Chordates

Question 1

Summary

5 key features of the Chordates

Answer 1

1. Notochord,
2. dorsal hollow nerve cord,
3. pharyngeal slits,
4. endostyle,
5. post anal tail

Question 2

Chordates are Deuterostomes [all previous to this protostomes]
4 points

Answer 2

1. Triploblastic
2. Radial cleavage
3. Mesoderm comes from archenteron (=enterocoely)
4. Blastopore becomes anus

Question 3

classification

Answer 3

Phylum: chordates

Question 4

Definition of chordates

Answer 4

1. Deuterostomes that have, for at least part of their life cycle:

A notochord (L. chorda = “string”)

A hollow dorsal nerve cord

Pharyngeal slits

An endostyle

A post-anal tail

Question 5

Notochord [important in function]

6 points

Answer 5

1. A flexible rod of glycoproteins encased in actin
2. Mesoderm origin
3. Muscle attachment
4. Precursor of vertebrae
   In most vertebrates it becomes part of the intervertebral disc
5. Signalling during development
6. Can be found in:
   Cephalochordates, larvae of tunicates

Hagfish, lampreys

African lungfish, coelocanth, sturgeons, tadpoles

Question 6

Hollow Dorsal Nerve Cord

Answer 6

1. Forms from the ectoderm

2. In non-chordates, the nerve cord is solid and ventral

Question 7

Pharyngeal Slits

Answer 7

1. Openings in pharynx
   Allow water to flow in via the mouth and out of the pharynx
   Filter feeding

Retained as gill slits in jawless fish (7) 
cartilaginous fish (5, occasionally 6-7)  
bony fish (1)

2. Pharyngeal arches become, in vertebrates:
Jaw bone(s)

Hyoid bone

In fish: brachial skeleton (supports gills) and/or pharyngeal jaws

In tetrapods: parts of ear, tonsils, thymus

Question 8

Endostyle

3 points

Answer 8

1. Organ within the pharynx
   Present in cephalochordates, tunicates, larval lampreys; assists in filter feeding
2. Secretes mucus
   Food particles adhere to mucus
   Cilia sweep mucus through pharynx into oesophagus
3. Adapted into thyroid gland

Question 9

Post-anal tail

4 points

Answer 9

1. Has muscular (and skeletal) components
2. Notochord and nerve cord extend into the tail
3. Evolved for propulsion in water
4. In non-chordates the digestive system runs the full length of the body.

Question 10

Respiration & Circulation

2 points

Answer 10

1. The primitive chordate respires through diffusion across skin

Pharyngeal slits devoted to feeding not oxygen exchange

2. Basic circulation of blood

Dorsal system of vessels run from head to tail, paired aortae in front half

Ventral vessels run from tail to head via the liver

Question 11

Nervous system

Answer 11

1. Dorsal nerve cord protected by the notochord
2. Slight enlargement at anterior end forms brain
3. Visual sense organs located in neural tube
   Frontal eye
   Joseph cells in dorsal part
   Hesse organs in ventral part
4. Oral cirri have sensory cells

Question 12

Digestion and Excretion

4 points

Answer 12

1. Gather plankton into pharynx
2. Attaches to mucus produced by endostyle

Cilia push mucus over pharyngeal arches

Once laden with food, mucus pushed into digestive tract

3. Water passes through pharyngeal slits into atrium and then out via the atriopore / gonopore
4. The liver is a blind-ending caecum that branches from the gut

Cell lining engulfs food particules

Question 13

Other Systems
Excretion
4 points

Answer 13

1. Segmented ‘kidneys’ have protonephridia
2. More like the invertebrate system
3. Blind-ended
4. Osmoregulation through partial pressurisation

Question 14

Other Systems
Reproduction
4 points

Answer 14

1. Segmented gonads
2. Spawn once a year
3. External fertilisation
4. Larvae are planktonic

Question 15

Phylum Chordata

3 points

Answer 15

1. May be a very old phylum (c. 505 Mya) during the Cambrian explosion
2. Subphylum: Cephalochordata
3. Olfactores
   Subphylum Tunicata
   Subphylum Vertebrata

