Craniate Group

Question 1

What is the main added feature of chordate group craniate?

Answer 1

they have a head .. cranium … this developed separately from the arthropod heads

Question 2

What is an advantage of heads?

Answer 2

they provide better coordination of movements and complex feeding behaviours

Question 3

what are some characteristics about animals in this group?

Answer 3

• most of them have vertebrates, but some lack one like the myxini
• includes the largest animals ever lived like dinosaurs, and blue whales
• can be marine, freshwater or terrestrial

Question 4

what are the 5 derived character states present in craniates?

Answer 4

1. two or more clusters of hox genes (non craniates have one cluster) this results in greater genetic diversity
2. neural crest –> group of embryonic cells that form near the dorsal margins … this helps make bones and cartilages of the cranium
3. endoskeleton and pronounced cephalization –> brain is encased in skull and endoskeleton is cartilage or bone
4. circulatory system modified –> have a closed system with a heart that has 2 chambers… hemoglobin is present in blood cells and blood is oxygenated through gills or lungs
5. Pharyngeal slits –> gill slits in aquatic species and parts of ear in terrestrial species

Question 5

What did the transition fossil from china show?

Answer 5

it showed apparent morphological gradation between on-craniate and craniate chordates
- it showed a haikouella that had eyes and a brain but no brain case and a haikouichthys that had a braincase

Question 6

Which two extant classes of craniates lack jaws? what features do they have instead?

Answer 6

• the myxini and the petromyzontida

- they also lack teeth and paired limbs with long tubular flexible bodies and no appendages

Question 7

What are some features of the Class Myxini and which species does it include?

Answer 7

• includes hagfish
• they lack vertebrae (only living craniate that does) but has a notochord
• it has a cartilaginous cranium and other skeletal elements
• mouth is surrounded by tentacles

Question 8

How do hagfish feed?

Answer 8

• they feed on soft bodied worms or corpses of larger animals
• they grip the flesh using their keratinous plates and tie their body in a knot and then slide the knot forwards until its braced against the fresh and then pull off a chunk

Question 9

How do myxini like hagfish protect themselves?

Answer 9

they let out slime and the slime absorbs water and swells up and it usually chokes the predators