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Chapter Presentation
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Visual Concepts
Standardized Test Prep
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Chapter 34
Flatworms, Roundworms, and
Rotifers
Table of Contents
Section 1 Platyhelminthes
Section 2 Nematoda and Rotifera
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Chapter 34
Section 1 Platyhelminthes
Objectives
• Summarize the distinguishing characteristics of
flatworms.
• Describe the anatomy of a planarian.
• Compare free-living and parasitic flatworms.
• Diagram the life cycle of a fluke.
• Describe the life cycle of a tapeworm.
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Chapter 34
Section 1 Platyhelminthes
Structure and Function of Flatworms
• The phylum Platyhelminthes includes organisms called
flatworms.
• They are more complex than sponges but are the simplest
animals with bilateral symmetry.
• Their bodies develop from three germ layers:
– ectoderm
– mesoderm
– endoderm
• They are acoelomates with dorsoventrally flattened bodies.
• They exhibit cephalization.
• The classification of Platyhelminthes has undergone many
recent changes.
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Chapter 34
Section 1 Platyhelminthes
Characteristics of Flatworms
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Chapter 34
Section 1 Platyhelminthes
Class Turbellaria
• The majority of species in the class Turbellaria live in
the ocean.
• The most familiar turbellarians are the freshwater
planarians of the genus Dugesia.
• Planarians have a spade-shaped anterior end and a
tapered posterior end.
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Chapter 34
Section 1 Platyhelminthes
Class Turbellaria, continued
Digestion and Excretion in Planarians
• Planarians feed on decaying plant or animal matter
and smaller organisms.
• Food is ingested through the pharynx.
• Planarians eliminate excess water through a network
of excretory tubules.
– Each tubule is connected to several flame cells.
– The water is transported through the tubules and
excreted from pores on the body surface.
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Chapter 34
Section 1 Platyhelminthes
Class Turbellaria, continued
Neural Control in Planarians
• The planarian nervous system is more complex than
the nerve net of cnidarians.
• The cerebral ganglia serve as a simple brain.
• A planarian’s nervous system gives it the ability to
learn.
• Planarians sense light with eyespots.
• Other sensory cells respond to touch, water
currents, and chemicals in the environment.
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Chapter 34
Section 1 Platyhelminthes
Class Turbellaria, continued
Reproduction in Planarians
• Planarians are hermaphrodites that can reproduce
sexually or asexually.
• Their eggs are laid in capsules.
• During asexual reproduction, their body undergoes
fission and the two halves regenerate missing parts.
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Chapter 34
Section 1 Platyhelminthes
Planarian
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Chapter 34
Section 1 Platyhelminthes
Anatomy of a Planarian
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Chapter 34
Section 1 Platyhelminthes
Exploration of a Flatworm
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Chapter 34
Section 1 Platyhelminthes
Development of
Flatworm Embryo
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Chapter 34
Section 1 Platyhelminthes
Classes Trematoda and Monogenea
• The classes Trematoda and Monogenea consist of parasitic
flukes.
• Some are endoparasites; others are ectoparasites.
Structure of Flukes
• A fluke clings to the tissues of its host by an anterior sucker and
a ventral sucker.
• A fluke’s nervous system is similar to a planarian’s, but simpler.
• The external surface of a fluke is covered by a protective layer
called the tegument.
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Chapter 34
Section 1 Platyhelminthes
Tegument
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Chapter 34
Section 1 Platyhelminthes
Classes Trematoda and Monogenea, continued
Reproduction and Life Cycle of Flukes
• Most flukes have highly developed reproductive
systems and are hermaphroditic.
• Fertilized eggs are stored in a fluke’s uterus until they
are ready to be released.
• Flukes have complicated life cycles that involve more
than one host species.
• For example, the trematode blood flukes of the genus
Schistosoma use humans as a primary hosts and
snails as intermediate hosts. They can cause
schistosomiasis.
