifflin Company.

genes. 5. What is the function of a homeobox gene?

6. What is the connection between Hox genes and the diversity of animal body plans?

7. What factor might account for the development of so many unique body plans during

the Cambrian explosion?

Unit 8 Resource Book McDougal Littell Biology

Study Guide

5

CHAPTER 23 Invertebrate Diversity

STUDY GUIDE, CONTINUED

MAIN IDEA: Animals are grouped using a variety of criteria. For each type of symmetry, write a short description, and sketch a picture of an animal that exhibits each type of symmetry. Symmetry

Description

Sketch

8. bilateral

9. radial

10. What are three differences in the developmental patterns of protostomes and

Copyright © McDougal Littell/Houghton Mifflin Company.

deuterostomes?

Vocabulary Check 11. What is a phylum?

12. If stoma means “mouth,” what do you think proto- and deutero- mean?

6

Study Guide

Unit 8 Resource Book McDougal Littell Biology

SECTION

ANIMAL DIVERSITY

23.2

Power Notes CHAPTER 23 Invertebrate Diversity

Phylogeny of Animals

radial

Copyright © McDougal Littell/Houghton Mifflin Company.

5.

4.

3.

1.

Unit 8 Resource Book McDougal Littell Biology

6.

2.

Power Notes

7

SECTION

CHAPTER 23 Invertebrate Diversity

23.2

ANIMAL DIVERSITY

Reinforcement

KEY CONCEPT More than 95 percent of all animal species are invertebrates. A vertebrate is an animal with an internal segmented backbone. An invertebrate, on the other hand, does not have a backbone. While you may be used to seeing vertebrates such as birds, cats, or humans on a daily basis, invertebrates are actually more numerous. Scientists have divided animals into more than 30 major groups. Each group, or phylum, of animals is defined by distinctive structural and functional characteristics. There are three main criteria that are used to classify animals. These criteria include body symmetry, tissue layers, and developmental patterns. Body symmetry refers to how similar an object is across a central axis. Animals with bilateral symmetry can be divided equally along only one plane, which splits an animal into mirror-image sides. Animals with radial symmetry have body parts arranged in a circle around a central axis. Bilateral animals have three distinct layers of tissue. These layers are the ectoderm (outer layer), endoderm (inner layer that lines the gut), and mesoderm (middle layer that develops into internal tissues and organs). Most radial animals only have two layers of tissue, consisting of endoderm and ectoderm layers.

Advances in biotechnology have helped scientists use molecular comparisons along with structural differences to study the evolutionary relationships among animal groups. The phylogenetic tree, or evolutionary history, of invertebrate animals is a work in progress; as more data are gathered, a more complete evolutionary tree can be constructed. 1. What is the difference between a vertebrate and an invertebrate?

2. Does your body have bilateral or radial symmetry? Explain why.

3. What is the main difference between a protostome and a deuterostome?

8

Reinforcement

Unit 8 Resource Book McDougal Littell Biology

Copyright © McDougal Littell/Houghton Mifflin Company.

Animal developmental patterns are grouped into two major divisions: the protostomes and the deuterostomes. The major difference in development is the structure that develops from the first opening of the digestive cavity. In protostomes, the mouth is formed first and the anus is formed second. In deuterostomes, the first opening forms the anus, and the mouth is formed second.

SECTION

23.3

SPONGES AND CNIDARIANS

Study Guide

Sponges and cnidarians are the simplest animals.

VOCABULARY sessile medusa mesoglea filter feeder nematocyst polyp

CHAPTER 23 Invertebrate Diversity

KEY CONCEPT

gastrovascular cavity

MAIN IDEA: Sponges have specialized cells but no tissues. Choose the correct term or terms from the box below to complete the following sentences.

muscle nerve

sessile hard

1. Sponges lack

toxic growing and

predators parasites

cells. They are

, meaning

they are unable to move from where they are attached. 2. Sponges attach to

surfaces. They secrete

into their area and also protect them from

keep other sponges from and

substances that

.

