Bilateria

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Bilateria

• Scott Harris

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Introduction

• Group made up of many phyla including
  invertebrates and vertebrates.
• These animals are bilaterally symmetrical.
• Have at least two cell layers.
• Contain organ systems including a primitive brain.

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Platyhelminthes

• The most primitive of all the phyla.
• Mesoderm is called parenchyma.
• Has no anus.
• Nerve system connected to brain.
• Primitive kidneys.
• Include flatworms, flukes and tapeworms.

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Nemertea

• Include marine, freshwater and terrestrial
  species.
• More evolved than Platyhelminthes.
• Circulatory system.
• Gut and anus.
• Proboscis.
• Longest animal in the world.

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Rotifera

• Freshwater species.
• Do not have respiratory or circulatory systems.
• Attach to substrate via adhesive secretions from
  the toes.
• Undergo eutely, so as they grow the number of
  cells does not increase, only their size.
• Some classes are only female.

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Sipuncula

• Marine species.
• Range from mms to 1m.
• Made up of a trunk, introvert, mouth and
  tentacles.
• Tentacles trap food and passed into the mouth.
• Has a U-shaped digestive tract.

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Nematoda

• Parasitic.
• No internal segmentation.
• No circular muscles.
• Renette cells replace the kidneys, circulatory
  system and respiratory system.
• Undergo eutely.