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Chapter 34
Section 1 Platyhelminthes
Life Cycle of
Schistosoma
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Chapter 34
Section 1 Platyhelminthes
Life Cycle of Flukes
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Chapter 34
Section 1 Platyhelminthes
Class Cestoda
• About 5,000 species of tapeworms make up the class
Cestoda.
• Tapeworms can live in the intestines of almost all
vertebrates.
Structure of Tapeworms
• Tapeworms are surrounded by a tegument.
• They attach to the host with a scolex.
• The body is a series of many sections called
proglottids.
• Tapeworms have no light-sensing organs, no mouth,
no gastrovascular cavity, and no digestive organs.
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Chapter 34
Section 1 Platyhelminthes
Anatomy of a Tapeworm
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Chapter 34
Section 1 Platyhelminthes
Class Cestoda, continued
Reproduction and Life Cycle of Tapeworms
• Nearly all tapeworms are hermaphrodites. Each proglottid
contains male and female reproductive organs and little else.
• New proglottids are added to the front of the tapeworm. Older
proglottids grow, mature, and begin producing eggs.
• Eggs in one proglottid are usually fertilized by sperm from a
different proglottid, possibly a different individual.
• An example is the beef tapeworm, Taenia saginatus. Its primary
host is a human and its intermediate host is a cow. Its larvae
form cysts in the muscle tissue of the cow.
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Chapter 34
Section 1 Platyhelminthes
Life Cycle of Beef Tapeworm
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Chapter 34
Section 1 Platyhelminthes
Life Cycle of Tapeworms
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Chapter 34
Section 2 Nematoda and Rotifera
Objectives
• Describe the body plan of a nematode.
• Outline the relationship between humans and
parasitic roundworms.
• Describe the anatomy of a rotifer.
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Chapter 34
Section 2 Nematoda and Rotifera
Phylum Nematoda
• The phylum Nematoda is made up of roundworms
with long, slender bodies that taper at both ends.
• Roundworms are among several phyla of
pseudocoelomates.
• Roundworms have a digestive tract with two
openings.
• Most roundworms have separate sexes and are
covered by a protective cuticle.
• Most species are free-living; some are parasites.
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Chapter 34
Section 2 Nematoda and Rotifera
Phylum Nematoda, continued
Ascaris
• The genus Ascaris infects pigs, horses, and humans.
• The eggs enter hosts through contaminated food or water,
develop into larvae in the intestines, and can infect the lungs.
• The eggs are spread in the hosts’ feces.
Hookworms
• Hookworms are intestinal parasites that feed on blood.
• The eggs produce larvae in soil, and the larvae enter hosts
through the feet.
• Hookworms infect about one billion people worldwide.
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Chapter 34
Section 2 Nematoda and Rotifera
Phylum Nematoda, continued
Trichinella
• The genus Trichinella infects humans and other mammals.
• Adults live in intestines and larvae form cysts in muscles.
• People usually become infected from undercooked pork.
• Infection causes the disease trichinosis.
Other Parasitic Roundworms
• Pinworms, genus Enterobius, are common parasites of
humans. They do not cause any serious disease.
• Filarial worms infect many people in tropical countries. The
most dangerous ones infect the lymphatic system and may
cause elephantiasis.
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Chapter 34
Section 2 Nematoda and Rotifera
Exploration of a Roundworm
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Chapter 34
Section 2 Nematoda and Rotifera
Phylum Rotifera
• Members of the phylum Rotifera are called rotifers.
• Most rotifers are tiny, transparent, free-living animals
that live in fresh water.
• Some can survive without water for long periods.
• Although tiny, they are truly multicellular and have
specialized organ systems.
• They use the crown of cilia around their mouth to
sweep food into the mastax.
• The digestive, reproductive, and excretory systems
empty into the cloaca.
• Some species reproduce by parthenogenesis.
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Chapter 34
Standardized Test Prep
Multiple Choice
1. What does a planarian use its pharynx for?
A. feeding
B. movement
C. reproduction
D. to respond to light
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
1. What does a planarian use its pharynx for?
A. feeding
B. movement
C. reproduction
D. to respond to light
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
2. Where do blood flukes of the genus Schistosoma
reproduce asexually?