Copyright © McDougal Littell/Houghton Mifflin Company.

3. Explain the difference between sexual and asexual reproduction in sponges.

4. How does a sponge filter feed?

5. Describe the anatomy of a sponge.

6. List and describe the three types of cells that make up a sponge.

Unit 8 Resource Book McDougal Littell Biology

Study Guide

9

CHAPTER 23 Invertebrate Diversity

STUDY GUIDE, CONTINUED

MAIN IDEA: Cnidarians are the oldest existing animals that have specialized tissues. Complete the following chart with a description and simple sketch of the two types of cnidarian body types. Body Form

Description

Sketch

7. polyp

8. medusa

9. How do cnidarians reproduce asexually?

Choose the correct term from the box to fit each definition of a part of a cnidarian’s anatomy. cnidocytes

contracting cells

mesoglea

nerve cells

animal. They send sensory information around the animal and coordinate muscular contractions. 11. This is a non-cellular jellylike material. 12. These cells cover the surface of a cnidarian and contain muscle

fibers. 13. These cells contain stinging structures used for defense and

capturing prey.

Vocabulary Check 14. What is a nematocyst?

15. What is the function of the gastrovascular cavity?

10

Study Guide

Unit 8 Resource Book McDougal Littell Biology

Copyright © McDougal Littell/Houghton Mifflin Company.

10. These cells interconnect and form a network over the entire

SECTION

23.3

SPONGES AND CNIDARIANS

Power Notes CHAPTER 23 Invertebrate Diversity

Specialized cells of a sponge:

Three types of cells that compose a cnidarian’s body:

Cnidarian Classes Description

Copyright © McDougal Littell/Houghton Mifflin Company.

Class

Unit 8 Resource Book McDougal Littell Biology

Power Notes

11

SECTION

CHAPTER 23 Invertebrate Diversity

23.3

SPONGES AND CNIDARIANS

Reinforcement

KEY CONCEPT Sponges and cnidarians are the simplest animals. Sponges are aquatic animals that have specialized cells but lack tissues. Sponges were the first animals to evolve during the Cambrian explosion. Because they lack muscle and nerve cells, sponges are sessile, which means they are unable to move from where they are attached. As a result, sponges are filter feeders, which means that they eat by straining particles from the water. Three types of specialized cells that make up a sponge’s body include • pinacocytes, which are thin and leathery cells that form the sponge’s outer layer • choanocytes, which form the inner layer of the sponge • amoebocytes, which are mobile cells found in the jellylike material that is sandwiched between the other two cell layers Unlike sponges, cnidarians can move. Cnidarians have two major body forms, the polyp and the medusa. The polyp form is a cylindrical tube with its mouth and tentacles facing upward. The medusa form is umbrella-shaped, with its mouth and tentacles on the underside. Cnidarians have two tissue layers separated by a non-cellular jellylike material called mesoglea.

A cnidarian has a gastrovascular cavity, which is a saclike digestive space. Any food that is taken in is digested within this cavity, nutrients are absorbed, and any waste is expelled through the mouth, since a cnidarian does not have an anus. 1. Both sponges and cnidarians are simple animals. What is the main difference between

the two in terms of body composition?

2. What does the term sessile mean?

3. What are the two main body forms of a cnidarian?

4. Where is food digested in a cnidarian?

12

Reinforcement

Unit 8 Resource Book McDougal Littell Biology

Copyright © McDougal Littell/Houghton Mifflin Company.

The outer tissue layer of cnidarians is made up of three types of cells: contracting cells, which cover the surface of the cnidarian and contain muscle fibers; nerve cells, which interconnect and form a network over the entire animal; and cnidocytes, which are specialized cells that contain stinging structures for defense and capturing prey. A nematocyst is a stinging structure that is made up of a capsule that contains a thin, coiled tubule with a poisonous barb at one end.

SECTION

23.4

FLATWORMS, MOLLUSKS, AND ANNELIDS

Study Guide

Flatworms, mollusks, and annelids belong to closely related phyla.

