1. Origin of the Vertebrates

2. Early recognition that this forms a related grouping, based on certain characteristics in common: internal skeleton, circulation direction, some segmentation, etc.

3. Agnatha (no jaw) = most primitive as no jaw, no paired appendages, and only 2 semicircular canals, not three. Considered vertebrate as it has vertebrae = segmented backbone of either cartilage (here) or bone Also, dorsal nerve cord, other features.

4. Fossil Agnatha: no jaw, poor paired appendages, some with none, and 2 semicircular canals But: have bone as body armor and are filter feeders

6. 2 semicircular canals in inner ear Gills for filter feeding and respiration No jaws Odd nerve area = electric sensitivity?

8. Seeking ancestors or relationships The great split among higher animals: deuterostome or protostome

10. Clevage pattern

11. Other major differences Determinate vs intedeterminate clevage Origin of coelom (schizocoel = protostome enterocoel = deuterostome Origin of mesoderm- outpocket, vs 4d cell mesoderm skeleton(deutero) vs ectoderm skeleton (protostomes)

12. The other major Deuterostome group = Echinoderms spiny skin, pentaradiate, etc,

13. Fossils include sea lillies = filter feeders. Sessile. All living ones have a bilateral larvae, and are deuterostomes.

14. Amphioxus Other forms related to Vertebrates

15. Has segments, gills, dorsal nerve cord, also a notochord, Odd in no brain, segmented gonads, etc.

16. Why these features? Nerve cord – coordination of movement Notochord – organizer for the nerve cord Gills – here for feeding, only later for respiration.

17. So new group = Phylum chordata Includes subphylum Vertebrata Includes “odd” groups with notochord, nerve cord and gills. = amphioxus, tunicates,

18. Tunicate

19. Note: origin of visceral- somatic dichotomy Visceral = adult Somatic = larval tail origin of need for dorsal nerve cord, notochord Tunicate and larvae

20. Neoteny = keep immature features into adult Paedogenesis = become an adult Earlier in life Adult = can reproduce