Phylum Cnidaria
BIO 2215
Oklahoma City Community College
Dennis Anderson
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Phylum Cnidaria
• Radial symmetry
• Mouth at oral end
surrounded by tentacles.
• One opening into and out
of gastrovascular cavity.
• Cnidocytes that discharge
pneumatocysts
• Two body forms
– Polyp
– Medusa
• Two germ layers
• Nerve net
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Radial symmetry
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Mouth and Tentacles
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Fig. 13.2
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Generalized Cnidarian Life Cycle
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Cnidocyte Structure and Nematocyst Discharge
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Diploblastic - 2 germ layers
– Epidermis - outer covering (ectoderm)
– Mesoglea - middle non-living jelly-like layer
– Gastrodermis - lines gastrovascular cavity
(endoderm)
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Cnidarian Body Wall
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Nervous System
• Nerve cells, arranged in a nerve net.
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Class Hydrozoa
• Freshwater & marine.
• Cnidocytes present only on epidermis.
• Medusa (if present) with a muscular
velum.
• Mesoglea without ameboid cells.
• Asexual reproduction by budding.
• Sexual reproduction via gametes
produced by epidermis & released into
water.
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Class Hydrozoa
•
•
•
•
Hydra
Obelia
Gonionemus
Physalia
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Class Hydrozoa
Hydra
Encapsulated
embryo
Ovaries
Budding
Spermaries
Sexual cycle
Asexual cycle
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Hydra
Body Wall
Gastrovascular
cavity
Gastrodermis
Mesoglea
Epidermis
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Fig. 13.9
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Obelia
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Obelia
Gonangium
Medusa bud
Medusae
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Class Hydrozoa
Gonionemus
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Class Hydrozoa
Gonionemus
Velum
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Class Hydrozoa
Physalia
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Class Scyphozoa
• Tentacles up to 70
meters in length
• Cnidocytes present in
gastrodermis & epidermis
• Thick mesoglea contains
ameboid cells
• Gametes produced by
gastrodermis
• All marine
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Class Scyphozoa
Aurelia
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Aurelia Life History
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Fig. 13.18
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Planula Larva
Ciliated larva then
can swim to a new
location
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Aurelia
Mesoglea
Eggs
Gastrovascular
cavity
Mouth
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Aurelia
Oral arm
Gastric pouch
Mouth
Tentacles
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Class Cubozoa
• Medusa dominant &
cuboid
• Tentacles arise at four
corners from blade-like
pendalium.
• All marine
• Strong swimmers which
prey primarily on fish
• Stings of some may be
fatal within minutes to
humans.
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Class Cubozoa
Gonad
Pedalium
Tentacle
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Class Cubozoa
Chironex Sea Wasp
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Class Anthozoa
• Medusa stage absent
• Solitary or colonial
• Some produce protective
skeletons
• Gastrovascular cavity
subdivided by at least 8
mesenteries
• Cnidocytes on mesenteries
• Mesoglea contains ameboid
cells
• All Marine
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Class Anthozoa
Sea Anemone
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Class Anthrozoa
Metridium
Tentacles
Mouth
Pharynx
Septum
Gastrovascular cavity
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Symbiosis
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Class Anthozoa
Corals
• Protective skeleton of
calcium carbonate
• Polyp retracts when
not feeding
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Zooxanthellae
• Photosynthetic
dinoflagellates
(brown)
• Live in corals
• Provide nutrients for
coral by
photosynthesis
• Mutualism
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Corals
Colony of interconnected polyps
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Class Anothozoa
Meandrina
Brain Coral
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Class Anothozoa
Gorgonia
Sea Fan
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Class Anothozoa
Tubipora
Pipe Organ Coral
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Class Anothozoa
Actinodiscus
Mushroom Coral
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Class Anothozoa
Acropora
Staghorn Coral
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Coral Reefs
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Formed over thousands of
years from successive layers of
coral skeleton deposits
(calcium carbonate forms
underwater mountains of coral
animal skeletons)
The underwater equivalent of
the amazon jungle- very high
species diversity and biomass
Reefs contain sponges, colonial
hydrozoans, anemones, many
varieties of coral, fish, many
types of worms we’ve not
discussed, not to mention
bryozoans, ctenophores,
protists, bacteria, etc etc..
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Coral Reef Ecosystem
Photo © McGraw-Hill Higher Education, Barry Barker, Photographer
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Cladogram of Cnidaria
Anthozoa
Scyphozoa
Hydrozoa
Cubozoa
Medusa cuboidal
Loss of medusa
Polyp stage reduced
Septa divide
gastrovascular cavity
Radial symmetry,
cnidocytes, planula larva
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The End
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