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Unit 4.2
Phylum Cnidaria
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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
nematocysts• Two body forms
– Polyp– Medusa
• Two germ layers• Nerve net• Still no circulatory or
respiratory systems
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Radial symmetryRadial 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
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Class Hydrozoa
• Freshwater & marine.• Cnidocytes present only on
epidermis.• Medusa (if present) with a muscular
velum that aids in propulsion.• Asexual reproduction by budding.• Sexual reproduction via gametes
produced by epidermis & released into water.
• Hydra, Ctenophores, Obelia, Man-of-War
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Class HydrozoaHydra
SpermariesSpermariesSpermariesSpermaries
OvariesOvariesOvariesOvaries
EncapsulatedEncapsulatedembryoembryo
EncapsulatedEncapsulatedembryoembryo
Sexual cycleSexual cycleSexual cycleSexual cycle Asexual cycleAsexual cycleAsexual cycleAsexual cycle
BuddingBuddingBuddingBudding
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GastrovascularGastrovascularcavitycavityGastrovascularGastrovascularcavitycavity
EpidermisEpidermisEpidermisEpidermis
MesogleaMesogleaMesogleaMesoglea
GastrodermisGastrodermisGastrodermisGastrodermis
HydraBody Wall
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Obelia• Freshwater or marine.• Live in colonies rather
than free living like hydra.
• Colonies contain two types of polyps, feeding and reproductive.
• Dual stage life cycle like other Cnidarians.
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Obelia
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Obelia
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Obelia
MedusaeGonangium Medusa bud
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Class HydrozoaGonionemus
Class HydrozoaGonionemus
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Velum
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Class HydrozoaPhysalia
Class HydrozoaPhysalia
• Commonly called the Portuguese Man-of-War.
• Not a jellyfish or even a single organism.
• Made of a colony of hydrozoans that perform specialized functions.
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Class HydrozoaPhysalia
• Gastrozooids – Feeding & digestion.
• Dactylozooids – Prey capture.
• Gonozooids – Reproduction.
• Pneumatophore – Gas-filled float.
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Class HydrozoaPhysalia
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Class Scyphozoa
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Class Scyphozoa• True Jellyfish
• Tentacles up to 70 meters in length
• Cnidocytes present in gastrodermis & epidermis
• Thick mesoglea contains amoeboid cells
• Gametes produced by gastrodermis
• All marine
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Class ScyphozoaAurelia – Moon Jellies
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Aurelia Life History
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Fig. 13.18
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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
GonadGonadGonadGonad
TentacleTentacleTentacleTentacle
PedaliumPedaliumPedaliumPedalium
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Class CubozoaThe Box Jellyfish
Class CubozoaThe Box Jellyfish
• The most venomous poison known to man.
• One brush against the skin will inject enough venom to put a full grown adult in the hospital for over a week.
• Even a full morphine drip can not relieve the pain.
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Class CubozoaThe Box Jellyfish
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Class CubozoaThe Box Jellyfish
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Class Anthozoa• Sea Anemones & Coral
• Medusa stage virtually absent
• Solitary or colonial
• Some produce protective skeletons
• Cnidocytes on tentacles and lining the gastrovascular cavity
• Mesoglea contains amoeboid cells like all other Cnidarians
• All Marine
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Class AnthozoaSea Anemone
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Class AnthozoaMetridium
Class AnthozoaMetridium
MouthMouthMouthMouth
TentaclesTentaclesTentaclesTentacles
PharynxPharynxPharynxPharynx
SeptumSeptumSeptumSeptum
Gastrovascular cavityGastrovascular cavityGastrovascular cavityGastrovascular cavity
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Symbiosis
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Class AnthozoaCorals
• 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 while gaining a home
• Mutualism
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CoralsColony of interconnected polyps
CoralsColony of interconnected polyps
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Class AnthozoaMeandrinaBrain Coral
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Class AnthozoaGorgonia
Sea Fan
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Class AnthozoaTubipora
Pipe Organ Coral
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Class AnthozoaActinodiscusMushroom Coral
Class AnthozoaAcropora
Staghorn Coral
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Coral Reefs
• 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
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Photo © McGraw-Hill Higher Education, Barry Barker, Photographer
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AnthozoaScyphozoa Cubozoa
Hydrozoa
Radial symmetry & cnidocytes
All marine
Medusa cuboid
Polyp stage reducedLoss of medusa
Cladogram of Cnidaria
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The End
