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Cnidarians Jellyfish, corals, hydra and anemone Defining Characteristics Radial Symmetry Tentacles with nematocysts (stinging cells) No cephalization (no head) Two stages: polyp and medusa Endoderm and ectoderm Radial Symmetry

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Jellyfish, corals, hydra and anemone

defining characteristics
Defining Characteristics
  • Radial Symmetry
  • Tentacles with nematocysts (stinging cells)
  • No cephalization (no head)
  • Two stages: polyp and medusa
  • Endoderm and ectoderm
radial symmetry
Radial Symmetry

Like a radial tire, can be dissected along any plane into equal mirror images.

nematocysts stinging cells
Nematocysts – stinging cells
  • Stinging barb at the end of tentacles
  • The barb is discharged like a toy popgun. Some contain toxins.
nervous system
Nervous System
  • No cephalization (no head)
  • No central Brain
  • Impulses cause muscle contractions and responses
stages in cnidarian life cycle
Stages in Cnidarian Life Cycle
  • Polyp: sessile and tube-shaped with the opening (mouth) facing up and surrounded by tentacles
  • Medusa: free-swimming form with mouth and tentacles facing down
reproduction in cnidarians
Sexual: only in medusa stage

Asexual: in either stage thru budding

A budding hydra

Reproduction in Cnidarians
body design
Body Design
  • Tentacles capture food and carry to the mouth.
  • Waste is expelled through the mouth.
types of cnidarians
Types of Cnidarians
  • Hydrozoans: the hydras
  • Scyphozoans: the jellyfish
  • Anthozoans: corals and sea anemone
  • Include the hydra and the man-of-war
  • Mostly sessile
man of war

Made of a colony of polyps, each specialized for a single task. One polyp forms the gas-filled float, while others are responsible for feeding or reproduction.

scyphozoans the jellyfish
Scyphozoans: The Jellyfish
  • Can be luminescent (create their own light)
  • The medusa stage is dominant
  • The sting is venomous
  • Warm Water only
  • Forms colonies
  • Reefs formed from new coral build on old layers.
  • Reefs provide ecosystem for marine animals.
  • Reefs grow at 2mm/year.
zooxanthellae and coral
Coral have a symbiotic relationship with zooxanthellae, a photosynthetic protista.

The bright coral colors come from zooxanthallae

The greenish color of this color is due to the zooxanthellae which live inside of it.

Zooxanthellae and Coral
sea anemone
Sea anemone
  • Unlike coral, each anemone lives as an individual
  • Anemone can live for centuries
commensalism anemone and clownfish
Commensalism: anemone and Clownfish

Clownfish are immune to the anemone toxins, and can live safely within the tentacles, protected from predators. The anemone isn’t helped or hurt by the clownfish.