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

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. No paired appendages or hinged jaws!
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. 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
Placoderm

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

14. Class Chondrichthyes (Sharks / Rays / Ratfish – 750 species):
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. Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands)
Cranium formed from neural crest cells
Plus paired appendages (2 pair)

17. “Class” Osteichthyes (Bony fishes – 30,000 species):
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. Notochord; Dorsal, hollow nerve tube; pharynx with slits, post-anal tail (with segmented muscle bands)
Cranium formed from neural crest cells
Plus paired appendages (2 pair)

19. Branchpoint: Tetrapods
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. Class Amphibia (450 species):
Chapter 34: Vertebrate Evolution & Diversity
Amphibians:
Class Amphibia (450 species):
Salamanders, Frogs and Caecilians (legless)
“Amphibian” = Two lives (metamorphosis)
Tadpole
Aquatic herbivore
Gills
Lateral line system
Long, finned tail
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