Ward_Lect34A_Chordata_ppt

Ward_Lect34A_Chordata_ppt - BIS2C Winter 2009 (Ward)...

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BIS2C Winter 2009 (Ward) Lecture 34. Chordata, Part 1 Today's lectures (11 March) finish Echinodermata introduction to Chordata major features early chordate evolution origin of vertebrates jawless and jawed fish Tetrapoda, especially amniotes convergent evolution
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California sea otters eat urchins. Sea urchins consume kelp. When sea urchins are abundant they can destroy underwater kelp forests.
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Sea otters can be considered a “keystone species” in this system because 1. The kelp forests flourish when they are removed. 2. Their presence or absence has a large effect on ecosystem structure. 3. They provide the key to understanding why sea urchins eat kelp. 4. Their abundance is positively correlated with the abundance of other animals in the environment. 5. They have evolved to eat sea urchins.
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Sea cucumbers (Holothuroidea) soft-bodied and slug-like (ossicles much reduced) greatly elongated oral/aboral axis, secondarily bilateral grazers, suspension feeders
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Sea cucumbers (Holothuroidea) can expel parts of their gut as anti-predator defense ( http://www.youtube.com/watch?v=lKWSLg5PDiU ) Sea cucumber with expelled Cuvierian tubules
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What are chordates? Sea squirts, lancelets, jawless fishes, jawed fishes, and tetrapods (amphibians, reptiles, mammals) Diverse (and often dominant) group of animals, both on land and in water.
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What are chordates? Deuterostomes with… 1. Notochord 2. Dorsal hollow nerve cord 3. Postanal tail 4. Pharyngeal slits
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What are chordates? Deuterostomes with… 1. Notochord 2. Dorsal hollow nerve cord 3. Postanal tail 4. Pharyngeal slits at least in embryo
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Other important innovations arose within chordates including… 1. Internal skeleton with vertebrae 2. Jaws 3. Two pairs of walking limbs
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This document was uploaded on 04/02/2009.

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Ward_Lect34A_Chordata_ppt - BIS2C Winter 2009 (Ward)...

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