Lecture'20'Bio'200''Deuterostomes:'o Far'fewer'dueterstomes'than'protostomes''o Human’s'closest'relatives'o Largest'animals'in'the'world'o This'groups'is'represents'half'of'bilaterians'o The'protostomes'have'much'more'diversity'though.'o Contain'3'major'groups:''o Echinoderms'o Hemichordates'o Chordates'(includes'lancelets,'tunicates,'vertebrates)'o One'major'difference'between'dueterstomes'and'protostomes'has'to'do'with'early'development.'In'the'dueterstomes,'the'mouth'developed'opposite'of'the'blastopore.'The'mouth'develops'second.'The'blastopore'develops'into'the'anus'first.'o All'of'the'organisms'triploblasts,'coelomates,'internal'skeletons''o Some'dueterstomes'are'segmented,'but'the'segments'are'internal'and'less'obvious'than'the'annelids'and'arthropods'o Monophyletic'group'o Fossils'of'extinct'deuterostomes'have'traits'that'are'found'in'the'echinoderms'and'chordates.'We'call'these'extinct'deuterstomes'homalozoans.'o Most'of'them'had'skeletons'that'are'skeletons'that'are'similar'to'modern'echinoderms'but'their'pharyngeal'gill'slits'and'their'symmetry'is'more'like'chordates.''o These'shared'traits'indicate'that'the'echinoderms'and'the'chordate'groups'were'likely'branched'apart'after'the'homalozoans,'and'their'morphology'diverse'from'that'point'on'until'the'modern'forms'became'into'being.'''Pharyngeal'gill'slits/archsT'o All'chordates'have'these'o Also'humans'have'it'o Filter'feeding'organs'found'in'the'Hemichordates'and'in'the'non'vertebrate'chordates'that'live'in'chordate'environments'today'o In'the'evidence'from'the'fossil'record,'the'earliest'dueterstomes,'were'not'only'bilateral'symmetric'animals,'but'they'also'had'several'pairs'of'external'gills'through'which'water'flows.''o In'the'modern'deuterstome'animals,'these'pharyngeal'gill'slits,'resembling'gill'slits,'they'are'at'some'stage'of'life'found'in'all'the'chordates'o All'the'vertebrate'embryos'develop'them'at'an'early'stage,'almost'certainly'vestigial'remnants'of'these'slits'or'archs'of'our'fishy'ancestors'that'develop'into'gills'that'we'see'in'fish'today.'o In'humans,'they'appear'in'later'developmental'stages'and'transform'into'other'parts'of'the'body'including'the'jaw,'the'middle'ear,'and'larynx.'''EchinodermsT''o First'deuterostome'o As'the'largest'group'other'than'the'chordates,'they'are'fairly'closely'related'to'humans'o The'connection'between'the'chordates'and'echinoderms'all'has'to'do'with'development,'not'intelligence'or'body'form'o The'tight'relationship'between'these'very'different'looking'groups'is'actually'a'clear'example'of'how'basic'morphology'doesn’t'always'make'evolutionary'relationships'clear.'o Pentaradial'symmetry'means'there'are'five'axes'of'symmetry'o Ex:'starfish,'Sand'dollar,'starfish'larvae'o All'echinoderms'are'radial'symmetrically'as'adults,'special'symmetry'with'only'5'axis,'instead'of'infinite'number'o Even'if'there'has'been'a'reversion'of'the'radial'symmetry,'we'kno'the'echinoderms'are'not'related'to'basal'radial'groups'o The'complex'organs'of'echinoderms'mark'them'a'very'diverse'animals'as'does'their'dueterstomic'development.''o They'have'3'tissue'layers'o Bilaterial'larvae'stages'of'the'starfish,'show'close'connection'to'the'bilaterians.''o 'The'echinoderms'are'characterized'by'an'internal'skeleton'o They'grow'just'like'humans'o This'skeleton'is'made'up'of'hard'endoskeletal'plates,'this'winds'up'acting'like'a'shell.'o This'skeleton'made'of'calcium'salts'and'proteins'is'inside'but'usually'covered'by'a'very'thin'skin'unlike'human'skeletons'which'is'much'deeper'in'out'bodies.'o The'echinoderms'mean'spiny'skin'o The'endoskeleton'is'covered'with'neurosensory'cells,'which'allows'these'animals'to'experience'the'world'around'them'o They'have'this'unique'internal'system'that'involves'the'pumping'of'water'into'specialized'systems,'called'water'vasculature'system.'''''o Water'filled'canals'called'tube'feet'that'lead'to'extensions'from'the'body'o The'same'system'is'used'for'feeding'and'gas'exchange'and'locomotion'o Seawater'enters'the'echinoderm'body'through'a'small'hole'or'a'pore'called'a'Madreporite''o Then'water'flows'into'a'structure'called'the'ring'canal'and'then'to'cana l s't ha t'radiate'into'each'of'the'“arms”'into'the'body'connecting'into'the'tube'feet.'o Food'can'be'removed'from'the'flowing'water'and'the'force'of'the'water'moving'through'the'system'can'work'like'a'hydrostatic'skeleton'o The'tube'feet'is'also'used'for'attachment'o Not'bilateral,'meaning'headless.''o No'dorsal'or'ventral'part'of'starfish,'instead'we'tal k'about'the'oral'surface'(underneath),'what'they'crawl'on'o The'other'side'is'called'aboral'surface.'o Special'form'of'asexual'reproduction'which'is'a'form'of'regeneration'just'like'in'the'sponges'o Many'echinoderms'can'regenerate'lost'parts'like'sponges.'o Some'cases,'a'limb'launch'itself'from'the'main'body'and'grow'into'a'new'organism.''o The'original'animal'will'then'regenerate'the'lost'limb''o Some'species'will'drop'various'parts'while'under'attack,'and'later'regrow'them'o Some'species'can'even'break'in'half'and'each'half'can'survive'regenerating'the'missing'pieces.'o Despite'this'ability,'most'echinoderms'reproduction'is'sexual'o The'sexes'are'separate,'but'sexual'dimorphism'is'rare.'o The'gametes'are'usually'released'into'the'water'and'externally'fertilized.''o More'than'20'extinct'classes'of'echinoderms,'but'only'3'extant'groups:'o 'CrinoidsT'sea'lilies,'feather'stars'• made'up'of'two'types:'Sea'lilies'(anchored),'and'feather'stars'(free'swimming)'• many'arms,'unusually'shaped'• Sea'liliesT'attaches'to'surface'with'flexible'stalk'and'don’t'typically'move,'the'main'body'is'a'cup'that'contains'the'water'vasculature'system.'5'to'several'hundred'arms'will'radiate'from'this'cup.'• These'arms'contain'tube'feet'which'will'take'in'food'from'the'water.'• Ex:'Nominus'novus'• The'Feather'Stars'are'similar:'attatch'themselves'to'the'surface'with'their'flexible'arms'that'allow'for'some'limited'movement'• EX:Oxycomanthus'bennetti'''o 'EchinozoansT'sea'urchins,'sand'dollar,'sea'cucumbers'• Include'sea'urchins,'sand'dollars,'and'sea'cucumbers'• 'Don’t'look'like'most'echinoderms'because'it'is'hard'to'see'pental'radial'symmetry'because'no'arms'• 'The'sea'urchins'look'spherical,'but'hemispherical'because'they'have'a'flat'underside.'• Covered'with'spines'that'are'attached'to'u
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