Chordates

Question 1

Chordates have particular features

Answer 1

1. Notochord - either all or some of their lives - sandwiched between gut and NS
   - ‘flexible rod’ providing support
2. Dorsal, hollow nerve cord - others have ventrally placed
   - unique and can develop into NS and brain
3. Pharyngeal (gill) slits - in pharynx of ut
   - used for feeding initially but evolve into repsiration
4. Post anal tail

Question 2

2 groups of invertebrate phyla

Answer 2

1. Urochordates (tunicates)

2. Cephalochordates (lancelets - Amphioxus)

Question 3

Urochordata morphology of larva and adult and feeding

Answer 3

• Tadpole-like larva - all characteristics of chordates
• Undergo metamorphosis into adult, lose majors of features except gill slits
• NS reduced in adult
• Pharynx is enlarged and covered in pharyngeal slits in feeding
• Animal draws water in incurrent (buccal) siphon passing over slits that produce mucous and leave excurrent (atrial) siphon

Question 4

Metamorphosis of Urochordata

Answer 4

1. Larval stage swims around and will settle on its head
2. It adheres to surface
3. Differential growth occurs pushes the siphons around
4. Buccal siphon goes from being near the substrate (where it becomes adhered to the surface on its head) to opposite end of the animal (away from substrate)
5. Atrial siphon moves from being above buccal (near anus) to opposite side of buccal siphon nearer top of animal (away from substrate)
6. Notochord becomes less rigid, loses turgor and is absorbed - and tail
7. NS becomes reduced

Question 5

Cephalochordata features

Answer 5

Amphioxus and lancelets
•filter feeders - using pharyngeal slits for feeding
•all of chordate features
•notochord extends whole of animal to anus and into head
•slight swelling of notochord = brain
•mucous produced in and across gill slits by endostyle
•gill slits open into atrium that surrounds body - so many would make body wall weak if opened directly out of animal

Question 6

Differences between inverts and chordates

Answer 6

Chordates are dorsoventrally inverted
•opposite way to what is seen in inverts - their dorsal is the inverts ventral
•suggested animals started swimming on backs - as everything is the opposite
•molecular techniques demonstrate this clearly
-genes and proteins are expressed ventrally in non-chordates and dorsally for a chordate, those expressed dorsally in non-chordates are expressed ventrally in chordates

Question 7

Phylogeny of chordate group

Answer 7

Closest related to vertebrata thought to be cephalos (even though their more mobile and look similar), but actually uros
•based on molecular techniques and morphological info
•uros have similarities in development and genetics
•urochordates are considered to be highly specialised - adopting a new lifestyle in their evolution