MAIN IDEA:

VOCABULARY complete digestive tract radula

hemocoel segmentation

coelom

CHAPTER 23 Invertebrate Diversity

KEY CONCEPT

Flatworms are simple bilateral animals.

1. Flatworms, mollusks, and annelids are members of which phylum?

2. Describe the basic body plan of a flatworm.

3. Why are flatworms flat?

4. What are the three classes of flatworms?

Copyright © McDougal Littell/Houghton Mifflin Company.

5. What is schistosomiasis?

6. Describe the life cycle of a tapeworm.

Unit 8 Resource Book McDougal Littell Biology

Study Guide

13

CHAPTER 23 Invertebrate Diversity

STUDY GUIDE, CONTINUED

MAIN IDEA:

Mollusks are diverse animals.

7. What is a complete digestive tract?

8. What is a benefit of having a complete digestive tract?

9. Complete the following chart with a description of each of the three shared anatomical

features of mollusks. Anatomical Feature

Description

radula

mantle

ctenidia

MAIN IDEA:

Annelids have segmented bodies.

11. What are the three groups of annelids?

Vocabulary Check 12. The word coelom comes from a Greek word that means “cavity.” How does this word

origin relate to the definition of a coelom?

14

Study Guide

Unit 8 Resource Book McDougal Littell Biology

Copyright © McDougal Littell/Houghton Mifflin Company.

10. What is a hemocoel?

SECTION

23.4

FLATWORMS, MOLLUSKS, AND ANNELIDS

Power Notes Groups / Classes

CHAPTER 23 Invertebrate Diversity

Phylum

Phylum Features

Flatworm

Copyright © McDougal Littell/Houghton Mifflin Company.

Mollusk

Annelid

Unit 8 Resource Book McDougal Littell Biology

Power Notes

15

SECTION

CHAPTER 23 Invertebrate Diversity

23.4

FLATWORMS, MOLLUSKS, AND ANNELIDS

Reinforcement

KEY CONCEPT Flatworms, mollusks, and annelids belong to closely related phyla. Most flatworms, mollusks, and annelids are classified together as members of the Lophotrochozoa. Animals in this group either have a feeding structure made of hollow tentacles called a lophophore, or a distinctive free-swimming larva called a trochophore. Flatworms are simple bilateral animals. They have a solid body that has an incomplete or absent gut. A flatworm is flat in shape because it does not have a circulatory system. This means that flatworms can only move oxygen to their cells by diffusion, so all their cells must be close to the outside environment. The three classes of flatworms include planarians, flukes, and tapeworms. While flatworms have a digestive sac with only one opening, mollusks and all other bilateral animals have a complete digestive tract. A complete digestive tract has two openings, a mouth and an anus, one at each end of a continuous tube. Mollusks share at least one feature in common: • a radula, which is a filelike feeding organ • a mantle, which is an area of tissue covering the internal organs • ctenidia, which are flat gills located in the mantle cavity Common mollusks include snails, bivalves such as clams, and squid.

Copyright © McDougal Littell/Houghton Mifflin Company.

Annelids have segmented bodies. Segmentation refers to the repeated sections of an annelid’s long body that contain a complex set of body structures. Annelids have a coelom, which is fluid-filled space that is completely surrounded by muscle. The fluid-filled coelom is used to help the annelid move in its distinctive crawling motion. Three groups of annelids include earthworms, leeches, and marine worms. 1. Why are flatworms flat?

2. What are the three classes of flatworms?

3. What is a complete digestive tract?

4. What three anatomical features are common to mollusks?

5. What is segmentation?

16

Reinforcement

Unit 8 Resource Book McDougal Littell Biology

SECTION

23.5

ROUNDWORMS

Study Guide

Roundworms have bilateral symmetry and shed their outer skeleton to grow.

