Flatworms Phylum: PLATYHELMINTHES

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FlatwormsPhylum PLATYHELMINTHES
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VS.
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Class Turbellariaincludes Planarians
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Class CestodaIncludes Tapeworms
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Class TrematodaIncludes Flukes
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II. Body Plan/Structure

• Flatworms demonstrate a bilaterally symmetrical
  body plan
• They are dorsoventrally flattened and lack a
  skeleton

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II. Body Plan/Structure cont

• They have a highly branched gastrovascular cavity
  .
• There is only one opening which serves the
  function of both the mouth and anus (not
  excretion)

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• They have three germ layers
• Ectoderm Outside
• Endoderm Inside
• Mesoderm Middle layer of tissue between the
  ectoderm and the endoderm
• Though Flatworms have three germ layers they are
  acoelomates and have no body cavity

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• Flatworms do have true organs and primitive organ
  systems that are used for digestion and excretion

• Flatworms are also the most primitive organisms
  to show cephalization.
• The head region of Flatworms contains a
  concentration of nerve tissue called ganglia
  (singularganglion) that resembles a primitive
  brain.

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Cephalization
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• They have two nerve cords that run from the
  ganglia in the head region along the ventral side
  of the worm to the tale region
• In the head region of Flatworms are two eye-spots
• They also have lobes on the side of their head
  called auricles

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Auricles
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Feeding

• Flatworms have a mouth/anus which is connected to
  the gastrovascular system through a long muscular
  pharynx.
• Small invertebrates or the remains of dead
  animals are taken into the mouth/anus by the
  muscular pharynx

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• The food is then digested in the highly branched
  gastrovascular cavity
• The nutrients moves from the gut into the body
  cells by diffusion

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Respiration

• Respiration occurs by diffusion

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Internal Transport

• Nutrients and oxygen in the gut are simply
  absorbed into the body cells by the process of
  diffusion

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Excretion

• Most undigested food is released directly out of
  the anus/mouth Pharynx
• A flame cell is a specialized excretory cell
• Flame cells function like a kidney, removing
  waste materials.
• The beating of cilia resembles a flame, giving
  the cell its name.

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Nerve Response

• Flatworms are able to sense and respond to at
  least three forms of stimuli
• Sense and respond to light The eye-spots can
  detect light and allow the Flatworms to respond
  to it
• Sense and respond to chemicals Pits on the side
  of their head regions can sense chemicals in the
  water and allow the Flatworms to respond (like
  smelling)
• Sense and respond to touch The auricles on
  either side of the head region can sense touch
  and allow the Flatworms to respond

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• The ganglia in the head region relay messages
  from the sensory organs down the nerve cords to
  the rest of the body. The nerve cords can
  control muscles in the body which allow the
  Flatworms to move or eat.

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Auricles
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Movement

• The flatworms move across a surface using cilia
  on their ventral surface
• They can also move by contracting circular and
  longitudinal muscles that lay just below the
  ectoderm. These muscles are controlled by the
  nerve cords.

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Reproduction

• Asexual Reproduction
• Flatworms can asexually reproduce through a
  process called fission. The anterior and
  posterior ends hold a surface and the midsection
  constricts. This results in two new flatworms,
  one from the anterior end of the original
  flatworm and the other from the posterior end of
  the original flatworm.

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Reproduction

• Flatworms can also regenerate parts they have
  lost.

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• Sexual Reproduction
• Flatworms are hermaphroditic
• After two flatworms have copulated they release
  sacs of fertilized eggs and attach them to a
  surface

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Parasitic Flatworms Tapeworms

• The tapeworm has an anterior end called a scolex
  with complicated hooks for attaching to the
  intestines of its host.
• The tapeworm does not have a mouth or digestive
  system. Instead they bath in the pre-digested
  fluids of their host and absorb nutrients
  directly into their body cells

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Hooks
Scolex
Suckers
Proglottids
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Lifecycle of a Tapeworm
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Phylum Platyhelminthes The flat worms
www.onacd.ca
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4 Classes of Phylum Platyhelminthes
TREMATODA flukes
CESTODA tapeworms
MONOGENEA small, parasitic flatworms
TURBELLARIA - small, free-living flatworms
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Identifying Characteristics of the Phylum
Platyhelminthes

• Acoelomate
• Exhibit bilateral symmetry
• Have a bilateral nervous system with
  cephalization at the head end. Some species
  exhibit eyespots sensitive to light
• Possess a Gastrovascular Cavity (GVC) and
  primitive organ systems for digestion and
  excretion
• Do not have a circulatory or respiratory system
  but do take in O2 through their body surface
  (integumentary exchange)
• Hermaphroditic can reproduce sexually (do not
  self fertilize) or asexually by regeneration
• Are motile and utilize an undulation form of
  motion
• Found in marine, freshwater and damp terrestrial
  habitats

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Free-living FlatwormsPlanaria Dugesia tigrina

• Freshwater, free-living flatworm
• Moves by beating cilia and gliding on a film of
  mucus
• 3-12mm in size
• Have a single opening to their stomachs in the
  middle of their bodies
• Possesses two eyespots (ocelli) that are
  sensitive to light
• Carnivorous (eat daphnia and midges)
• Common to most parts of the world
• Reproduce by asexual reproduction and capable of
  regeneration (see next slide)

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Planaria Regeneration

• Planarians will spontaneously detach the tail end
  of their bodies and each half will regenerate
  into a full size flatworm
• Planarians can be cut either transversally (shown
  above) or dorsally and most will regenerate into
  a full size worm
• Super Cool Fact the smallest piece of planarian
  to ever regenerate in a lab into a new planarian
  was 1/279th of a planarian! Thats approximately
  10,000 cells!

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Parasitic FlatwormsThe pork tapeworm Taenia
solium

• Infects pigs and humans
• Lives in the intestine of its host and passes
  eggs through the feces
• Highly adapted to constant internal environments
• Lacks sensory organs, coordination for mobility
  and a digestive system (more room for
  reproductive structures!)
• Have a modified epidermis tegument which
  protects against the digestive enzymes and the
  immune systems of the host
• Can reach 7m in length in humans!
• Are flat and long which maximizes absorption of
  nutrients from the host

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The tapeworm up close and personal.

• The head end has a scolex with four suckers (two
  seen here) that help it attach to the intestine
  of its host
• The body is separated into sections called
  proglottids that house highly developed
  reproductive systems (darkened areas) capable of
  producing hundreds of thousands of eggs and sperm

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Life cycle of the Pork Tapeworm
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Super cool Flatworm Fact

• the largest tapeworm ever reported was in a sperm
  whale and was 30 meters in length!

Tapeworm Scolex