F. in water
G. inside a snail
H. inside a cow’s intestine
J. inside a human’s blood vessels
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
2. Where do blood flukes of the genus Schistosoma
reproduce asexually?
F. in water
G. inside a snail
H. inside a cow’s intestine
J. inside a human’s blood vessels
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
3. What does a tapeworm use its scolex for?
A. to reproduce
B. to attach itself to its host
C. to eliminate excess water
D. to force food into its mouth
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
3. What does a tapeworm use its scolex for?
A. to reproduce
B. to attach itself to its host
C. to eliminate excess water
D. to force food into its mouth
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
4. Which of the following is true of most rotifers?
F. They are parasitic.
G. They live in the soil.
H. They feed with the help of cilia.
J. They have a gastrovascular cavity.
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
4. Which of the following is true of most rotifers?
F. They are parasitic.
G. They live in the soil.
H. They feed with the help of cilia.
J. They have a gastrovascular cavity.
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
The figure below shows the internal structure of a
planarian of the genus Dugesia. Use the figure to
answer the questions that follow.
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
5. What type of animal is shown in the figure?
A. flatworm
B. tapeworm
C. roundworm
D. rotifer
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
5. What type of animal is shown in the figure?
A. flatworm
B. tapeworm
C. roundworm
D. rotifer
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
6. What is the structure labeled X?
F. the brain
G. the mouth
H. an eyespot
J. a nerve cord
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
6. What is the structure labeled X?
F. the brain
G. the mouth
H. an eyespot
J. a nerve cord
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
7. What is the structure labeled Y?
A. the mouth
B. a flame cell
C. an eyespot
D. the gastrovascular cavity
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
7. What is the structure labeled Y?
A. the mouth
B. a flame cell
C. an eyespot
D. the gastrovascular cavity
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
8. fluke : schistosomiasis :: filarial worm :
F. trichinosis
G. elephantiasis
H. encysted meat
J. swimmer’s itch
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
8. fluke : schistosomiasis :: filarial worm :
F. trichinosis
G. elephantiasis
H. encysted meat
J. swimmer’s itch
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
The figure below shows the internal structure of a rotifer.
Use the figure to answer the question that follows.
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
9. Which structures are involved in excretion?
A. K and L
B. L and O
C. M and N
D. M and P
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Chapter 34
Standardized Test Prep
Multiple Choice, continued
9. Which structures are involved in excretion?
A. K and L
B. L and O
C. M and N
D. M and P
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Chapter 34
Standardized Test Prep
Short Response
Planarians and rotifers eliminate water through a
network of excretory structures that run the
length of the body.
Explain why the excretory structures in planarians
and rotifers are called flame cells.
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Chapter 34
Standardized Test Prep
Short Response, continued
Planarians and rotifers eliminate water through a
network of excretory structures that run the
length of the body.
Explain why the excretory structures in planarians
and rotifers are called flame cells.
Answer: The beating of the cilia in flame cells
draws water from surrounding tissue. It is the
motion of the cilia that resembles the flickering
of a flame.
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Chapter 34
Standardized Test Prep
Extended Response
Base your answers to parts A & B on the
information below.
Parasitic flatworms have life cycles that include
primary and intermediate hosts.
Part A Distinguish between primary and
intermediate hosts in flatworms.
Part B Sequence the life cycle of a beef tapeworm.
Identify the primary and intermediate hosts.
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Chapter 34
Standardized Test Prep
Extended Response, continued
Answer:
Part A Primary hosts nourish the adult parasite.
Intermediate hosts nourish the larval parasite.
Part B: Adult tapeworms live in the intestines of
the primary host, humans. Mature proglottids
are shed in the feces and release eggs. Eggs
ingested by cows, the intermediate host,
develop into larvae, burrow into muscle tissue,
and develop into adults when a human eats
infected, undercooked beef.
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