CHAPTER 23 Invertebrate Diversity

KEY CONCEPT

VOCABULARY cuticle pseudocoelom

MAIN IDEA: Roundworms shed their stiff outer skeleton as they grow. Use words from the box below to complete the following sentences.

bilateral chitin

cuticle diversity exoskeleton

1. Roundworms, or

nematodes numbers

protostomes shed

, are one of the most numerous kinds of animals, and in terms of species

both in terms of 2. Members of the Ecdysozoa are

mouth-first) and they have 3. All Ecdysozoans have a tough 4. The cuticle is made of

.

(meaning their gut cavity forms symmetry. called a

.

and must be

Copyright © McDougal Littell/Houghton Mifflin Company.

whenever the animal grows larger. 5. Describe the anatomy of a roundworm.

MAIN IDEA: Many roundworms are parasites. Complete the following chart with information about parasitic roundworms. Parasite

Where Found?

Infections Occur By:

6. hookworm

Unit 8 Resource Book McDougal Littell Biology

Study Guide

17

CHAPTER 23 Invertebrate Diversity

STUDY GUIDE, CONTINUED

Parasite

Where Found?

Infections Occur By:

7. pinworm

8. Guinea worm

Vocabulary Check 9. The prefix pseudo- comes from a Greek word which means “false.” For example, the

term pseudoscience refers to a theory, method, or practice that is considered to lack a foundation in scientific principles; it is false science. How does the meaning of pseudo relate to the definition of a pseudocoelom?

Be Creative

Copyright © McDougal Littell/Houghton Mifflin Company.

Design a poster that tells people how to avoid parasitic roundworm infections. Your design can focus on just one type of roundworm or more if you choose.

18

Study Guide

Unit 8 Resource Book McDougal Littell Biology

SECTION

23.5

ROUNDWORMS

Power Notes CHAPTER 23 Invertebrate Diversity

Roundworm Characteristics

Roundworm Parasites Description

Copyright © McDougal Littell/Houghton Mifflin Company.

Parasite

Unit 8 Resource Book McDougal Littell Biology

Power Notes

19

SECTION

CHAPTER 23 Invertebrate Diversity

23.5

ROUNDWORMS

Reinforcement

KEY CONCEPT Roundworms have bilateral symmetry and shed their outer skeleton to grow. Roundworms are one of the most numerous kinds of animals, in terms of both the number of individuals and the number of different species. These animals belong to the Ecdysozoa, the same group as arthropods such as spiders and insects. All members of the Ecdysozoa have a tough outer skeleton called a cuticle. The cuticle is made of chitin and must be shed in order for the animal to grow larger. A roundworm is cylindrical in shape, with a blunt head and a tapered tail. Muscle within the roundworm’s body is separated from its central gut tube by a pseudocoelom. The pseudocoelom is a fluid-filled space that, unlike a true coelom, is not completely lined by muscle. Roundworms do not have a circulatory system or a respiratory system, but they do have a complete digestive system. Roundworms are parasites of almost every plant and animal species. They can cause a lot of damage to crop species and can negatively impact human health. Some common roundworms that infect humans include hookworms, pinworms, and Guinea worms. 1. What is a cuticle?

Copyright © McDougal Littell/Houghton Mifflin Company.

2. What are three roundworms that infect humans?

20

Reinforcement

Unit 8 Resource Book McDougal Littell Biology

SECTION

23.6

ECHINODERMS

Study Guide CHAPTER 23 Invertebrate Diversity

KEY CONCEPT

VOCABULARY ossicle water vascular system

Echinoderms are on the same evolutionary branch as vertebrates.

MAIN IDEA: Echinoderms have radial symmetry. Use words from the box below to complete the following sentences.

arm catch connective

flexible internal

ossicles ring canal

1. All echinoderms have an

stiff water

skeleton made up of many tiny

interlocking calcium-based plates called

.

2. The plates are joined together by a unique

tissue with adjustable stiffness. 3. This tissue lets echinoderms change their consistency, going from very

to very

in a matter of seconds.

4. A water vascular system is a series of

Copyright © McDougal Littell/Houghton Mifflin Company.

along each

-filled canals that extend

from the

surrounding the central disk. 5. What is the function of the water vascular system?