Question 16

Cephalochordata (subphylum)

3 points

Answer 16

1. Notochord extends into head
2. Lancelet or amphioxus (AGr amphi = “on both sides” + oxus = “pointed, sharp”)
3. Spend most of time half-buried in sand, filter feeding

Question 17

Tunicata
(subphylum)
5 points

Answer 17

1. Well-developed heart and circulatory system
2. Carries oxygen and nutrients dissolved in plasma
3. Hollow cerebral ganglion and neural gland
4. Produce cellulose for various functions
5. Suspension feeders, employing endostyle and pharynx

Question 18

Vertebrata

subphylum

Answer 18

1. L. vertebra = “(spine) joint”
2. Also called “Craniata” (L. cranium = “skull”)
3. Hagfish do not have vertebrae

Question 19

Agnatha

3 points

Answer 19

1. Formerly, the living members were put into two classes:

Myxini (hagfishes)

Hyperoartia (lampreys)

2. Now recognised as single monophyletic group called Cyclostomata
3. Well-represented in fossil record by other classes such as conodonts and ostracoderms

Question 20

Agnatha
Bodyplan
4 points

Answer 20

1. No jaws
2. No paired fins or other limbs (in modern forms)
3. Notochord in both larvae and adults
4. Seven or more paired gill pouches

Question 21

Agnatha

Respiration

Answer 21

1. Water taken and out of pharynx through gill pores

Question 22

Agnatha
Circulation
4 points

Answer 22

1. Two-chambered heart
   Only has deoxygenated blood
2. Aorta branches into two to serve gills
3. Accessory pumps
4. Blood returns to heart via veins

Question 23

Agnatha
Digestion
4 points

Answer 23

1. No definable stomach
2. Pharynx subdivided by valve
3. Prevents food entering the respiratory system
4. Can eat and breathe at same time

Question 24

Agnatha
excretion
4 points

Answer 24

1. Paired kidneys
2. Two ureters open into urogenital sinus
3. Maintain osmotic neutrality with environment
4. Regulation of ions rather than water

Question 25

Agnatha Nervous system 4 points

Answer 25

1. Brain and nerve cord 2. 10 pairs of cranial nerves 3. Spinal nerves 4. Autonomic nervous system

Question 26

Agnatha senses 6 points

Answer 26

1. Olfactory sac Single nostril, does not connect to respiratory system 2. Eyes 3. Pineal apparatus (‘eye’) [3rd eye] 4. Integumentary photoreceptors 5. Ears 6. Lateral line

Question 27

Agnatha Reproduction 5 points

Answer 27

1. External fertilisation 2. Believed to only breed once in their lives 3. Most species of hagfish are hermaphrodites 4. Larvae of lampreys = ammocoetes Filter feeders Closely resemble cephalochordates in this form Undergo metamorphosis 5. Hagfish don’t have larval stage

Question 28

Agnatha | Ecology : Lampreys

Answer 28

1. Coastal / freshwater 2. Many species migrate to freshwater to mate 3. Feed on live prey Mostly blood, inject anticoagulants

Question 29

Agnatha Ecology : Hagfish 4 points

Answer 29

1. Marine 2. Mostly scavengers 3. Tie themselves into knots to lever scraps of food off carcasses 4. Can produce copious amounts of slime Expands in water – one hagfish can produce 20 litres

Question 30

Tunicata Ascidiacea (Sea squirts) 4 points

Answer 30

1. Sessile, solitary or colonial 2. Filter feeders Water enters through oral siphon, through pharynx, and out through cloacal siphon 3. No excretory or respiratory organs 4. Tunic Secreted by epithelial cells Often pigmented

Question 31

Tunicata Appendicularia (salps) [barrel shaped planktonic tunicate] 6 points

Answer 31

1. Common planktonic organisms, mostly transparent 2. U-shaped body with trunk and elongated tail 3. Trunk has all organs and a midventral anus 4. Tail contains notochord, nerve cord, and 2 muscle bands 5. Protoandrous (“male-first”) hermaphrodites 6. House Secreted by epithelial glands Simple temporary structures or more complex in form