Transcript Chapter 34 Flatworms, Roundworms, and Rotifers Table of Contents Section 1 Platyhelminthes Section 2 Nematoda and Rotifera.

Chapter 34
Flatworms, Roundworms, and
Rotifers
Table of Contents
Section 1 Platyhelminthes
Section 2 Nematoda and Rotifera
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.
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.
Chapter 34
Section 1 Platyhelminthes
Characteristics of Flatworms
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Visual Concept
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.
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.
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.
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.
Chapter 34
Section 1 Platyhelminthes
Planarian
Chapter 34
Section 1 Platyhelminthes
Anatomy of a Planarian
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Visual Concept
Chapter 34
Section 1 Platyhelminthes
Exploration of a Flatworm
Chapter 34
Section 1 Platyhelminthes
Development of
Flatworm Embryo
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.
Chapter 34
Tegument
Section 1 Platyhelminthes
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.
Chapter 34
Life Cycle of
Schistosoma
Section 1 Platyhelminthes
Chapter 34
Section 1 Platyhelminthes
Life Cycle of Flukes
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Visual Concept
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.
Chapter 34
Section 1 Platyhelminthes
Anatomy of a Tapeworm
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Visual Concept
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.
Chapter 34
Section 1 Platyhelminthes
Life Cycle of Beef Tapeworm
Chapter 34
Section 1 Platyhelminthes
Life Cycle of Tapeworms
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Visual Concept
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.
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.
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.
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.
Chapter 34
Section 2 Nematoda and Rotifera
Exploration of a Roundworm
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.