Chapter 2. Chordate CharacteristicsChapter 3. Vertebrate Story➔Chordatesoconsists of 3 groups1.Cephalochordates(amphioxi/lancets)2.Urochordates (tunicates / seasquirts)3.Vertebrates (fishes, amphibians,reptiles, mammals)oshare common fundamental bodyfeatures1.notochord2.pharyngeal slits3.endostyle (thyroid gland)4.dorsal hollow nerve cored–formingthe simple central nervous system5.post-anal tail➔Developmental Patterns of Chordates-processofreproductionthroughfertilization (fusion)oEgg and Fertilization-union of sex cells oof the samespecies→diploid zygote→developed zygote form intothemorula,blastulagastrula, and neurula-eggs can be considered as one ofthe largest cell in the body→→these cells are nourished bythe yolk→amount of yolk is dependenton the organism→usuallyproducedfromvitellogenin-uneven distribution of yolk willallow the polarity of the egg→2 poles allow one toidentify the region of theegg yolk and the region ofthe nucleus•vegetal pole-area with majority ofthe yolk component•animal pole-area with the nucleusegg•oviparous-lays egg•ovoviviparous-egg hatches inside theparent’s body-parent produces milk andegg•viviparous-noprotectiveshellproduced-developed offspring is bornoCleavage Formation and Blastulation-excessive amounts of yolk will hinderthe proper cleaving of the cell
•meroblastic cleavage-cleavage does not fully separatethe cytoplasm of the dividingcells•holoblastic cleavage-cleavage is able to successfullyseparate the cytoplasm•radial-in 8-cell stage, the upper layerof cells can be found sittingdirectly on top the lower layerof cells•spiral-in the 8-cell stage, the upperlayer of cells can be foundsitting at the spaces betweenthe cells of the lower layer•discoidal-a disc is formed during thecleavage formation which isfound on top of the yolk•blastula-transformed clump of numerouscells from zygote•blastomere-blastula that each individual ispresent in•blastocoel-fluid-filled cavity inside theblastula-during this stage, developing embryohas about a hundred to thousandsof cells each of which containsdifferent cytoplasmic compositionoGastrulation-pertains to the gut formationwherein the endoderm will producethe initial gut of the organism-responsible for the production of thegerm layers▪ectoderm▪endoderm•mesoderm-positioning of the cells in a gastrulawill give an idea about the eventualinteraction of each region-migration of cells in chordate groupsmay be one of the following:•epiboly–cells spread across theouter surface as a unit•involution–cells may turninward and then spread over theinternal surface•invagination–the wall of cellswill indent or fold inward•delamination–sheets of cellsmay split into parallel layers•ingression–individual surfacecells may migrate to the interiorof the embryooOrgans•protostomes-mollusks,annelids,andarthropods-where schizocoelus organism orschizocoelomates belong to•
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