McRaeNotes - Rotifers & worms.pdf - BIOL 1200 Dr Susan...

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BIOL 1200Dr Susan McRae1ProtostomestriploblasticanimalsAcoelomate, Coelomate and Coelomate grades: evolution of body cavitiesacoelomate– Gr.a‘without’koilos‘hollow’have no cavity between digestive tract and outer body wallphylum Platyhelminthes, the flatwormscoelomates– withbody cavity– fluid-filled space between digestive tract and body walltruecoelom– fluid-filled body cavity completely lined with mesoderm-derived tissueinner and outer layers of tissue that surround body cavity connected bymesenteries which support internal organsProtostome-Deuterostome dichotomy among coelomatesProtostomes:mollusks, annelids, arthropods & othersDeuterostomes:echinoderms, chordates & othersThis division is based on developmental differences:Cleavagemany protostomes,spiral cleavage: planes of cell division are diagonal to the vertical axis of theembryodeterminate cleavage: fate of embryonic cells determined very early indevelopmentmany deuterostomes,radial cleavage: planes parallel and perpendicular to vertical axis of eggindeterminate cleavage: each cell produced early in cleavage divisions retainsability to develop into a complete embryo (e.g. identical twins,e.g. developmental versatility of‘stem cells’may hold the answer to treatmentof many conditions including Parkinson’s disease, Alzheimer’s, some cancersetc.)Coelom formationprotostome development isschizocoelous– as the archenteron forms, thesolid mass of mesoderm splits (Gr.schizo‘to split’) to form coelomic cavitiesdeuterostome development isenterocoelous –mesoderm buds from the wallof the archenteron and hollows forming coelomic cavitiesBlastopore fate(the opening of the archenteron)after the archenteron develops, a second opening forms at the opposite end ofthe gastrula –> the other end of the digestive tubemany protostomesmouth develops from first opening; Gr.protos‘first’stoma‘mouth’many deuterostomesmouth develops from second opening; Gr.deuteros‘second’blastopore forms the anus
BIOL 1200Dr Susan McRae22 Protostome clades:Lophotrochozoalopho-trocho-zoaLophophorate phylamany aresessilesuspension feeders (= filter feeders), almost all marineno distinct headu-shaped digestive tractnamed forlophophore= horseshoe-shaped circular fold of the body wall bearingciliated tentacles that surround the mouthcilia draw water toward mouth between tentaclestrap food particlesanus is outside the whorl of tentaclesPhyla with trochophore larvaesome animals havelarval stages –sexually immature forms, morphologically distinct

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Term
Fall
Professor
mcrae
Tags
Annelid, Dr Susan McRae

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