Transcript Document 7481710

Chapter 27- Worms and
Mollusks
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I. What is a flatworm?
A. What is a flatworm?
1.
Flatworms are soft, flattened worms that
have tissues and internal organ systems.
2.
They are the simplest animals to have
three embryonic germ layers, bilateral
symmetry and cephalization.
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3. Flatworms are known as acoelomates,
meaning “without coelom.”
4. A coelom is a fluid-filled body cavity that is
lined with tissue derived from mesoderm.
5. No coelom forms between the tissues of
flatworms.
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B. Form and function in flatworms
1.
Because flatworms are thin and most of
their cells are close to the external
environment, materials can pass easily into
and out of their bodies.
2.
All flatworms rely on diffusion for some
essential body functions, such as respiration,
excretion and circulation.
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3. Other processes are carried out in
different ways in different species.
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C. Feeding
1.
Free-living flatworms can be carnivores that feed
on tiny aquatic animals, or they can be scavengers
that feed on recently dead animals.
2.
Near the mouth is a muscular tube called a
pharynx.
3.
Flatworms extend the pharynx out of the mouth.
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4. The pharynx pumps food into the
digestive cavity or the gut.
5. Parasitic worms feed on blood, tissue
fluids or pieces of cells within the host’s body.
6. Many parasitic worms obtain nutrients
from foods that have already been digested
by their host.
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D. Respiration, Circulation, and Excretion
1.
Because their bodies are so flat and thin,
many flatworms do not need a circulatory
system to transport materials.
2.
Instead flatworms rely on diffusion to
transport oxygen and nutrients to their
internal tissues.
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3. Some flatworms have flame cells
that function in excretion.
4. Flame cells are specialized cells that
remove excess water from their body.
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E. Response
1.
Most flatworms have more complex
structures for detecting and responding to
external stimuli than those of cnidarians or
sponges.
2.
In free-living flatworms, a head encloses
several ganglia, or groups of nerve cells, that
control the nervous system.
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3. These ganglia are not complex enough to
be called a brain.
4. Many free-living flatworms have what look
like eyes near the anterior end of their body.
5. Each “eye” is actually an eyespot, or
group of cells that can detect changes in the
amount of light in their environment.
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6. The nervous systems of free-living
flatworms allow them to gather information
from their environment.
7. They use this information to locate food
and to find dark hiding places beneath stones
and logs during the day.
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F. Movement
1.
Free-living flatworms typically move in two ways.
2.
Cilia on their epidermal cells help them glide
through the water.
3.
Muscle cells controlled by the nervous system
allow them to twist and turn so that they are able to
react rapidly to environmental stimuli.
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G. Reproduction
1.
Most free-living flatworms are
hermaphrodites that reproduce sexually.
2.
A hermaphrodite is an individual that has
both male and female reproductive organs.
3.
During sexual reproduction, two worms
join in a pair.
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4. The worms deliver sperm to each other.
5. The eggs are laid in clusters and hatch
within a few weeks.
6. Asexual reproduction is common in freeliving flatworms. It takes place by fission, in
which the organism splits in two.
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H. Groups of flatworms
1. Flatworms are an enormously diverse
group with many different forms.
2. Turbellarians are free-living worms. Most
of these live in fresh water, they are bottom
dwellers, live in sand or mud or under stones
and shells.
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3. Flukes are parasitic flatworms. Most flukes
infect the internal organs of their host. Look
at page 687.
4. In humans the eggs could cause clog the
blood vessels, causing swelling and tissue
decay in the lungs, liver, spleen or intestines.
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5. It affects people worldwide. Largely
found in areas in tropics or in areas that
lack proper sewage systems, where
human wastes are tossed into streams
or used as fertilizer.
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6. Members of the
class Cestoda are
called tapeworms
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7. Tapeworms are long, flat, parasitic worms
that are adapted to life inside the intestines
of their hosts.
8. There, they are surrounded by food that
has already been digested, so it can be
absorbed directly through their body walls.
They have no digestive tract.
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9. The head of an adult tapeworm, called a scolex, is
a structure that can contain suckers or hooks.
10. The tapeworm uses its scolex to attach to the
intestinal wall of its host, where it absorbs nutrients
wall of its host’s intestine.
11. Behind the scolex is a narrow region that divides
to produce many proglottids, which are segments
that make up most of the worm’s body
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12. Mature proglottids contain both male and
female reproductive organs.
