1 Unit 4.2 Phylum Cnidaria. 2 Phylum Cnidaria Radial symmetry Mouth at oral end surrounded by tentacles. One opening into and out of gastrovascular cavity.

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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