6. Describe how a sea star eats a clam.

Unit 8 Resource Book McDougal Littell Biology

Study Guide

21

CHAPTER 23 Invertebrate Diversity

STUDY GUIDE, CONTINUED

MAIN IDEA: There are five classes of Echinoderms. Complete the following chart with information about each Echinoderm class. Class

Description

Example

7. Crinoidea

8. Asteroidea

9. Ophiuriodea

10. Echinoidea

11. Holothuroidea

Vocabulary Check 12. The term ossicle comes from a Latin word meaning “bone.” How does this word origin

relate to the definition of an ossicle?

Create an informative brochure for a tide pool. Include information about all the different kinds of echinoderms a visitor would find there.

22

Study Guide

Unit 8 Resource Book McDougal Littell Biology

Copyright © McDougal Littell/Houghton Mifflin Company.

Be Creative

SECTION

23.6

ECHINODERMS

Power Notes CHAPTER 23 Invertebrate Diversity

Echinoderm Characteristics Symmetry:

Internal skeleton:

Water vascular system:

Digestive system: Reproduction:

Copyright © McDougal Littell/Houghton Mifflin Company.

Five Classes of Echinoderms

Unit 8 Resource Book McDougal Littell Biology

Power Notes

23

SECTION

CHAPTER 23 Invertebrate Diversity

23.6

ECHINODERMS

Reinforcement

KEY CONCEPT Echinoderms are on the same evolutionary branch as vertebrates. Adult echinoderms are radially symmetrical, although they are bilaterally symmetrical as larvae. This suggests that echinoderms had bilateral ancestors and that radial symmetry is a derived character. All echinoderms have an internal skeleton made up of many tiny interlocking calcium-based plates called ossicles. The plates are joined together by a unique catch connective tissue that has an adjustable stiffness. This tissue allows echinoderms to change their consistency, from very flexible to very stiff, in a very short time period. Echinoderms also have a water vascular system, which is a series of water-filled canals that extend along each arm. The canals store water that is used for circulation as well as for filling tiny suckerlike appendages along an echinoderm’s arms called tube feet. These tube feet are used to move around and grab objects. Echinoderms are able to regenerate portions of their body such as arms, and in some cases, even internal organs such as a portion of the digestion system. There are five classes of Echinoderms: • Crinoidea (feather stars and sea lilies) • Asteroidea (sea stars) • Ophiuroidea (brittle stars and basket stars) • Echinoide (sea urchins, sea biscuits, and sand dollars) • Holothuroidea (sea cucumbers) 1. You find an echinoderm in a tide pool that has radial symmetry. Is it an adult or a Copyright © McDougal Littell/Houghton Mifflin Company.

larva? Explain how you know.

2. What is an ossicle?

3. What are two functions of the water vascular system?

4. What might be a benefit of being able to regenerate limbs?

5. What are the five classes of Echinoderms?

24

Reinforcement

Unit 8 Resource Book McDougal Littell Biology

CHAPTER

23

INTERPRETING SCATTERPLOTS

Data Analysis Practice

GRAPH 1. DISTRIBUTION OF LAKE TROUT IN MAINE

Elevation (ft)

3000

CHAPTER 23 Invertebrate Diversity

The scatterplot below shows the distribution of lake trout based on the area and elevation of lakes throughout Maine.

2000

1000

0

1

10

100

1000

10000

Area (acres)

Copyright © McDougal Littell/Houghton Mifflin Company.

1. Describe Describe the distribution of lake trout throughout lakes in Maine.

2. Hypothesize Form a testable hypothesis that explains why there are no lake trout in

lakes smaller than 10 acres in size.