13. Sperm produced by the testes or male
reproductive organs, can fertilize eggs of
other tapeworms or of the same individual.
14. If cows, fishes or other intermediate
hosts consume food or water contaminated
with tapeworm zygotes, the eggs enter the
hosts and hatch into larvae
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15. These larvae then burrow into muscle
tissue in the intermediate host.
16. If a human does not heat the meat
completely, and the human eats the meat
containing these cysts in the muscle the
larvae will grow and attach in the human’s
intestines.
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II. Round worms
A.
What is a roundworm
1.
Roundworms are slender, unsegmented
worms with tapering ends.
2.
They range in size from microscopic to a
meter in length.
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3. Most species of roundworms are freeliving, inhabitating soils; salt flats aquatic
sediments and water from Polar Regions to
the tropics.
4. Roundworms have a body cavity between
the endoderm and mesoderm tissue.
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5. It is called pseudocoelom, which
means “false coelom.”
6. The anus is the posterior opening of
the digestive track.
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B. Form and Function in Roundworms
1. Many free-living roundworms are
predators that use grasping mouthparts and
spines to catch and eat other small animals.
2. Some soil-dwelling and aquatic worms eat
algae, fungi or pieces of decaying organic
matter.
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3. They exchange gases and excrete
metabolic waste through their body
walls. They have no internal transport
system.
4. Roundworms have simple nervous
systems, consisting of several ganglia.
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5. The muscles of roundworms extend
the length of their bodies.
6. Roundworms reproduce sexually and
most species have separate sexes.
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7. An individual is either male or
female.
8. Roundworms reproduce using
internal fertilization.
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C. Roundworms and Human Disease
1.
Parasitic roundworms include trichinosiscausing worms, filarial worms, ascarid worms,
and hookworms.
2.
Trichinosis is a terrible disease caused by
the roundworm Trichinella.
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3. Adult worms live and mate in the
intestines of their hosts, which include
humans, pigs and other mammals.
4. Female worms carrying fertilized
eggs burrow into the intestinal wall and
then release larvae.
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5. Filarial worms. Which are found primarily
in tropical regions live in the blood and lymph
vessels of birds and mammals.
6. In severe infections, large numbers of
filarial worms may block the passage of fluids
within the lymph vessels.
7. This causes elephantiasis.
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8. Ascarid worms is a serious parasite of
humans and many other vertebrate animals.
9. It causes malnutrition in more than 1
billion people worldwide.
10. Species that are closely related to Ascaris
affect horses, cattle, pigs, chickens, dogs,
cats and many other animals.
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11. Today as many as ¼ of the people in
the world are infected with hookworms.
12. Hookworm eggs hatch in the soil and
wait for an unprotected foot.
13. They use their sharp tooth like plates
and hooks to burrow into the skin and enter
the bloodstream.
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14. They get in the
blood stream, are
coughed up and
swallowed where
they stay in the
intestines and suck
the host’s blood
causing weakness
and poor growth.
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D. Research on C.elegans
1. Roundworms have been making
headlines.
2. They are looking at these worms
and their genes.
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III. Annelids
A. What is an annelid?
1. Annelids are worms with segmented
bodies. They have a true coelom that is
lined with tissue derived from the
mesoderm.
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B. Form and function
1.
Annelids have complex organ systems.
Many of these systems are unique because of
the segmented body plan of this group.
2.
Annelids range from filter feeders to
predators that are fearsome.
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3. Annelids typically have a closed circulatory
system.
4. Aquatic annelids often breathe through
gills.
5. Annelids produce two kinds of waste.
Their solid waste is passed out their anus.
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6. Most annelids have a well –developed
nervous system consisting of a brain and
several spinal cords.
7. Annelids have two major groups of body
muscles that function as part of hydrostatic
skeleton.
8. Most annelids reproduce sexually.
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9. Some species use external fertilization and
have separate sexes.
10. Other annelids (like earthworms and
leeches) are hermaphrodites.
11. Each worm produces sperm and eggs.
Individuals rarely fertilize their own eggs.
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12. When eggs are ready for
fertilization, a clitellum secretes a
mucus ring into which eggs and sperm
are released.
13. Fertilization takes place within this
ring.
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C. Groups of annelids
1.
Oligochaetes are annelids that typically
have streamlined bodies and relatively few
setae compared to polychaetes.
