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ANIMAL KINGDOM
PHYLUM CNIDARIA
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ABBOTTSCOLLEGE
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PHYLUM CNIDARIA
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Includes between 9
000 and 11 000
species
Includes the plant
like hydroids, the
flower like sea
anemones, the jellyfish, bluebottles and
the hard corals
BODY PLAN OF CNIDARIA
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Acoelomate (have no body cavity)
Radial symmetry
Diploblastic tissue layers
Digestive cavity with a single opening
The body wall is made up of three layers
But there are only two layers of cells
(the ectoderm and endoderm)
The middle layer (mesogloea) is jelly
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DIPLOBLASTIC TISSUE LAYERS
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The ectoderm forms
the epidermis
The endoderm forms
the gastrodermis (around
the gut)
There is a layer of jelly
between the two = mesogloea
BODY WALL CNIDARIA
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RADIAL SYMMETRY
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Suits their sessile or free floating mode of
living
Makes them aware of what is happening all
around them
DIGESTIVE CAVITY WITH A SINGLE OPENING
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Serves as both a mouth and an
anus
Inefficient digestive system
Have a ring of tentacles around
the opening to catch food
Have specialised stinging cells
or cnidocytes
Which contain stinging
organelles called nematocysts
to capture their prey and
defend themselves against
predators
Hydra is a genus of small, simple, fresh-water animals that possess radial
symmetry.
Hydra are predatory animals belonging to the phylum Cnidaria
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REPRODUCTION
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Have a dimorphic life cycle (develop two basic
body forms)
Medusa
Free swimming and umbrella shaped
 Develops gonads
 Reproduces sexually to produce a free-swimming
planula larva
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Polyp
Develops from the larva
 May occur singly (eg anemones)
 Or in enormous marine colonies (eg corals)
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Life cycle Cnidaria
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Coral
Coral Reef
Corals are marine invertebrates
in phylum Cnidaria typically
living in compact colonies of
many identical individual
"polyps".
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TO DO
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PASTE IN DIAGRAMS
IN YOUR WORKBOOK
TEXTBOOK PAGE 78
LEARNING ACTIVITY 1
QUESTIONS 1, 2 AND 3
BODY PLANS OF ANIMALS
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THE END