Animal Diversity lecture 18 Agnathans Flashcards

1
Q

Agnathans

A

Jawless fish

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2
Q

What are the extinct Agnathans

A

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
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3
Q

What are the present day Agnathans

A
  • cyclostomes

- extant = lampreys + hagfish (very closely related)

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4
Q

how does haemoglobin show us the link between lampreys and hagfish

A
  • 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
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5
Q

Lamprey features

A

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)

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6
Q

Describe lamprey reproduction.

A

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.
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7
Q

How do larval lamprey differ from adults

A
  • use gills for filter feeding, spend 5-6 years in larval stage (more time than as an adult)
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8
Q

what happened when lampreys colonised the great lakes

A

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)
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9
Q

What types of english lampreys are there

A

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

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10
Q

Features of hagfish

A

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

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11
Q

Sensory organs of hagfish

A

1) Barbels on their head = sensory detectors

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

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12
Q

How do hagfish deal with excessive slime

A

Tie themselves into knots and push it off

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13
Q

what are jawed vertebrates called

A

-Gnathostomes, includes all extant vertebrates except hagfish+lampreys

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14
Q

what did the evolution of the jaw enable

A

Gnathostomes to feed on a wider variety of prey

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15
Q

did the evolution of the jaw cause the extinction of ostracoderms

A

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

-misconception that jawed fishes caused their extinction

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16
Q

How did the jaw evolve

A
  • Jaw evolved from anterior branchiol arch (Mandibular arch)

- branchiol archs provide support for gill slits

17
Q

What is the ventilation hypothesis for the evolution of the jaw

A
  • Arch enlargement aided ventilation , arch functional in opneing + closing entrance to pharynx
  • Vertebrates were getting larger so needed a more efficient respiring system
18
Q

Problems with ventilation hypothesis

A

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.

19
Q

function of fins

A
  • 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
20
Q

what genes control fins

A

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

  • same genes later controlled limb development in tetrapods.