Animal Diversity lecture 18 Agnathans

Question 1

Agnathans

Answer 1

Jawless fish

Question 2

What are the extinct Agnathans

Answer 2

Ostracoderms (armoured jawless fish)

• existed 500 MYA
• one of earliest vertebrates
• vary alot in size
• fed on soft bodied animals (v small mouth)
• some had paired pectoral fins (feature similair to jawed verts) - thought to be more derived than the agnathans alive today

Question 3

What are the present day Agnathans

Answer 3

• cyclostomes

- extant = lampreys + hagfish (very closely related)

Question 4

how does haemoglobin show us the link between lampreys and hagfish

Answer 4

• 500 MYA ancestral haemoglobin split -> alpha and beta genes
• ALL vertebrates have this split, except jawless vertebrates
• Common ancestor of lampreys+hagfish predates A/B split , diverged before 500 MYA

Question 5

Lamprey features

Answer 5

1) Initially thought to be primitive, now thought they are very specialised
2) most lampreys are predaceous
3) sucker like feature = oral hood (for feeding)
4) Notochord provides support for the body as they only have minute vertebrae which flank the nerve chord -> Arcualia
5) Use tidal ventilation water is drawn over gills so they can breathe whilst feeding (they latch on)

Question 6

Describe lamprey reproduction.

Answer 6

Anadromous - spend adult life in sea and return to fresh water to breed.

• chemical cues attract the sexes
• adults die after reproduction
• adults find the streams for reproduction by following bile acids released by larval lampreys.

Question 7

How do larval lamprey differ from adults

Answer 7

• use gills for filter feeding, spend 5-6 years in larval stage (more time than as an adult)

Question 8

what happened when lampreys colonised the great lakes

Answer 8

E.g. Great lakes (1920)

• lampreys colonised great lakes, became land-locked
• complete whole lifecycle in the lakes
• problem for fish (higher predation from lampreys)

Question 9

What types of english lampreys are there

Answer 9

1) Brook Lampreys - never becomes predaceous (does not feed as adult)
2) River Lamprey - found in coastal waters as adults (normal life cycle)
3) Sea lamprey - largest of the 3 + found in open ocean

Question 10

Features of hagfish

Answer 10

1) mainly scavengers
2) can aquire nutrients through skin and gills
3) Notochord present (rudiments of vertebrae)
4) Only verts with blood isomotic to sea
5) Glands produce slime ( alot!) as defence mechanism + potentially predatory (clog up fish gills)
6) sex ratio female biased

Question 11

Sensory organs of hagfish

Answer 11

1) Barbels on their head = sensory detectors

2) single nostril is used for smell and intake of water, flows out a single gill opening

Question 12

How do hagfish deal with excessive slime

Answer 12

Tie themselves into knots and push it off

Question 13

what are jawed vertebrates called

Answer 13

-Gnathostomes, includes all extant vertebrates except hagfish+lampreys

Question 14

what did the evolution of the jaw enable

Answer 14

Gnathostomes to feed on a wider variety of prey

Question 15

did the evolution of the jaw cause the extinction of ostracoderms

Answer 15

No , they co-existed for a long time before ostracoderms went extinct

-misconception that jawed fishes caused their extinction

Question 16

How did the jaw evolve

Answer 16

• Jaw evolved from anterior branchiol arch (Mandibular arch)

- branchiol archs provide support for gill slits

Question 17

What is the ventilation hypothesis for the evolution of the jaw

Answer 17

• Arch enlargement aided ventilation , arch functional in opneing + closing entrance to pharynx
• Vertebrates were getting larger so needed a more efficient respiring system

Question 18

Problems with ventilation hypothesis

Answer 18

1) Mandibular arch does not form fucntional gill arch in any living vertebrate
2) first arch has never been used in respiration so why would enlarging it increase ventilation (normally used in head support)
3) In agnathans gill archs are on the outside and gills on the inside. whereas in gnathostomes gill arches are on the inside.

Question 19

function of fins

Answer 19

• control how they swim and stabilise the body
• can also be used for mating e.g. brightly coloured
• can also be used for defence
• Pitch (up/down) - controlled by pelvin +pectoral fins
• Yaw (L/R) controlled by dorsal +anal fin

Question 20

what genes control fins

Answer 20

Genes responsible for dorsal fin of lamprey also responsible for midtime+ paired fins in bony fishes

• same genes later controlled limb development in tetrapods.