Flatworms, Roundworms, and Rotifers

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Flatworms, Roundworms, and Rotifers

• Rupp
• Bio II Honors
• Chapter 36

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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
• Acoelomatesgases exchanged through skin by
  diffusion
• Gastrovascular cavityonly one openingfood in
  and wastes out

• Anterior endsensory organs
• 18,000 speciesthree classes
• Turbellariafree-living
• Trematodaparasitic
• Cestodaparasitic
• Parasitic worms are simpler than free-living

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Class Turbellaria

• 4,500 species
• Mostly marine
• Freshwater planarianDugesia
• 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 anteriorsimple 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
  fertilizationeach 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 flukesleaf-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 scolexhas hooks and suckers
• Proglottidssections of the wormthe 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 proglottidself
  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
• Cuticleprotective 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 free-living 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