Chordates!

1. Chordates! Subphylum Urochordata Subphylum Cephalochordata Subphylum Vertebrata (focus)

2. Evolutionary relationships and HOX genes

3. Phylum Chordata: 4 key features**Each appears in a least one life stage

4. Phylum Chordata: 4 key features**Each appears in a least one life stage • 1) Notochord: • Longitudinal flexible rod made of fluid-filled cells in fibrous tissue • Dorsal • Underlies nerve cord • Replaced by jointed skeleton in the vertebrates • 2) Dorsal, Hollow Nerve Cord: • Derived from ectoderm • Develops into central nervous system (brain/spinal cord) • 3) Pharyngeal Gill Slits: • Slits in pharynx allowing for water efflux • Multiple functions in vertebrates (e.g. gills in fish) • 4) Muscular, Post-anal Tail: • Skeletal elements / muscle for mobility

5. Subphylum Urochordata: the tunicates • Invertebrates (notochord but no vertebral column) • Larva has all five chordate features • Adults retain only the pharyngeal slits • Expanded pharynx works similarly to the ctenidium of a mussel…

6. Subphylum Cephalochordata: the lancelets • Invertebrates (notochord but no vertebral column) • Larva has all chordate features • Adults retain all chordate features • Neoteny (paedogenesis) of a urochordate-like larva? • Muscles develop from somites: Blocks of mesoderm (segmented) • Feed similarly to the Urochordata

7. Plus paired appendages (2 pair) Cranium formed from neural crest cells Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands)

8. Craniata • Pronounced cephalization • Nerve tube/Neural crest • Ectoderm folds to form neural tube (nervous system) • Neural crest = ectodermal cells slough off neural plate to form some skeletal elements (e.g. cranium)

9. Living Craniata • Class Myxini: hagfish! • Has a cranium • Has a notochord • Feeding: secrete copious amounts of enzymatic slime to digest prey!

10. Subphylum Vertebrata • Features shared with Craniata • Neural crest • Pronounced cephalization • Derived character (above Craniata) • Vertebral column and skull • Protect spinal cord /brain • provide support • allow for fast movement • Composed of bone and/or cartilage; can grow with animal

11. Jawless Vertebrates No paired appendages or hinged jaws! Class Cephalaspidomorphi(Lamprey – 35 species): • Notochord present with cartilaginous projections that partially enclose nerve cord (origination of vertebral column) • Marine / freshwater parasites • Bore hole into prey; drink body fluids

12. Placoderm Branchpoint: above the jawless fish • Mineralized (ossified) skeleton and teeth • Paired appendages • Differential expression of Hox genes • Allow for effective maneuvering • Jaws • Modifications of skeletal rods of gill slits • Remaining gill slits function in respiration

13. Plus paired appendages (2 pair) Cranium formed from neural crest cells Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands)

14. Chapter 34: Vertebrate Evolution & Diversity Fishes Class Chondrichthyes(Sharks / Rays / Ratfish – 750 species): • Well-developed jaws and paired fins • Flexible endoskeleton composed of cartilage • Do have mineralized granules & bony teeth • Plus tooth-like scales • Ancestors were bony (secondarily lost) • Feeding • Suspension-feeders (whale sharks) • Carnivores (most others) • Acute vision & smell • Can detect electrical fields • Lateral line system (∆ water pressure) • Internal fertilization: • Some bear live young • In utero cannibalism occurs

15. Evolutionary relationships • Branchpoint above Chondrichthyes: • Development of lungs and lung derivatives (swim bladder) • Functions…

16. Plus paired appendages (2 pair) Cranium formed from neural crest cells Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands)

17. Chapter 34: Vertebrate Evolution & Diversity Fishes: “Class” Osteichthyes(Bony fishes – 30,000 species): • Most numerous vertebrate group (individuals / species) • Ossified endoskeleton (calcium phosphate matrix) • Flattened, bony scales • Mucus glands in skin = sliminess • Lateral line system • Operculum: Protective covering over gills • Operculum pumping • Swim Bladder: Air sac controlling buoyancy • Evolved from balloon-like lungs • Appear to have evolved in freshwater

18. Plus paired appendages (2 pair) Cranium formed from neural crest cells Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands)

19. Chapter 34: Vertebrate Evolution & Diversity Branchpoint: Tetrapods • Two pairs of leg-like appendages • Allowed for crawling through dense vegetation • Evolved from specialized fishes inhabiting shallow water • Benefited from food abundance &limited competition Acanthostega: A devonian tetrapod fish

20. Aquatic herbivore Gills Lateral line system Long, finned tail Tadpole Chapter 34: Vertebrate Evolution & Diversity Amphibians: Class Amphibia(450 species): • Salamanders, Frogs and Caecilians (legless) • “Amphibian” = Two lives (metamorphosis) Terrestrial carnivore Lungs; ear-drums No lateral line system No tail Frog • External fertilization; require water for eggs • Currently, in rapid state of decline • Acid rain; pathogens; habitat loss