2.
Most oligochaetes live in soil or fresh
water.
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3. All earthworms leave castings as
their solid waste.
4. Some species of earthworms can
leave castings up to 18 cm long and 2
cm wide!
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5. The class Hirudinea contains the leeches,
most live in moist habitats.
6. Leeches are typically external parasites
that suck blood and body fluids of their host.
7. Leeches were once commonly used to
treat medical conditions.
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8. Today doctors still uses leaches to
reduce swelling after surgery!
9. Leeches can suck blood 5 times
their own weight!
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14. The ring slips off the worm’s body
and forms a protective cocoon.
15. Young hatch a few weeks later.
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10. The class Polychaeta contains
sandworms, bloodworms and their
relatives.
11. Polychaetes are marine annelids
that have paired, paddle like
appendages tipped with setae.
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Sand worm
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D. Ecology of Annelids
1.
Earthworms and many other annelids
spend their lives burrowing through soil,
aerating it, and mixing it to depths of 2
meters or more.
2.
Their tunnels provide passageways for
plant roots and water and allow the growth of
beneficial oxygen requiring soil bacteria.
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3. Earthworms are also very important
in the food chain- birds.
4. In the sea, annelids participate in a
wide range of food chains.
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IV. Mollusks
A. What is a mollusk?
1. Mollusks are soft-bodied animals
that usually have an internal or external
shell.
2. Mollusks include snails, slugs, clams,
squids, and octopi.
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3. These animals are all placed in same
phylum because they share similar
developmental stages.
4. Many aquatic mollusks have freeswimming larval stage called
trochophore.
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B. Form and function in Mollusks
1. Mollusks have true coelom
surrounded by mesoderm tissue.
2. The body plan of most mollusks has
four parts: foot, mantle, shell and
visceral mass.
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3. The muscular foot takes many forms,
including flat structures for crawling.
4. The mantel is a thin layer of tissue that
covers most of the mollusks body.
5. Glands in the mantle that secrete calcium
carbonate make the shell.
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6. Just beneath the mantle is the visceral
mass, which consists of the internal organs.
7. Mollusks can be herbivores, carnivores,
filter feeders, detritivores, or parasites.
8. Herbivorous mollusks use their radula to
scrape algae off rocks or to eat the soft
tissues of plants.
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9. Octopi and
certain sea slugs use
their sharp jaws to
eat their prey.
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10. Clams, oysters
and scallops lead a
quieter existence by
filter feeding using
feathery gills.
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11. Aquatic
mollusks such as
snail, clams and
octopi typically
breathe using gills
inside their mantle
cavity
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12. The circulatory system of mollusks is
open.
13. Open circulatory system blood is pumped
through vessels by a simple heart.
14. Open circulatory system is good for slow
animals like snails and clams
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15. Fast animals like octopi and squid have a
closed circulatory system.
16. Cells of the body release nitrogencontaining waste into the blood in the form of
ammonia.
17. The response of mollusks varies from
mollusks to mollusks.
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18. Clams and other two-shelled
mollusks typically lead inactive lives.
19. Octopi and their relatives are active
and intelligent predators that have the
most developed nervous system.
20. They have well developed brains.
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21. Octopi are capable of complex
behavior such as opening a jar to get
food inside.
22. They can be trained to get rewards
or avoid punishment.
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23. Mollusks move in many different
ways. Snails secrete mucus along their
foot.
24. Octopus move by jet propulsion.
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25. Mollusks reproduce in a variety of
ways.
26. Many snails and two shelled
mollusks reproduce sexually by external
fertilization.
27. Some mollusks are hermaphrodites
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C. Gastropods –stomach foot animals.
2. Gastropods are shell-less or single
shelled mollusks that move by using a
muscular foot.
3.
Snails, slugs are gastropods.
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4. Bivalves – “two shelled animals”
held together by powerful muscles.
5. Clams, mussels, oysters and scallops
are bivalves
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6. Cephalopods –head foot animals
7. Cephalopods are typically soft bodied
mollusks in which the head is attached to a
single foot.
8. The foot is divided into tentacles or arms.
9. Octopus, squid and nautiluses are
cephalopods
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D. Ecology of mollusks
1.
Mollusk play differ rent roles in living
systems.
2.
They are important in the food chain.
3.
Also they clean the environment.
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The End
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