Origin of Chordates

Question 1

What are the Phylum and Subphylum of the Chordates?

Answer 1

Phylum: Chordata
Subphylum: Vertebrata

Question 2

What Phyla are close relatives of the Phylum Chordata?

Answer 2

Hemichordata (acorn worms) and Echinodermata (star fish, etc.)

Question 3

What group contains all three Chordata, Hemichordata, and Echinodermata?

Answer 3

Deuterstoma

Question 4

How many subphyla are under the Phylum Chordata and what are they?

Answer 4

There are three subphyla

1. Urochordata
2. Cephalochordata
3. Vertebrata

Question 5

Briefly explain defining characteristics of the Phylum Hemichordata

Answer 5

• burrowing marine worms
• use proboscis for locomotion and feeding
• shares pharyngeal slits with chordates

Question 6

Briefly explain defining characteristics of the Phylum Echinodermata

Answer 6

• marine deuterostomes
• radial symmetry as adults
• bilateral symmetry as larvae

Question 7

Briefly explain defining characteristics of the Subphylum Cephalochordata

Answer 7

• aquatic filter feeders
• pharyngeal gill system driven by cilia
• no differentiated brain, special sense organs, or heart

Question 8

Briefly explain defining characteristics of the Subphylum Urochordata
BONUS: give an example

Answer 8

• marine filter feeders
• live in varied encasements -> tunics

BONUS EXAMPLE: Ascidiacea (sea squirts, ascidians)

• swimming larva, sessile adults
• larvae have more chordate characters than adults do

Question 9

What are the 5 characters seen in all chordates?

Answer 9

1. Notochord
2. Dorsal hollow nerve cord
3. Pharyngeal slits/pouches
4. Postanal tail
5. Endostyle or thyroid gland
   * *all five MUST be present at some stage in life

Question 10

Explain the structure and function of the notochord

Answer 10

Structure: fluid-filled elastic rod, dorsal to gut tube, ventral to nerve cord, often disappears/becomes highly modified
Function: keeps body straight, prevents muscle collapse during muscle contraction, organizes embryological development of nearby structures

Question 11

Explain the structure of the dorsal hollow nerve cord

Answer 11

• hollow tube formed by invagination of surface cells in embryo
• neural tube dorsal to gut tube

Question 12

Explain the structure and function of the pharyngeal slits

Answer 12

Structure: found in pharyngeal area of digestive tract behind oral cavity, slits in wall of pouches
Function: differs between aquatic and terrestrial species; creates water current between mouth and pharynx for feeding/respiration in aquatic species. In terrestrial species they are transient embryo structures

Question 13

Explain the structure and function of the postanal tail

Answer 13

Structure: posterior to anus (like it sounds)
Function: swimming

Question 14

Explain the structure and function of the endostyle

Answer 14

Structure: Glandular groove on the floor of pharynx
Function: secretes mucous, traps food particles, involved in iodine metabolism