Biology Notes 3-19-08

Biology Notes 3-19-08 - Biology Notes March 19, 2008...

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Biology Notes March 19, 2008 Hemichordates (acorn worms) -have three part body plan -proboscis -collar -trunk -capture prey with sticky proboscis and pulls it into mouth in collar -The pharynx opens to outside via pharyngeal slits, a site for gas exchange Chordates: All chordates have: -dorsal hollow nerve cord -a tail extending beyond the anus -a notochord -pharyngeal gill slits are present at some stage, but often lost as adult -the notochord is a core of large cells with fluid filled vacuoles making it rigid but flexible -muscular post anal tail used in swimming Urochordate -group is all marine -90% are ascidians Ascidians -Sea squirts or tunicates -adult body is bag-like and enclosed in a tunic secreted by the epidermis -filer feed with pharyngeal basket -larvae reveal the evolutionary relationships -both urochordates and vertebrates have all the chordate traits as larvae -metamorphose into sessile or tail-less adult Cephalochordates -lancelets -very small, less than 5cm -notochord is retained throughout life and is used in burrowing
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Biology Notes 3-19-08 - Biology Notes March 19, 2008...

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