CC BIO 44 - The Deuterostomes Lecture Notes

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The DeuterostomesSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8The ChordatesSlide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24How to become a better fishSlide 26Slide 27Fin typesSlide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45The DeuterostomesOrigin of vertebratesAnd the evolution of “fish”Chordates (including vertebrates) and EchinodermsBasic deuterostome characteristics(vs Protostome)Radial vs spiral clevageMesoderm formation 2nd opening into gastrula = mouth not firstEchinoderm variationSea lilies; marine, sessile, filter feeders, external sieves.The Chordates•Have a dorsal nerve cord (sometime)•Have a notochord = dorsal stiffening rod retained in adult vertebrates as organizer for dorsal nerve cord•Have gills or pharyngeal cleftsAll three features are organizers for later development – so are retained in embryos.Why these features?Nerve cord – coordination of movementNotochord – organizer for the nerve cord Gills – here for feeding, only later for respiration.Agnatha: living = lamprey, hagfish,Scavengers and parasites. Agnatha – most primitive vertebrates: vertebrates: have notochord, dorsal nerve cord, gills primitive: no jaws, no paired appendages, 2 semicircular canals in ear.Vertebrates – a subset of chordates with a vertebral column.Fossil Agnatha: add bony armor; filter feeding.AmphioxusNon-vertebrate Chordates.No limbs, no jaws, gills a feeding device (become respiratory when armor added and skin respiration no longer possible. Also size increase means need something more than skin for respiration), but has a notochord, nerve cord and gills. Marine organisms.TunicateAnother non-vertebrate Chordate.Adult: filter feeder – basket of “gills”No nerve cord, no notochord, mostly eats and reproduces.Larvae – some have motile larvae = dispersal and ability to choose substrate.Note: origin of visceral- somatic dichotomyVisceral = adultSomatic = larval tail origin of need for dorsal nerve cord, notochordTunicate and larvaeLarvae has tail = notochord, nerve cord, muscles.Somatic organism = nerves, brain, muscle, tail,segmentation, notochord –voluntary nervous system = swimming portion of larvaVisceral organism = gut, reproduction, respiration = involuntary nervous system = adult portion of larvaNeoteny = keep immature features into adultPaedogenesis = become an adult Earlier in lifeAdult = can reproduceAgnatha (fossil ones)Armored – heavyTail asymmetricno jawsNot much paired appendagesInternal skeleton of cartilageSea scorpion; arthropod, up to 6 feet long. predatoryHow to become a better fish•Add paired appendages•Add jaws•Loose the armor•Strengthen internal skeletonArmored fishCartilaginous fishSpine finsBony fishJawless fishPaired fins allow stabilization and maneuverability.Fin types•Fin fold•Spiny fin•Ray fin•Fleshy finRay fin fleshy fin, fleshy fin symmetrical asymmetricalAgnatha with fin foldsShark with ray fintturnTTurn gills into jaws: what permits this?Gills become more efficient, not as many needed. Primitive fish – 7 gills, modern fish 3.5Class placodermi ; added jaws but still has armor on head and shoulders.shark skin = denticles = small teeth, = same structure as dermal armor of primitive fish and of our teeth – enamel on outside, dentine underneath, then bone.Class OsteichthyesTurn internal cartilage into bone during developmentReduce armor to thin scales.Note: dual origin of skeltonBlue and red = internal skeletonCartilage (blue) being replaced by bone (red)Pink – the skull is direct ossification, no cartilage precursor and is remnant of old dermal armor, protecting head and brain.Crossopterygian; sarcopterygian with fleshy


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CC BIO 44 - The Deuterostomes Lecture Notes

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