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Chordates! Subphylum Urochordata Subphylum Cephalochordata Subphylum Vertebrata (focus)

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Presentation on theme: "Chordates! Subphylum Urochordata Subphylum Cephalochordata Subphylum Vertebrata (focus)"— Presentation transcript:

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

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 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 Jawless Vertebrates No paired appendages or hinged jaws!

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 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 Chapter 34: Vertebrate Evolution & Diversity 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 Fishes

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 Chapter 34: Vertebrate Evolution & Diversity “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 Fishes:

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 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 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 Frog Terrestrial carnivore Lungs; ear-drums No lateral line system No tail External fertilization; require water for eggs Currently, in rapid state of decline Acid rain; pathogens; habitat loss


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