Phylum Platyhelminthes

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Phylum Platyhelminthes

• Tapeworms, Flukes, and Flatworms

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Tissue Layers

• There are three tissue layers present in the
  embryo. (Triploblastic)
• Outer germ layer-the ectoderm
• Inner germ layer-the endoderm
• Middle germ layer-the mesoderm
• They have a solid body with only one opening to
  the outside. Acoelomates (without a coelom)

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Appearance of the Animal

•   (invertebrate zoology) A phylum of
  invertebrates composed of bilaterally
  symmetrical, nonsegmented, dorsoventrally
  flattened worms characterized by lack of
• coelom, anus, circulatory and respiratory
  systems, and skeleton.

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Development of the Body System

• The body is that of an elongated organism that is
  dorsally ventrally flattened with bilateral
  symmetry. Distinct tissues and organ systems are
  found, but the organs are not located in a body
  cavity. Cross sections of these animals show that
  there is no body cavity and the digestive tract
  is found in the mesenchyme.
• There is only one opening, so it is described as
  a sac-like system. Food enters the mouth and is
  digested in a branched gastro vascular cavity.
  Any non-digestible residue must be regurgitated
  back through the mouth.

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Development of the Body System

• Muscle layers are well developed and controlled
  by a distinct nervous system with two
  longitudinal nerve cords that run the length of
  the body.
• There is no separate skeletal system and body
  support is by hydrostatic pressure or by a
  cuticle.
• There are no special organs for respiration and
  circulation. Diffusion across the body surface or
  from the gastro vascular cavity to the body cells
  fulfills these functional needs.
• Individuals may have both male and female sex
  organs, producing sperm and eggs. Fertilization
  is internal.  Microscopic fertilized eggs are
  released. Development may be direct into
  miniature adult forms or indirect through a
  independent larval stage.

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Body System Advantage

• It has flame cells which are an evolutionary
  advantage over Cnidarians.
• The flatworm has two simple brains
• They are able to self fertilize

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Tapeworm
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Life Cycle of a Tapeworm
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Parasitic

• In humans, tapeworms cause abdominal distention,
  flatulence, intermittent abdominal cramping, and
  diarrhea with onset about 10 days after
  consumption of raw or insufficiently cooked fish.
  
• Flukes can causes an illness in dogs that may be
  serious or even fatal, and they also can cause
  illness in humans.  

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Fluke
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Life Cycle of a Fluke
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Life Style

• Members of one class (the turbellaria) are
  free-living, while the other two classes
  (trematoda and cestoda) are obligate parasites
• Turbellaria help feed aquatic animals and
  trematoda and cestoda make people and animals
  sick.

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• The structure of a Turbellaria