L14 Hemichordates and chordates

Question 1

What are the general chordate features?

Answer 1

Have a notochord
Dorsal hollow ventral nerve chord
Pharyngeal gill slits
Endostyle
Post anal tail

Question 2

What is a notochord?

Answer 2

Longitudinal flexible rod located between digestive tract and nerve cord in embryo - not always in adults

Question 3

What is a dorsal hollow ventral nerve chord?

Answer 3

Forms from a rolled up plate of dorsal ectoderm, part is thickened and forms the brain

Question 4

What are pharyngeal gill slits?

Answer 4

Slits in the pharyngeal region of the digestive tract that allow water to pass through, primitively used for feeding. Lost in adult humans

Question 5

What is an endostyle

Answer 5

Ciliated groove on pharynx which produces mucus to gather food particles. Acts as a thyroid gland, concentrating iodine in water/blood

Question 6

What is different about the hemichordates?

Answer 6

Don’t have all these features

Question 7

What species make up the hemichordates?

Answer 7

Less than 100 species, 70 are the enteropneusts (acorn worms) and 20 are the Pterobranchs (sea angels)

Question 8

What are the general features of the enteropneusts?

Answer 8

3 body regions
Have gill slits for respiration
Deposit feeders of sand/mud
lives in burrows
In larval stage, look like echinoderm 
Have nerve net 
Proboscis for food collection

Question 9

What are the general features of the enteropneusts?

Answer 9

Only a few mm long
Sessile, colonial 
Some have gill slits 
Traced back to the graptolites 
Lophophore feeding device

Question 10

What are the graptolites?

Answer 10

Around in the Cambrian - Devonian, ancient forms of sea angels.

Question 11

What resemblance do the hemichordates have to the chordates?

Answer 11

Stomochord is similar 
No tail
Nervous tissue can be hollow, but no dorsal cord
Collect food externally
Have gill slits

Question 12

What resemblance do the hemichordates have to the echinoderms?

Answer 12

Similar larval stage
Similar nervous system - nerve net
Gill slits - may have been present in ancestral echinoderms

Question 13

What are the two invertebrate phyla of the chordates?

Answer 13

Urochordates (tunicates), Cephalochordates (lancelets)

Question 14

What are species in the urochordates?

Answer 14

Tunicates

Question 15

What are the general features of the urochordates?

Answer 15

Adult is sessile
Water goes into incurrent siphon, out of excurrent
Has pharynx with numerous slits
Adult has no tail, dorsal hollow/notochord
Larvae have chordate features - lost in metamorphosis
Many colonial
deep sea may be modified to trap food

Question 16

Describe tunicate developement from the larval stage

Answer 16

Larval stage settle son head, tail and notochord are reabsorbed, growth pushes animal round, two siphons grow - buccal and atrial

Question 17

What are the species in the cephalochordates?

Answer 17

lancelets, amphioxus

Question 18

What are the general features of the cephalochordates?

Answer 18

Retain chordate features as adults
Notochord goes into head rejoin forming a primitive brain
Filter feeders