Unit 8 Resource Book McDougal Littell Biology

Data Analysis Practice

25

CHAPTER

23

NEMATOCYSTS IN ACTION

Pre-AP* Activity CHAPTER 23 Invertebrate Diversity

*Pre-AP is a registered trademark of the College Board, which was not involved in the production of and does not endorse this product. As you have learned in Chapter 23, cnidarians are armed with cnidocytes, specialized cells that help them capture prey and ward off predators. There are several types of stinging organelles found in the cnidocytes of cnidarians, but the most common is the nematocyst, like the one shown on page 708. There are at least 25 known types of nematocysts, all of which can be categorized into four groups: • piercing nematocysts that inject toxin into prey or predator • nematocysts that are used to grip surfaces to aid with locomotion • nematocysts that ensnare prey • nematocysts that are used solely for defense

While the nematocysts of most cnidarians do not pose a serious threat to humans, the northern Australian box jellyfish, Chironex fleckeri, has killed approximately one hundred people in the last century. These large cnidarians have many tentacles that can grow as long as 3 meters, and all of them bear thousands of nematocysts. These animals are found near the shore during the Australian summer (November through May), and swimmers can easily find themselves in contact with their long tentacles before they realize what’s happening. If enough nematocysts fire and enough toxin is delivered to the bloodstream of the victim, cardiac arrest can occur within minutes. Dousing the victim’s wounds with vinegar can prevent other nematocysts from firing, but it does not neutralize the venom that has already been injected into the victim.

Copyright © McDougal Littell/Houghton Mifflin Company.

THE MECHANICS OF A NEMATOCYST

By using high-speed film, scientists have been able to document the firing action of the nematocysts of Hydra. The stimulus that sets off the action appears to be the contact between the cnidocil––a small, hairlike structure that sticks out from the surface of the cnidocyte––and a predator or prey. Mechanical stimulation of the cnidocil sends an electrical signal through the cnidocyte that causes calcium ions to flood into the fluid-filled capsule surrounding the nematocyst. Water then rushes into the capsule, greatly increasing its hydrostatic pressure. This pressure forces open the operculum, a flap-like door between the nematocyst and the outside, and also forces the nematocyst outward. The long, coiled nematocyst everts, or is turned inside out, revealing sharp barbs called stylets that pierce the cuticle or skin of the organism that came into contact with the cnidocil. The barbs fold out and down like the petals of a blossoming flower, anchoring the nematocyst in the prey as the long thread unfurls and releases toxin inside. The rapid build-up of pressure inside the capsule appears to be the primary source of the nematocyst’s explosive power, but scientists think that the thread itself possesses some spring-like energy that is released when zinc is stripped from it during eversion. But does every cnidocyte need to be mechanically triggered in order for its nematocyst to fire? Biologists who study nematocysts have shown through experimentation that nematocysts will fire if they receive an electrical signal from other cnidocytes that have fired their nematocysts. In other words, when one nematocyst fires it is likely that others on the same tentacle will fire as well. This means that when a predator or prey item comes in contact

Unit 8 Resource Book McDougal Littell Biology

Pre-AP* Activity

27

CHAPTER 23 Invertebrate Diversity

with a cnidarian it will be stung more quickly by more nematocysts, because many will be set off even though only some are physically stimulated into action. The act of firing nematocysts is not without its costs. They can be fired only once, which means that a cnidarian must constantly produce new ones. For example, a Hydra uses up a quarter of its nematocysts when capturing and eating a brine shrimp, and it will take about two days to replace them. Look at the following illustration showing the firing sequence of a nematocyst.

prey A

B

F

D E

H

G

C

A B C D E F G H

cnidocil operculum cnidocyte capsule nematocyst coiled thread stylets (barbs) everted thread

1. Use two different colors of ink or pencil to show the direction in which calcium and

2. Where are the stylets or barbs in the second phase coming from? What two functions

do the barbs serve?

3. Vinegar can prevent nematocysts from firing. Speculate on how this might work.

28

Pre-AP* Activity

Unit 8 Resource Book McDougal Littell Biology

Copyright © McDougal Littell/Houghton Mifflin Company.

water move in relation to the nematocyst capsules in the first and second phases of the sequence shown. Explain how this movement causes the operculum to open and the nematocyst to evert.

