Leader: Kirsten Karkow
Course: Biol 211 - Wilsey
Date: 2/20/2012
Worksheet 13
Supplemental Instruction
Iowa State University
List and describe the four characteristics common to all Chordates.
1. Notochord – long, flexible rod that provides axial support. NOT equivalent to the nerve
cord! (It isn’t a nerve, it’s an early backbone – support).
2. Dorsal, hollow nerve cord (as opposed to a solid, ventral nerve cord).
3. Pharyngeal slits – can be modified for feeding, respiration, or parts of head and neck.
4. Postanal tail (as opposed to an anus at the END of a “tail”, as in worms).
What are the three major groups within PHYLUM CHORDATA?
1. Cephalochordata (lancelets) – keep chordate characteristics into adulthood.
2. Urochordata (tunicates/sea squirts) – have chordate characteristics during larval stage.
3. Vertebrata
List and describe the four characteristics of the SUBPHYLUM VERTEBRATA.
1.
2.
3.
4.
Pronounced cephalization – formation of a head → skull + brain.
Vertebral column – replaced the notochord. Will encase and protect the nerve cord.
Closed circulatory system – blood is pumped through vessels (veins, arteries).
Separate males and females
NOTE: These are in addition to the chordate characteristics!
Development of Vertebrates
The following clades are listed in the order of development. Keep this in mind when studying!
Which characteristics developed when is important (hint, hint).
1. Craniates
o Named for the fact that they have a cranium.
o Includes hagfishes on.
 Hagfishes – slimy, blind fish that have a skull but no vertebrae.
2. Vertebrates
o Named for the fact that they have vertebrae.
o Includes lampreys on.
 Lampreys – jawless, appendage-less vertebrates. Parasites to other fish.
Supplemental Instruction
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3. Gnathostomes
o Named for the fact that they have jaws (think gnashing - chewing).
o Have vertebrae. This often replaces the notochord.
o Have paired appendages.
3a. Chondrichthyes
o Named for their cartilage skeletons (chondro = cartilage).
o Includes sharks and rays.
o First organisms to have jaws.
o Have internal fertilization.
o Maintain buoyancy through continuous swimming.
o Detect other animals via a lateral line – detects pressure waves.
3b. Bony Fishes
o Named for their bony skeletons (not cartilage).
o Have external fertilization.
o Maintain buoyancy through a swim bladder.
o Detect other animals via a lateral line.
o Includes First. Ray-finned fish – have ray fins (bone).
(4. Lobe Fins)
Second. Coelocanths – have lobed fins (bone + muscle).
Third. Lungfish – have lobed fins, plus gills AND LUNGS, so can live
in oxygen-poor water.
5. Tetrapods – animals with four legs. Legs developed from lobed fins of “fishapods”. Had to
adapt locomotion, reproduction, and prevent desiccation.
5a. Amphibia
o Named for the fact they live in two environments (need water for eggs and
larva, undergo metamorphosis).
o Includes frogs, toads, salamanders, caecilians.
o First vertebrates on land.
o Have external fertilization.
o Breathe via lungs + oxygen-absorption through skin.
o Have a 3-chambered heart.
6. Amniotes – animals that create an amniotic egg.
Amnion – sac to protect embryo
Yolk Sac – contains nutrients
Allantois – stores wastes
Albumin – egg white
Shell – PREVENTS DESICCATION! DON’T REQUIRE WATER (like amphibians).
6a. Reptilia
o Includes turtles, lizards & snakes, crocodilians, dinosaurs, and birds.
 Archaeopteryx – dinosaur fossil, original bird.
o Have scales of keratin to prevent desiccation. (Feathers = modified scales).
o Breathe via lungs.
o Are ectotherms. (Exception: birds are endotherms.)