BIOL 112 Lecture 32

« previous | Friday, November 16, 2012 | next »

Chapter 34: Vertebrates

Phylum Chordata (invertebrates)

• Lamprey
• Tunicate
• Hagfish

Largest organisms

• terrestrial: dinosaurs
• ever: blue whale

Characteristics of Chordata — present in all chordates at some stage in life (e.g. at development)

• Notochord
• Dorsal Hollow Nerve Cord (neural tube formed from ectoderm invagination)
• Pharyngeal Slits or Clefts (feeding in aquatic invertebrates, gas exchange in aquatic vertebrates, ear and jaw in terrestrial vertebrates)
• Muscular post-anal tail

Notochord

• Mesoderm-derived tissue (just like muscle)
• Runs along anterior-posterior axis
• Dorsal side of animal

Functions:

• developmental: (all chordates) secretes growth factors that organize surrounding tissues
• (invertebrates only) functions as an axial skeleton in absence of vertebrae. c.f. vertebrates, where notochord is transient (lost in later stages)

Chordata: Cephalochordata

lancelets: an invertebrate chordate

Suspension feeders that bury themselves in sand.

pharyngeal slits used to filter food particles

Enlarged anterior dorsal nerve cord (rudimentary brain)

Craniates

Chordates with a head (brain + skull)

Neural crest cells migrate to form other parts of the head

Example: Hagfish

not a fish

• Has a brain that is covered by a cartilaginous skull cap
• Notochord is kept as endoskeleton
• No jaws
• Teeth made of keratin
• Slime glands (ewww!)