The chordates

Question 1

What 3 main groups does chordata contain?

Answer 1

1. Craniates
2. Cephalochordates
3. Urochordates

Question 2

Of the 3 main chordate groups, which 2 are most closely related?

Answer 2

Craniata and urochordata.

Question 3

What are 4 major synapomorphies of the chordates?

Answer 3

1. Notochord
2. Dorsal hollow nerve chord
3. Myotomes
4. Pharynx and pharangeal openings

Question 4

What is the neural tube?

Answer 4

A structure homologous to the vertebrate spine, it does not expand at the end into a brain.

Question 5

What is the notochord?

Answer 5

A stiffened rod of tissue that provides points for muscle attachment in locomotion. Homologous to the vertebral column.

Question 6

What is a common example of a cephalochordate?

Answer 6

Amphioxus.

Question 7

Give an example of a urochordate?

Answer 7

Sea squirts (tunicates).

Question 8

What is Pikaia?

Answer 8

A fish-like organism from the Middle-Cambrian.

Question 9

Why is Pikaia assumed to be the earliest known chordate?

Answer 9

It had a notochord and myotomes.

Question 10

Why are the conodonts thought to be a sistergroup to the vertebrates?

Answer 10

They have bilateral symmetry, an enlarged brain and eyes.

Question 11

From which group did the vertebrates evolve?

Answer 11

Craniata.

Question 12

What are the 2 major groups of extinct agnathostomes?

Answer 12

1. Cephalaspidomorphs

2. Pteraspidomorphs

Question 13

What are the 2 major groups of extant agnathostomes?

Answer 13

1. Hagfish

2. Lampreys

Question 14

What are the 2 major divisions in the cephalaspidomorphs?

Answer 14

1. Anaspids

2. Cephalaspids

Question 15

What kind of tail did anaspids have?

Answer 15

Hypocercal tails.

Question 16

What kind of tail did cephalaspids have?

Answer 16

Heterocercal tails.

Question 17

What is a hypocercal tail?

Answer 17

The tail is weighted/stiffened at the bottom and flexible at the top. This pushes water backwards and up in locomotion, creating lift at the front of the animal.

Question 18

What is a heterocercal tail?

Answer 18

The tail is weighted/stiffened at the top and the bottom is flexible. This pushes water backwards and down during locomotion, creating a downward movement. This is counteracted by pectoral fins that create lift at the front of the animal.

Question 19

What 5 features are characteristic of cephalaspids?

Answer 19

1. Dorsoventrally flattened
2. Large head-shields
3. Polygonal scales for electrical detection
4. Evidence of a lateral line system
5. Fleshy pectoral fins to counteract the heterocercal tail

Question 20

What are 4 major characteristics of pteraspidomorphs?

Answer 20

1. Heavy head armour and chainmail scales at the posterior for flexibility
2. Hypocercal tail to counteract weight from heavy head armour
3. No paired fins, presence of spines instead
4. A single, posterior opening for all gill slits

Question 21

How many species of hagfish are there and what kind of lifestyle do they have?

Answer 21

2, scavenging.

Question 22

How many species of lamprey are there and what kind of lifestyle do they have?

Answer 22

7, parasitic.

Question 23

What 5 synapomorphies do hagfish and lampreys have?

Answer 23

1. No jaws
2. No caudal fin
3. Elongate bodies
4. No appendages
5. No true vertebrae (notochord instead)

Question 24

Which group are the extant agnathostomes thought to be descended from?

Answer 24

Anaspids.

Question 25

What are 3 major synapomorphies of vertebrates?

Answer 25

1. A centralised nervous system whereby the spinal chord has enlarged at one end to form the brain.
2. 3 paired sensory organs in the head; optic, olfactory and otic capsules
3. Development of the vertebrae to form the backbone.

Question 26

The neural tube and notochord in chordates are homologous to which structures in vertebrates?

Answer 26

The spinal chord and backbone respectively.

Question 27

From which period of geological time do we begin to see well-preserved vertebrate specimens?

Answer 27

The Ordovician.

Question 28

How do agnathostome gills work?

Answer 28

By tidal flow.