Lecture_11_14_Cnidaria

Lecture_11_14_Cnidaria - No symmetry, 1 cell layer...

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Hox genes? No symmetry, 1 cell layer Motile Multicellular Heterotroph
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Diploblasts: Ctenophores and Cnidarians
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Ctenophora: Comb jellies Your basic comb jelly: 100 species, open ocean predators.
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Cnidaria
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Major Innovations in Cnidaria 1. Diploblastic: ectoderm and endoderm 2. Radial symmetry 3. Muscle cells, nerve cells 4. Cnidocytes that house nematocysts 5. Dimorphic body plan (medusa and polyp) 6. Light sensitive organs
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…The truth is, however, many cnidarians are very effective predators that are able to kill and eat prey that are much more highly organized, swift, and intelligent. They manage these feats because they possess tentacles that bristle with tiny, remarkably sophisticated weapons called nematocysts… [the nematocyst] achieves a velocity of 2 meters/second and an acceleration of 40,000 X gravity, it instantly penetrates its prey and injects a paralyzing toxin…Some nematocysts threads can penetrate human skin causing sensations ranging from minor irritation to great pain, even death…A nematocyst is a fearsome, but wondrous, tiny weapon. (Hickman et al., 2008)
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Diploblastic organization (Ectoderm & Endoderm)
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Muscle bands Of an anemone
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Neurons, nerve net Hydra neuron and Nerve net Nerve net of a Hydrozoan medusa
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Cnidocytes and Nematocysts synapomorphy and key innovation for cnidarians Concentrated in tentacles, can shoot once only
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Medusa: floating/free-swimming Polyp or hydroid: sessile
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with or without sexual reproduction Obelia sp. (hydrozoan)
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Lecture_11_14_Cnidaria - No symmetry, 1 cell layer...

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