Chordates Notes

Origin and Evolution of VertebratesCh. 34

Chordate Characteristics: Present in embryos; not always in adults Notochord Flexible dorsal rod; endoskeleton works with muscles Dorsal, hollow nerve chord Tube forms from fold of ectoderm dorsal to notochord Pharyngeal slits or clefts Ancestral use: filter-feeding and gas exchange Sea -> mouth -> pharynx -> slits -> sea Muscular post anal tail Multiple muscle segments Undulating locomotionCephalochordata: Lancelets All key chordate features in adult Burrows tail-in and suspension feedsUrochordata: Tunicates (sea squirts) Highly derived sessile adult: suspension feeds with pharyngeal slits The tough tunic has cellulose Swimming larva has all key chordate features

Vertebrates Vertebrae of cartilage/bone Enclose spinal cord (dorsal nerve cord) In most, vertebral column replaces notochord as main body support Well-developed head Cranium (skull of cartilage or bone) Holds brain (coordination of voluntary and involuntary responses) Paired sensory organs Heart (2-4 chambers with valves) and closed circulatory system With hemoglobin in blood cells Ventricle = power push Gill arches/rods of cartilage or bone support gill slits Earliest vertebrates First verts all jawless, fishlike Sucked in food with help of gill arches No lateral fins Many later jawless fish had bony armor plates Some with lateral fins All extinct by mid Paleozoic, replaced by jawed fishes Jawless fish: myxini and petromyzontida Eliminating craniate clades* Extant jawless vertebrates Hagfish and lamprey (dorsal fins) Eel-like with no lateral fins Cartilage skull; no jaws Keratinous teeth aid in feeding Mostly use notochord; but spinal cartilages present also Myxini: hagfish Marine scavengers Reduced eyes ***slime*** defensive (threads and mucous) Petromyzondita: Lampreys Jawless parasite on a fish Keratinous teeth Most vertebrates have jaws Gnathostomes Gnathostome characteristics Vertebrates with jaws Derived from gill slit supports Usually have teeth (predation) Larger forebrain (smell and sight) Paired lateral fins/limbs (usually 2 pair) Pectoral and pelvic

ALL VERTEBRATES are chordatesTunicates and lancelets develop notochords but not skullsAnd are invertebrates