Phylum Cnidaria

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Phylum Cnidaria
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Basic Info.

• Marine invertebrates nearly 9000 species
• Made up of jellyfish, corals, sea anemones, and
  hydras.
• Found everywhere in water
• Prefer warmer climates.

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• First group to have both specialized tissues and
  symmetry
• Are called true animals or eumetazoans
• Early in their development, the embryos of most
  eumetazoans develop three distinct cell layers

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• Forming new layers is called GASTRULATION
• Takes place in developing embryos.
• The layers include the ectoderm, mesoderm
  endoderm

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Body Structure

• A diverse group, but all posses same basic
  structure
• Radial symmetry all parts arranged around a
  central axis like the petals in a daisy.

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Radial Symmetry
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• All are carnivores that capture their prey by
  tentacles that surround their mouth
• These tentacles bear stinging cells called
  cnidocytes
• Within each cnidocyte is a small harpoon called a
  nematocyst, used to spear their prey

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Nematocyst
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• Simple nervous system
• Have cells that contract like muscles

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Gastrovascular Cavity

• Is the mouth of the animal.
• Digestion is extracellular in the digestive
  cavity

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Reproduction

• Cnidarians reproduce asexually and sexually.
• Asexual reproduction by budding

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• Cnidarians display two different body forms
• gtPolyp-tube shaped stage, that has a mouth
  surrounded by tentacles

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Polyp
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• gtMedusa-stage that has a body form like an
  umbrella with tentacles

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Class Scyphozoans

• Jellyfish
• Main body form is medusa
• Most medusa can swim move freely.

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Medusa body form
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Class Hydrozoans

• Most species have both polyp and medusa stages
• Common example Hydra
• Exists only as a solitary polyp, basal disk
• Budding can take place

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• Hydra are common in freshwater (polyp body form)

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Class Anthozoa

• Corals, Sea fans and Sea anemones
• Builders of the most complex ecosystems on the
  planet.
• Are dependant on Symbionts
• Loss of symbionts is deadly
• Most can only exist in shallow water.

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Corals
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Sea Anemones

• Largest and most complex of the Cnidarians
• unlike coral, sea anemonnes live as individual
  animals
• can be found in tropical, temperate, and arctic
  seas

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Sea Anemone