Chordata

Phylum Chordata

• Bilateral, Deuterostomate development

• Notochord

• Dorsal hollow nerve cord

• Pharyngeal slits

• Muscular Post-anal tail

• Segmented musculature– Repeating units called somites

Chordate features

• Oldest group ( ancestral) Urochordata

• The Tunicates, Sea Squirts

• Chordate Features found in larval phase

• Aid in dispersal, adults are sessile.

• Today’s sessile tunicates are derived trait

Chordate Phylogeny

Subphylum Urochordata

• Only larva has chordate characteristics

#63-x-section #65

Tunicates

Tunicate larvae

Tunicates

Fig. 24.3, p. 385

nerve cord notochord

gut

oral opening

atrial opening (water that passed through pharynx leaves this way)

pharynx with gill slits

Subphylum Cephalochordata

• Come about by Paedogenesis (?)

• Precocious sexual maturity in larvae

• Adults now have all the chordate traits, and are motile

• The lancelets have only a slight swelling , “anterior ganglia’ brain?

Subphylum Cephalochordata

# 66

Amphioxus

http://biodidac.bio.uottawa.ca/Thumbnails/showimage.cfm?File_name=CEPL004C&File_type=GIF

Chordate Phylogeny

• Cephalized Chordates– Brain, eyes, etc.– Skull

• Two sets of Hox genes• Neural Crest –

– Infolding of ectoderm– Cells spread through developing body– Form neurons and other features

• Teeth, facial bones,

• Pharanygeal slits paired with muscles & nerves that pump water through slits

• More active metabolism

Subphylum Craniata

Jawless craniate

• Mixini – the hagfishes (not a fish)– Have cartilagnous, skull and notochord

Class Mixini

Super Class - Vertebrata

• More extensive skull

• Backbone composed of vertebrae

• Originally prongs of cartilage dorsally along nototchord protecting nerve chord

• Later took over mechanical role of notochord

• Later fins and other appendages form along vertebrae

Chordate Phylogeny

ClassCephalaspidomorphi

• Lampreys

• Have cartilaginous vertebrae-like extensions along notochord

• Still jawless

Gnathostomes• Vertebrates with true jaws• Additional Hox gene cluster• Larger brains, better sense of smell sight• Lateral line system to sense water

movement • Mineralized endoskeleton• Two sets of paired appendages.

• these paired appendages first functioned in swimming.

• In tetrapods, the appendages are modified as legs on land.

Class Chondrichthyes

What’s New in Bony Fish

• Bony Skeleton

• Single Gill Opening – Operculum bellows water over gills

• Swim bladder – gas from blood fills bladder, released to control buoyancy

Swim Bladder

Gas Gland

Muscular Valve

Lobed-finned fish vs. Amphibian Bones

Class Amphibia

REPTILIA - Amniotes

MAMMALS

Monotremes

• Warm blooded

• Have hair

• Lay eggs

• Young hatch and live outside mother

• Make milk in glands, no nipples

• Live birth to underdeveloped young. Placenta forms, but not a long a time.

• Young crawl to pouch• Physically attach to nipple in pouch

and feed off milk, finish development while nursing.

• Stay with mother in pouch until able to survive outside

Marsupials

Eutherian mammals

• “Placental mammals”- live birth

• Young held inside past egg feed development

• feed trough an umbilical attachment to the placental

• Born more developed than marsupials

• Feed off milk from breast- Not physically attached to nipple