Wiens-lecture 9-14April_v2

Wiens-lecture 9-14April_v2 - Todays Lecture Phylogeny and...

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Today’s Lecture Phylogeny and diversity of ecdysozoans
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Test next Wednesday Same format and rules as previous exams Read the book and go over the lectures, but test will be primarily on the lectures
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Studying advice Big studying night should be the night before the night before the exam, but start before then also (e.g., Sunday) Don’t stay up all night the night before the exam Write down and then rewrite all the material in the lectures 5-6 times; don’t expect to memorize the material just by reading it Make flashcards to learn vocabulary; start this week, not next week Study alone, in a quiet place with no music or TV (try the library)
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Phylogeny of animals last Friday Monday Today Friday April 19–28
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Phylogeny of Protostomes
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Lophotrochozans vs. ecdysozoans Ecdysozoans share an exoskeleton (external skeleton) Secreted by epidermis, made of layers of protein and (in some groups) a strong waterproof polysaccharid called chitin Provides protection and support But has an important problem
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Lophotrochozans vs. ecdysozoans Ecdysozoans share an exoskeleton (external skeleton) Exoskeleton cannot grow To increase in size, individuals need to “molt” (shed) the exoskeleton, process called ecdysis New exoskeleton grows underneath the old one, expands and hardens after ecdysis
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Lophotrochozans vs. ecdysozoans Ecdysozoans share an exoskeleton (external skeleton) In worm-like ecdysozoans, exoskeleton may be thin, flexible Called cuticle A thin cuticle allows water, oxygen, and minerals to pass into the body, but restricts species to moist environments
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Lophotrochozans vs. ecdysozoans Ecdysozoans share an exoskeleton (external skeleton) Species with waterproof exoskeleton able to invade land and dry areas But hard to move (not flexible); body needs appendages Cannot breathe through skin; requires gas exchange system
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3 obscure groups of marine ecdysozoans • Priapulids • Kinorhynchs • Loriciferans
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3 obscure groups of marine ecdysozoans Priapulids 16 species, marine, 0.5 mm to 20 cm
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