CHAPTER

23

CONE SNAILS: NATURE’S DRUG MAKERS

Pre-AP Activity CHAPTER 23 Invertebrate Diversity

As you have learned in Chapter 23, the class Gastropoda is one of the largest mollusk classes. One particular group of gastropods, the family Conidae, is especially interesting to scientists these days. Cone snails, the common name for the members of this family, produce thousands of different types of potent neurotoxins. They use these neurotoxins as venom to paralyze and kill prey such as annelid worms, fish, and other mollusks. CONOTOXINS

As shown in the illustration below, cone snails typically lie partially underneath the sand around coral reefs or other shallow habitats in the Pacific and Indian Oceans. They can wait for prey to pass by, or they can use their long, flexible, wormlike proboscis to lure in prey such as small fish. The cone snail then shoots its harpoon-like radula tooth into the prey. The barbed tooth has a groove through which the potent “conotoxin” is pumped into the prey, paralyzing and killing it within moments. A thin cord attaches the tooth to the proboscis, and the prey is pulled into the expanding mouth of the snail.

venom

radula tooth

proboscis cord

Copyright © McDougal Littell/Houghton Mifflin Company.

cone snail shell

What interests scientists are the conotoxins. For one thing, they are very powerful. Several dozen people have been stung by cone snails, sometimes fatally. There are also many conotoxins. There are at least 500 known species of Conus, and each one manufactures many different peptides, the active molecules in conotoxins. Each peptide seems to be suited for specific types of receptors and ion channels in the tissues of prey. For example, the conotoxin of Conus geographus, one of the most dangerous species, has peptides that interfere with sodium channels, calcium channels, acetylcholine receptors, and NMDA receptors. This means that cone snails are able to paralyze prey by attacking neurological and muscular pathways. Because receptors vary from species to species, the cone snail is armed with a variety of peptides, meaning the Conidae family as a whole makes thousands of unique conotoxins. So far, scientists have been able to identify only a fraction of the receptors that these peptides affect.

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Pre-AP Activity

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CHAPTER 23 Invertebrate Diversity

FROM DEADLY CONOTOXIN TO PAIN RELIEVER

Because conotoxins bind to receptors, they block nerve signals, including those that create the sensation of pain. Already scientists have developed several painkillers by studying and synthesizing peptides of conotoxins. Prialt is a drug that relieves chronic pain in people suffering from cancer and other diseases. It is based on the conotoxin of Conus magus, the magician cone snail. Scientists estimate that there are 75,000 other peptides to be studied in the cone snail family, any number of which could lead to development of drug treatments for Parkinson’s disease, epilepsy, Alzheimer’s, and symptoms of AIDS. In 2006, a team led by researchers from the University of Utah identified a conotoxin called alpha conotoxin Om1A. This conotoxin binds to acetylcholine receptors in the nervous system that are involved in addiction, memory, involuntary movements, and even depression. The scientists think that by determining the precise shape of the receptors that the new conotoxin binds to, and using the conotoxin as a kind of mold or template, they can synthesize drugs that will target specific receptors without affecting others. This could lead to effective treatments for a variety of problems, from cigarette addiction to schizophrenia to depression. 1. How does it benefit a cone snail to be able to make many different conotoxins?

2. Many cone snails live in coral reef communities that are threatened by overfishing,

3. Fossil evidence suggests that cone snails first evolved after the Cretaceous extinction,

which wiped out the dinosaurs on land and the ammonites in the ocean. What term would you use to characterize the appearance of the many species of cone snails?

4. Cone snails cannot ingest a human. Why then would their conotoxins be fatal in humans?

What does this say about the evolution of humans, fish, annelids, and other animals?

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Pre-AP Activity

Unit 8 Resource Book McDougal Littell Biology

Copyright © McDougal Littell/Houghton Mifflin Company.

warming sea temperatures, and other human impacts, including the sea shell industry. Thinking in terms of the potential for discovering new compounds, explain how the conservation of coral reefs and cone snails is analogous to the conservation of tropical rain forests.

