Transcript Phylum: Cnidarians

Phylum: Cnidarians
What is a Cnidarian?
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A cnidarian is an
invertebrate
It uses stinging cells
to capture prey
Examples:
– Jellyfish
– Corals
– Sea Anemones
Body Structure
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All cnidarians have the following
characteristics:
– Radial symmetry
– A hollow central cavity
– Tentacles with stinging cells
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However, cnidarians can have one of 2
different body plans.
– Polyp
– Medusa
Body Plans
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Polyp
– Mouth opens at top
– Vase-shaped
– Attached to a surface
– Examples: Hydra, Sea
anemone, Coral
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Medusa
– Mouth opens down
– Tentacles point down
– Adapted for a swimming
life
– Examples: Jellyfish
Activity: Color Code a Cnidarian
Endoderm
Tentacle
Jelly-like layer
(Mesoglea)
Ectoderm
Tentacle
Obtaining Food
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Stinging cells inject venom which paralyzes
the prey
– THINK! – Why are clown fish resistant to the
toxins given off by sea anemones?
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Tentacles pull the prey into the mouth
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Digestion happens in the body cavity
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Waste is expelled back out through the
mouth
Movement
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Cnidarian movements are directed by nerve cells that
spread throughout the cnidarians body like a basketball
net
Jellyfish swim through water
Hydras can be found in freshwater and turn somersaults
or use their tentacles to move
– Watch these Hydra Movies
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http://micro.magnet.fsu.edu/optics/olympusmicd/galler
ies/moviegallery/pondscum/coelenterata/hydra/index.h
tml
Sea anemones stretch out, shrink down, and bend
slowly from side to side
Reproduction
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Asexual
– Budding is most common in hydras,
corals, sea anemones where these polyps
just pull apart forming two new polyps.
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Sexual
– Can occur during the life cycle of certain
cnidarians such as the jellyfish
Life Cycle of A Jelly Fish
Life on a Coral Reef
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Coral polyps produce a hard, stony skeleton
around its soft body once attached to a hard
surface.
Coral polyps then continue to reproduce
asexually
Over time, reefs build up from the sea floor
and make great homes for other sea life
Video Quiz
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Watch the following clip:
– Coral Ecosystems (5:59)
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There will be a short video quiz
following the clip.
Make sure to take good notes! You
can use your notes for the video quiz!