Transcript Flatworms, Roundworms, and Rotifers

Flatworms, Roundworms, and
Rotifers
Rupp
Bio II Honors
Chapter 36
Phylum Platyhelminthes
• More commonly
known as flatworms
• 3 germ layer
development
• Bilateral symmetry
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Structure and Function of
Flatworms
• Simplest organisms
with bilateral
symmetry
• Acoelomates—gases
exchanged through
skin by diffusion
• Gastrovascular
cavity—only one
opening—food in and
wastes out
• Anterior end—
sensory organs
• 18,000 species—
three classes
– Turbellaria—free-living
– Trematoda—parasitic
– Cestoda—parasitic
• Parasitic worms are
simpler than freeliving
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Class Turbellaria
• 4,500 species
• Mostly marine
• Freshwater
planarian—Dugesia
• Spade-shaped
anterior and tapered
posterior
• Wave-like motion with
mucus and cilia
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Planarian Digestion
• Scavenge dead and
decaying plant and
animal matter
• Ingest through a
pharynx
• Highly branched
gastrovascular cavity
to deliver nutrients
throughout body
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Planarian Excretion
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Planarian Nervous System
• Cerebral ganglia at
anterior—simple brain
• Ladder-like
arrangement of
nerves
• Eyespots to sense
intensity and direction
of light
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Planarian Reproduction
• Hermaphrodites
• Sexual Reproduction involves
simultaneous fertilization—each one
fertilizes the other
• Eggs are laid in protective capsules
• Asexual reproduction
– Fission or regeneration
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Class Trematoda, the Flukes
• 9,000 species of
flukes—leaf-shaped
flatworms that are
parasitic
• Some live in and
others live on
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Trematode Structure
• Cling to host with
anterior and ventral
sucker
• Anterior sucker
surrounds the mouth
and draws in host
fluids
• Nervous system is
similar to planarians,
but no eyespots
• Tegument is a
continuous sheet of
fused cells
– Made of proteins and
carbohydrates that
resist host defenses
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Trematode Reproduction
• Hermaphroditic
• Eggs are stored in a long coiled uterus
• Capable of producing tens of thousands of
eggs at a time
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Schistosoma Life Cycle
• Humans are the
primary host
• Sexual reproduction
in humans and eggs
are excreted
• Larva enter snail
intermediate host
• Development of tail
while in snail
• Cycle repeats
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Schistosomiasis
• If not all eggs leave
the human host some
can be carried to
lungs, bladder, liver,
etc.
• 200-300 million
people affected per
year
– Asia
– Africa
– S. America
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Class Cestoda
• 5,000 Species
• Commonly known as
tapeworms
• Live in the intestines
of almost vertebrates
• Humans may have
any of 7 different
species
• Source is raw or
undercooked food
• Symptoms
–
–
–
–
Digestive problems
Weight loss
Lack of energy
Anemia
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Cestode Structure
• Tegument to protect
from host defenses
• Anterior scolex—has
hooks and suckers
• Proglottids—sections
of the worm—the
older ones are
situated to the
posterior
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Cestode Structure
• Excretory and
nervous system is
similar to flatworms
• No eyespots, mouth,
gastrovascular cavity,
or digestive organs
• Nutrients are
absorbed through the
tegument
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Tapeworm Reproduction
• Hermaphroditic
• Reproductive organs in each proglottid
• As proglottids move to the posterior they
mature and produce eggs
– 100,000 eggs
– Fertilized by sperm from another proglottid—
self or other worm
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Taeniarhyncus (Beef Tapeworm)
Life Cycle
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Taenia solium (Pork Tapeworm)
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Phylum Nematoda and Rotifera
• Bilaterally
symmetrical
• Fluid-filled coelom
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Phylum Nematoda
• Commonly known as
roundworms
• Psuedocoelomates
• 1cm to 4ft in length
• Digestive tract with
mouth and anus
– Allows specialization
– Digestion
– Absorption
• Typically separate
sexes
• Cuticle—protective
outer layer
• 80,000 species
known, but potentially
500,000 species
• Free-living on land
and in fresh and salt
water
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Caenorhabditis elegans
• Research species
• Simple system
consisting of less than
1,000 cells
• 6 chromosomes
• 6,000 genes that are
human homologs
• 20,000 genes
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Genus Ascaris
• Found in pig, horse, and
human intestines
• Adult females are larger
• Males have hooked tails
to hold females during
mating
• Females can produce
200,000 eggs per day
that can be ingested
through contaminated
food and water
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Ascaris Life Cycle
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Hookworms
• Intestinal parasite
• Cutting plates that
clamp intestinal wall
• Feed on host blood
and can cause
anemia
• 400 million affected,
90% of infections in
the tropics
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Hookworm Life Cycle
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Genus Trichinella
• Humans and pigs
• Trichinosis
– Muscle pain
– Stiffness
– Death if severe
infection and many
cysts in heart
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Other Parasitic Roundworms
• Pinworm or Enterobius
– Affects 16% of adults and
30% of kids in U.S.
– No serious side effects
– Resemble small white
threads
– Live in lower intestine
– Females lays eggs around
anus at night
– Spread by scratching and
touching
• Filarial Worms
– Disease causing
roundworms
– Affects 250 million in the
tropics
– The most dangerous live in
lymph system
– Transferred via mosquitos
– Large infections cause
elephantiasis
– One species causes dog
heartworm
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Phylum Rotifera
• Psuedocoelomates
• Approx. 1,750 species
• Typically transparent freeliving organisms found in
freshwater
• Males are typically
smaller
• Can survive drought by
becoming dehydrated
and re-hydrating under
proper conditions
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Rotifer Structure
• Digestive system
– Mouth, mastax,
stomach, intestines,
cloaca, anus
• Flame cells and
excretory tubules
• Cephalization
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