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Chordata Phylum Chordata • • • • • • Bilateral, Deuterostomate development Notochord Dorsal hollow nerve cord Pharyngeal slits Muscular Post-anal tail Segmented musculature – Repeating units called somites Chordate features • • • • • Oldest group ( ancestral) Urochordata The Tunicates, Sea Squirts Chordate Features found in larval phase Aid in dispersal, adults are sessile. Today’s sessile tunicates are derived trait Chordate Phylogeny Subphylum Urochordata • Only larva has chordate characteristics #63-x-section #65 Tunicates Tunicate larvae Tunicates nerve cord notochord gut oral opening atrial opening (water that passed through pharynx leaves this way) pharynx with gill slits Fig. 24.3, p. 385 Subphylum Cephalochordata • Come about by Paedogenesis (?) • Precocious sexual maturity in larvae • Adults now have all the chordate traits, and are motile • The lancelets have only a slight swelling , “anterior ganglia’ brain? Subphylum Cephalochordata # 66 Amphioxus Chordate Phylogeny Subphylum Craniata • Cephalized Chordates – Brain, eyes, etc. – Skull • Two sets of Hox genes • Neural Crest – – Infolding of ectoderm – Cells spread through developing body – Form neurons and other features • Teeth, facial bones, • Pharanygeal slits paired with muscles & nerves that pump water through slits • More active metabolism Class Mixini Jawless craniate • Mixini – the hagfishes (not a fish) – Have cartilagnous, skull and notochord Super Class - Vertebrata • More extensive skull • Backbone composed of vertebrae • Originally prongs of cartilage dorsally along nototchord protecting nerve chord • Later took over mechanical role of notochord • Later fins and other appendages form along vertebrae Chordate Phylogeny Class Cephalaspidomorphi • Lampreys • Have cartilaginous vertebrae-like extensions along notochord • Still jawless Gnathostomes • • • • Vertebrates with true jaws Additional Hox gene cluster Larger brains, better sense of smell sight Lateral line system to sense water movement • Mineralized endoskeleton • Two sets of paired appendages. • these paired appendages first functioned in swimming. • In tetrapods, the appendages are modified as legs on land. Class Chondrichthyes What’s New in Bony Fish • Bony Skeleton • Single Gill Opening – Operculum bellows water over gills • Swim bladder – gas from blood fills bladder, released to control buoyancy Swim Bladder Muscular Valve Gas Gland Lobed-finned fish vs. Amphibian Bones Class Amphibia REPTILIA - Amniotes MAMMALS Monotremes • • • • Warm blooded Have hair Lay eggs Young hatch and live outside mother • Make milk in glands, no nipples Marsupials • Live birth to underdeveloped young. Placenta forms, but not a long a time. • Young crawl to pouch • Physically attach to nipple in pouch and feed off milk, finish development while nursing. • Stay with mother in pouch until able to survive outside Eutherian mammals • “Placental mammals”- live birth • Young held inside past egg feed development • feed trough an umbilical attachment to the placental • Born more developed than marsupials • Feed off milk from breast- Not physically attached to nipple
