Ch. 36 Platyhelminthes

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Ch. 36 Platyhelminthes

• Phylum platyhelminthes
• Flatworms
•   3 cell (germ) layers
• More complex than sponges, cnidarians and
  ctenophores
• Bilateral symmetry (left and right side)

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3 Classes

• class turbellaria
• planaria (free living)
• class trematoda
• flukes (parasitic)
• class cestoda
• tapeworms (parasitic)
• These three classes make up 18,000 species

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Structure and Function

• Simplest animal with bilateral symmetry
•  Develops from 3 germ layers
• 1.   ectoderm (outer layer)
• 2.   mesoderm (middle layer)
• 3.   endoderm (inner layer)
•  In flatworm, all 3 germ layers are pressed
  against each other to form solid body
• Belong to group called acoelomate which means
  without body cavity

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A. Respiration

• Since flat shape, all cells are in relative
  contact to its environment, so each cell
  exchanges gases by diffusion. It has no
  circulatory or respiratory system.

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B. Digestion

•   Gastrovascular cavity is a gut with single
  opening.
• Food taken in, digested, and all waste back out
  same opening.

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C. Nerves

• Located in anterior end, called cephalization.

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1. Turbellaria non parasitic

•   Majority live in ocean
•   Some in fresh water
• Planaria dugesia (known as Planaria)
• Move in water using wave like motion
• Move on ground by producing mucous and using
  cilia to glide on it

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Planaria
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Planarian Anatomy
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A. Digestion

• Feed on decayed plant or animal
•  Food ingested through pharynx (muscular tube)
  extended through middle of body
•  Goes to gastrovascular cavity
•  Cells here absorb nutrients
• draw p.710 36-2 a

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Digestion
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B. Excretion

• To get rid of waste
•  Through network of excretory tubules
•  Run length of body
•  Connects to flame cell which are enclosed
  tufts of beating cilia
• Draw p.710 36-2 b

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C. Nerves

•   2 clusters of nerve cells at anterior end
  called cerebral ganglia which serves as simple
  brain
• Ganglia receive information from sensory
  cells
•   Transmit signals to muscles along nerves
•   Has ability to learn moves from light
•  Uses eyespot near ganglia to sense
  environment
• Draw p.710 36-2 c

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D. Reproduction

•  Hermaphrodites
• When reproduce sexually, they simultaneously
  fertilize each other
•  Usually asexual in summer by regeneration
• They attach posterior end to something, anterior
  end moves until it splits. This is fission. Each
  half then regenerates into 2 complete planaria.
• Draw p.710 36-2 d

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2. Class Trematoda

• Flukes
• Leaf shape parasites
• Difference between free-living and parasitic
  is that parasitic flatworms have simpler
  structures
• Live inside host or outside on host

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A. Digestion

• Attaches itself with anterior and ventral
  sucker (see fig. 36-3 p.711)
•  Anterior sucker is around mouth
• Draws hosts body fluid into gastrovascular
  cavity
• Wastes go out the same opening

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B. Nerves

• No eyespots
• Entire external surface is covered by a sheet of
  fused cells called tegument which protects fluke
  against host

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C. Reproduction

•   Hermaphrodites but sexual reproduction
  occurs
•   Human is the primary host (this is where
  harm can be done)
•   Adult worm lives in human blood vessels
•   Eggs and sperm fertilize
• Some fertilized eggs make it to hosts
  bladder and intestines and get excreted in urine
  or feces

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Reproduction

• These eggs make it to fresh water and
  develop into ciliated larvae
• These larvae find a particular species of
  snail. They burrow into snails tissue and
  asexual reproduction takes place. Snail is
  intermediate host (no harm is done here)
• Larvae develop tails and leave
• Enter skin of human and begin cycle again
• Bad in Asia, Africa and S. America
• Draw life cycle transp. 149 also on p.712 fig.
  36-4

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3. Class Cestoda

• Tapeworms
• Parasitic
• In intestines of most vertebrates
• Up to 7 species can affect humans
• Get through raw or undercooked food, which
  contains eggs or larvae
• Causes digestive problems, weight loss, lack of
  energy and anemia

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Tapeworms
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A. Digestion

• No mouth
• No gastrovascular cavity
• No digestive organs
• Absorb nutrients directly from hosts digestive
  tract through its own tegument

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B. Structure

• Anterior is knob-shaped called scolex which
  has hooks and suckers
• Short neck connects to proglottids (draw
  structure fig. 36-5 p. 713)
• As tapeworm grows, it adds new proglottids
  behind scolex, and pushes others behind
•  Can be 30-35 ft. in length

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C. Excretory

• Out same manner as absorption

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D. Nerves

•  No eyespots
•  No light sensitive structures
• Have tegument which is close to environment

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E. Reproduction

• Sperm from 1 proglottid fertilizes eggs from
  itself or another worm
• Has 2 hosts
• primary host is human
• intermediate host is cow or pig
• Draw life cycle of tape worm transp. 150 or fig.
  36-6 p. 714

• Hermaphrodites
• Each proglottid contains both sex organs
• Eggs stored in uterus
• Oldest proglottids have most eggs (up to 100,000)