phylum cnidaria. phylum cnidaria jellyfish, hydras, sea anemones, corals carnivorous radial symmetry...
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Phylum
Cnidaria
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Phylum Cnidaria
• jellyfish, hydras, sea anemones, corals
• carnivorous• radial symmetry• have stinging cells called
cnidocytes which contain nematocysts
• nematocysts are poison filled harpoons used for catching prey
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Radial Symmetry Bilateral Symmetry
Planes ofsymmetry
Plane ofsymmetry
Ventral side
Dorsal side
Posterior end
Anterior end
Body Symmetry
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Cnidarian Body Plan
• radial symmetry with tentacles• two stages to life cycle
– Polyp– Medusa
• body surrounds an internal space, gastrovascular cavity
• gastrovascular cavity lined with gastroderm (tissue layer)
• epidermis is outermost layer• mesoglea between gastroderm and epidermis
(jelly-like)
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Polyp
• Sessile
• cylindrical body
• mouth faces upwards
• tentacles point up
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Medusa
• Motile
• bell-shaped body
• mouth underneath
• tentacles point down
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Epidermis
Mesoglea
Gastroderm
Mesoglea
Gastrovascular cavity
Mouth/anus
Tentacles
Tentacles
Mouth/anus
Gastrovascularcavity
Polyp
Medusa
The Polyp and Medusa Stages
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Feeding
• prey is paralyzed and pulled into the gastrovascular cavity
• digestion is extracellular
• nutrients are absorbed by gastroderm
• nutrients dispersed by diffusion
• anything not digested leaves through the mouth/anus
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Respiration, Circulation, Excretion
• all are done by diffusion through the body wall
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Response
• specialized cells of the nerve net receive stimuli
• nerve net is evenly distributed throughout the body
• no true brain
• also have cells to determine light intensity and gravity
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Movement
• done by hydrostatic skeleton in polyps
• done by jet propulsion in medusa (like a water pump)
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Reproduction: Sexual
• fertilization is external
• separate male and female organisms
• zygote forms a free-swimming larva
• larva grows into a new polyp
• polyp then buds to form new medusa
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Reproduction: Asexual
• polyps reproduce by budding
• new polyps may grow off the side of existing polyps
• polyp may produce medusas
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Fertilization occurs in the open water, producing many diploid zygotes.
Sperm (N)
Egg (N)
Haploid
Diploid
FERTILIZATION
MEIOSIS
Male medusa(2N)
Zygote (2N)
Polyp
Buddingpolyp
Youngmedusa
Female medusa(2N)
Each zygote grows into a ciliated larva. The larva eventually attaches to a hard surface and develops into a polyp.
Swimming larvaThe polypbuds to release young medusas.
Adult medusas reproduce sexually by releasing gametes intothe water.
Jellyfish Life Cycle
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Jellyfish
• class Scyphozoa (cup animal)
• life is spent mostly in medusa stage
• larva and polyp stage are usually the same
• reproduce sexually
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Hydras
• class Hydrozoa• usually grow in
colonies• no medusa stage in
life cycle of freshwater hydras
• may reproduce either sexually or asexually
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Anemones and Corals
• class Anthozoa (flower animals)
• only have a polyp stage in their life cycle
• many are colonial• reproduce sexually
(some asexually)• larva forms a new
polyp
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