Chordates! Subphylum Urochordata Subphylum Cephalochordata Subphylum Vertebrata!

Evolutionary relationships and HOX genes

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

 Notochord:  Longitudinal, flexible rod: fluid-filled cells in fibrous tissue  Dorsal  Underlies nerve cord  Replaced by jointed vertebral column in the vertebrates  Dorsal, Hollow Nerve Cord:  Derived from ectoderm  Develops into CNS (brain / spinal cord)  Pharynx with gill slits:  Slits in pharynx allowing for water efflux  Multiple functions in vertebrates (e.g. gills in fish)  Muscular, Post-anal Tail:  Skeletal elements / muscle for mobility  “Fifth” Feature = endostyle or thyroid gland…

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…  Cilia and mucus!

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 from somites: Blocks of mesoderm (segmented)  Feed similarly to the Urochordata

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

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)

Living Craniata  Class Myxini: hagfish!  Has all chordate features  Additionally, has a cranium  Feeding: use rasping teeth to feed on soft tissue (from the inside out!)  Slime: anti-predator

Subphylum Vertebrata: The vertebrates!  Features shared with Craniata  Neural crest cells  Pronounced cephalization; cranium  Derived characters (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

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!

Placoderm Branchpoint: above the jawless fish  Mineralized (ossified) skeleton and teeth  Paired appendages  Differential expression of Hox genes  Allow for effective maneuvering  Jaws  From skeletal rods of anterior gills

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

Chapter 34: Vertebrate Evolution & Diversity Class Chondrichthyes (Sharks / Rays / Ratfish – 750 species) : Well-developed jaws and paired fins Flexible endoskeleton composed of cartilage Appear after branchpoint for mineralized bone (ancestors bony!) Do have mineralized granules & bony teeth, tooth-like scales 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

Evolutionary relationships  Branchpoint above Condrichthyes  Development of lung and lung derivatives (i.e. swim bladder)  Functions? (Know!)

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)

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:

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

 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 Branchpoint: Tetrapods

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