Coelom:

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• Coelom
• Fluid-filled body cavity lined by cells from the
  mesoderm

• In mammals it forms the peritoneal, pleural and
  pericardial cavities

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Acoelomate
Coelomate
Pseudocoelomate
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Phylum Platyhelminthes Say What???Flat Worms
Planarians, Tapeworms, Flukes
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Characteristics of Flatworms

• Flatworms are the simplest of the worm groups
  20,000 species
• SIMPLEST ANIMALS W/ ORGANS ganglia, eye spots,
  testes, ovaries, nephridiopores
• They are found in many places and can be free
  living or parasitic.
• A flatworm can be microscopic or many feet long
  and is generally very thin.

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Characteristics of Flatworms

• Show cephalization sensory organs in front of
  head to sense food, danger, mates
• One of the best-known flatworms is the tapeworm.
  The tapeworm can get into a person's digestive
  tract and grow to enormous lengths.
• Flatworms are found in marine and fresh water.

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Body Cavity

• Acoelomate lack an internal body cavity

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Muscular-Skeletal System

• A flatworm has no skeleton. It has tiny bristles
  called cilia that help it move as well as two
  layers of muscles under its skin. It has three
  cell layers called the endoderm, the mesoderm and
  the ectoderm.

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Digestion

• Mouth/Anus It takes food in and gets rid of
  wastes through the same opening (pharynx).
• A flatworm has a gastrovascular cavity (highly
  branched) with one opening.
• It eats small worms, insects and microscopic
  matter.

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Digestion (cont.)
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Nervous System

• A flatworm has a very simple nervous system with
  two nerve cords running down either side.
• It has two simple brains called ganglia, which
  are simple bundles of nerves.
• It has two eyespots that help it sense light.

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Nervous System (cont.)
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Circulation

• NONE!!

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Respiration

• Oxygen/carbon dioxide pass through worms body by
  diffusion

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Reproduction

• Sexually hermaphrodites simultaneous
  fertilization
• Asexually A flatworm reproduces by splitting in
  two. When a flatworm is split up it immediately
  forms a new flatworm.
• Flatworm Regeneration video

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Excretion

• A flatworm gets rid of wastes through the same
  opening it takes in food. Also, have flame cells
  (w/cilia) to get rid of excess water.

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Symmetry

• A flatworm has bilateral symmetry.

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Other types of FlatwormsTapeworms
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Other types of FlatwormsFlukes
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Fluke life cycle