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Chordata I. Chordate Characteristics A. Four characteristics must be present at some time in life. 1. Notochord - long flexible rod along dorsal side - provides simple skeleton in invertebrates - vertebrates retain only remnants Chordate Characteristics cont’d 2. Dorsal hollow nerve cord – neural tube - develops from plate of ectoderm - dorsal to notochord 3. Pharyngeal gill slits - embryonic slits by pharynx - filter feeding device in invertebrates - gas exchange in vert. 4. Muscular postanal tail B. 3 Subphyla 1. Urochordates – tunicate – invertebrates larval form has all 4 chordate traits Subphyla cont’d 2. Cephalochordates – lancelet – invertebrates segments formed from blocks of mesoderm called somites (seen in many embryos) Subphyla cont’d 3. Vertebrates II. Vertebrate Characteristics 1. 2. Highly cephalized – well developed brain Formation of neural crest – band of cells that pinch off neural tube and migrate throughout body to help in formation of other structures Vertebrate Characteristics cont’d 3. Vertebral column - skeletal unit that enclose nerve cord - axial skeleton – cranium, vert. column, ribs, sternum - appendicular skeleton – supports two pair of appendages 4. Closed circulatory system with ventral heart III. 2 Superclasses of Vertebrates Superclass Agnatha – jawless fish Superclass Gnathostomata – divided into Gnathostomata I and Gnathostomata II - Gnathostomata I Class Chondricthyes – cartilage fish Class Osteicthyes – bony fish Superclasses cont’d - Gnathostomata II – Tetrapods - Amphibians – link to land & water - Amniotes – Reptiles, Aves, Mammals IV. Detailed Chordate Classes A. Agnatha pg. 685 - no jaw, circular mouth w/teeth - notochord persists for life - 2 chambered heart (as in all fish) - ectothermic (cold-blooded) - lack paired appendages - lampreys & hagfish B. Chondricthyes - cartilage fish - sharks, rays, skates - hinged jaw w/teeth, anterior & ventral - notochord replaced by cartilage vertebrae - gill slits present Chondricthyes cont’d - stays buoyant by oil in liver & continuous swimming - acute senses including lateral line (row of organs sensitive to changes in water pressure) Chondricthyes cont’d Internal fert. – male has claspers to transfer sperm into female rep. tract 3 ways young are developed - oviparous: lay eggs that hatch outside mothers body - ovoviviparous: retain fert. egg in oviduct, nourished by egg yolk then hatch in uterus - viviparous: young develop in uterus & nourished by a placenta C. Osteicthyes Hinged jaw w/anterior mouth Osteicthyes cont’d Notochord replaced by calcium phosphate – vertebrae Gills covered by operculum (protective flap) allows fish to stand still Osteicthyes cont’d Swim bladder provides buoyancy Lateral line Skin glands secrete mucus 3 subclasses of Osteicthyes 1. 2. 3. Ray-finned fish Lobe finned fish Lung fish Ray-finned Very maneuverable fins Perch, bass, most familiar fish Supported by flexible rays for defense & movement Lobe-finned Rounded fin to prop up body Only one species left - Coelocanth Freshwater Lungs & gills Bottom dwellers – used pelvic & pectoral fins to “walk” Gave rise to amphibians Lungfish No gills, only lungs Similar to lobe-finned 3 kinds alive Live in stagnant ponds, swamps Come up and gulp air into lungs Burrow into mud in dry season (type of hibernation) D. Amphibia Descended from lobe-finned fish 350 mil. yrs. ago “2 lives” – refers to metamorphosis egg tadpole adult Most stay near water External fert. with much variety in egg carrying Many show complex & diverse social behavior E. Reptiles Scales w/keratin waterproof the skin Well developed lungs Ectothermic – behavioral adaptations help control body temp. 3 ½ chambered heart – beginning of septum Reptiles cont’d Internal fert leads to development of amniote egg pg. 693 - amnion – protection - chorion – gas exchange and protection - allantois – wastes, gas exchange - yolk sac – food supply Age of Reptiles 250-300 mil. yrs. ago Plants & insects already here for food Extinction of dinosaurs 65 mil. yrs. ago Aves link to reptiles Fossil of Archaeopteryx - clawed forelimbs w/scales - teeth - long tail w/vertebrae - feathers – endothermic? - weak flyer – small sternum - tree dwelling glider? F. Aves Birds Endothermic Amniote egg Scales of legs (keratin) 4 chambered heart Layer of fat insulates some Aves cont’d Adaptations for flight - wings & large sternum - strong pectoral muscles - feathers (keratin laced) - toothless - one ovary - honey-combed bones - lungs & air sacs G. Mammalia Mammary glands Hair laced with keratin Endothermic 4 chambered heart Diaphragm Most bear live young – viviparous 3 Subclasses 1. Monotremes – egg laying - eggs hatch hours after they’re laid - no nipples – milk secreted from glands, young sucks milk from fur - duck-billed platypus, spiny anteater 3 Subclasses cont’d 2. Marsupials – pouched mammals - young climb into pouch after birth to finish development - kangaroo, oppossum 3 Subclasses cont’d 3. Placental mammals - bear live young that have been nourished by a placenta - most mammals