Lecture 19 - 1 Chordate Differences(four a Notochord fluid...

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1) Chordate Differences (four) a) Notochord- fluid filled cells in fibrous tissue- support i) Mineralized skeletal structure in most except two b) Dorsal nervecord Hollow because of folding of ectoderm c) Pharyngeal slits (clefts if not fully formed) in pharynx d) Post-anal tail 2) Some only present at certain stages, i.e. humans in embryo development (clefts) 3) Use echinodermata as outgroup- most related, deuterostome 4) Urochordate a) Chordate characteristics present as larvae, not adult b) Sessile filter feeders c) Water enters mouth into central cavity moves across pharynx out through pharyngeal slits lined with mucus which catches nutrients i) Water moves out through atrium out through excurrent cyphon 5) Cephalochordates a) Adults settle into sand, filter feed b) Tentacles that generate inflowing current, water out through pharyngeal slits c) Brain tough to find- swelling in posterior portion of nerve cord i) In development, 3 hox genes are expressed in posterior lancelet embryo nerve cord as are expressed in brain of vertebrate embryo, same spatial path- give rise to development of forebrain, midbrain, hindbrain 6) many evolutionary developments exhibit coordinated elements that work in coordinated way that give way to anatomical/physiological complexity 7) More sensory, need bigger brain, therefore would need protective case (think of these developments as highly coordinated) 8) Hagfish a) Neural crest cells form at dorsal side to posterior i) Give rise to jaws, facebones, skull b) Marine scavengers c) Have slime glands, when attacked, secrete several gallons of slime within a minute- clogs gills of attacker d) By head, talking about cranial structure, cartilaginous case 9) Lamprey a)
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