CHAPTER

23

INVERTEBRATE DIVERSITY

Vocabulary Practice CHAPTER 23 Invertebrate Diversity

collagen

deuterostome

radula

homeotic

sessile

hemocoel

homeobox

filter feeder

segmentation

vertebrate

polyp

coelom

invertebrate

medusa

cuticle

phylum

mesoglea

pseudocoelom

bilateral symmetry

nematocyst

ossicle

radial symmetry

gastrovascular cavity

water vascular system

protostome

complete digestive tract

A. What’s the Difference? For each pair of words below, describe the difference between the two terms. 1. bilateral symmetry/radial symmetry

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2. vertebrate/invertebrate

3. polyp/medusa

4. protostome/deuterostome

5. sessile/mobile

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Vocabulary Practice

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CHAPTER 23 Invertebrate Diversity

VOCABULARY PRACTICE, CONTINUED

B. Who Am I? Choose among these terms to answer the riddles below: collagen

homeobox

protostome

deuterostome

invertebrate

vertebrate

1. I am an animal with an internal segmented backbone: 2. I am a three-stranded protein unique to animals: 3. I am an animal without a backbone: 4. I have a developmental pattern in which the anus develops first: 5. I am a type of gene that defines the head-to-tail developmental pattern

in animal embryos: 6. I have a developmental pattern in which the mouth forms first:

filter feeder

mesoglea

radula

medusa

polyp

water vascular system

7. I eat by straining particles from the water: 8. I am a filelike feeding organ found in mollusks:

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9. I am the umbrella-shaped body form of a cnidarian: 10. I am a series of water-filled radial canals that extend along each arm of a

sea star: 11. I am the cylindrical-shaped body form of a cnidarian: 12. I am a non-cellular jelly-like material that separates the two tissue layers

of a cnidarian:

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Vocabulary Practice

Unit 8 Resource Book McDougal Littell Biology

VOCABULARY PRACTICE, CONTINUED

1. Doesn’t move

CHAPTER 23 Invertebrate Diversity

C. Secret Message Next to each definition, fill in the blanks with the vocabulary word that best fits each description. When complete, write the boxed letters in order in the blanks at the bottom of the page to discover the name of a famous zoologist.

2. Tiny interlocking plates that make up a sea

star’s skeleton

3. Animal with a backbone

4. Animal without a backbone 5. Tough exoskeleton that must be shed so a

roundworm can grow larger

6. Fluid-filled space found in a roundworm

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7. Spaces between cells within a mollusk’s

tissues 8. Major group of species defined by structure

and function 9. Class of genes that control early animal

development

10. Repeated sections of an annelid’s body

11. Cnidarian stinging structure

Fill in the blanks with the boxed letters from above to name the famous zoologist:

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Vocabulary Practice

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CHAPTER 23 Invertebrate Diversity

VOCABULARY PRACTICE, CONTINUED

D. Analogy Vocabulary Set On one blank line next to each vocabulary word, write the letter and number of the definition that best matches. On the other blank line, write the letter and number of the analogy that best matches. DEFINITIONS

WORD

D1. Type of symmetry in which

ANALOGIES

1. Cuticle

A1. Mirror-image

2. Bilateral

A2. Egg shell

an animal has body parts arranged in a circle around a central axis D2. Stinging structure

symmetry D3. Repeated sections of an

3. Radial symmetry

A3. Harpoon

4. Segmentation

A4. Spokes on a wheel

5. Nematocyst

A5. Cars on a train

annelid’s body D4. Type of symmetry in which

an animal’s body can be split evenly over one plane D5. Tough exoskeleton

coelom

mesoglea

polyp

segmentation

hemocoel

nematocyst

radula

water vascular system

medusa

ossicle Cnidarian Anatomy

Annelid Anatomy

a.

a.

b.

b.

c. d. Mollusk Anatomy

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Echinoderm Anatomy

a.

a.

b.

b.

Vocabulary Practice

Unit 8 Resource Book McDougal Littell Biology

Copyright © McDougal Littell/Houghton Mifflin Company.

E. Categorize Words List the vocabulary words that belong in each category.