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

atrial opening (water that passed through pharynx leaves this way) 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 Two sets of Hox genes 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