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Animal Diversity > Chondrichthes > Flashcards

Chondrichthes Flashcards

1
Q

Spiny sharks

A 
Acanthodians
•spines of body
•variable but not very large
•some were toothless - others found to have a tooth whorl
•basal cartilaginous fish?
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2
Q

Chondrichthyes features

A
  • first appeared over 400mya
  • characterised by having a mineralised cartilaginous skeleton (advantageous as they are heavy-bodied and makes them very manoeuvrable)
  • lipid-filled liver
  • high blood urea concentration
  • most have hyostylic jaw suspension
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3
Q

Lipid-filled liver…

A

•it can take up to 25% of their body weight
•contains lipids to lighten body for buoyancy
•varies in size dependent on whether the animal is benthic (don’t need to be as buoyant = smaller), or open ocean dwelling (bigger)
-lipids inside contribute to this too

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4
Q

High blood urea concentration

A

•can harbour particular chemicals in their tissues and blood - like urea to push osmotic potential of blood higher
•either isosmotic (same conc as seawater) or hyperosmotic (more conc than seawater)
-makes less dense and more buoyant

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5
Q

Hyostylic jaw suspension…

A
  • amphystylic condition is the ancestral form - some attachment and support from 2nd gill arch
  • upper jaw becomes almost detached from the skull (some through hyomandibular arch) - only attached via ligaments
  • allows movement of upper jaw - to protrude it, moving independently of cranium
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6
Q

2 sub groups of Chondrichthyes

A
  1. Holocephalii - e.g. rat fish, found at lower depths

2. Elasmobranchs - sharks, rays and skates

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7
Q

Holocephalii morphology

A

•proboscis ‘type-thing’
•whip-like tail
•well developed pectoral fins
•few gill arch
•has rostrum
•holostylic jaw suspension - upper jaw fused with cranium
-feed on crustaceans and molluscs so is a hard grinding surface
•dorsal spines produce toxin - defence again predators

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8
Q

Holocephalii sensory structures

A
  • head rich in mechanoreceptors

* electroreceptors pick up electrical discharge of prey

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9
Q

Holocephalii reproduction

A

•head has clasper in Ms used for reproduction
-latch onto females neck where corresponding hole is found
-holds in place whilst mating
•they lay eggs

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10
Q

Elasmobranch groups

A
  1. Galeomorphs - larger and active, predacious forms (usually), associated with warmer water (not exclusively)
    - many are apex predators
    - has an anal fin
  2. Squalomorphs - live in cooler, deeper water and tend to be smaller
    - no anal fin
  3. Batoidea - skates and rays
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11
Q

Batoidea

A
  • dorsoventrally flattened shape - associated with a benthic lifestyle
  • mouth and gill underneath
  • spiracle draws water in through animal and leaves via gills
  • incredibly protrusive mouth and crushing teeth which allow them to feed on molluscs & crustaceans on sea floor
  • more variable than the sharks
  • enlarged pectoral fins used for swimming and can bury themselves
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12
Q

Differences between skates and rays

A

Skates…
•have smaller dorsal fins on tail
•lay eggs
•produce low electrical current from tail for communication
Rays…
•have barb on their tail - modified denticle used in defence
•rays can give birth to live young
•produces more powerful currents using muscles in their gills for prey capture (200V)

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13
Q

More cartilaginous fish characteristics …

A

•short intenstine (most carnivorous) with a spiral valve to increase SA
•heterocercal tail (asymmetric), top is longer - gives trust and life
•placode scales - denticles in sharks
•skates have denticles across midline - enlarged
•stingrays have it modified into a poisonous barb
•tooth whorl - lack dermal bone in jaw, teeth form in skin that rests on jaw
-teeth can be replaced if they get damaged
•teeth designed for max damage - but vary in structure dependent on spp

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14
Q

Sensory system of Chondrichthyes

A
  1. Mechanoreceptors - neuromast organs and the lateral line - detect vibrations and water displacement
  2. Chemoreceptors - acute sense of smell
  3. Electrical impulses - Ampullae of Lorenzini or ampullarf organs
  4. Well-developed vision for low-light (sharks)
  5. Large brains
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15
Q

Chemoreceptors of Chondrichthyes

A

2 nostrils linked to olfactory tracts and bulbs
•some olfactory bulbs in sharks can be very large (1 part per billion), detecting blood and body fluids
•turn to side stimulated first wherever the cue came from - maximises likelihood of encountering prey

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16
Q

Electrical impulses

A

Ampullae of Lorenzini
•found exclusively on the head of sharks
•found on pectoral fins of skates and ray
•detecting nervous communication and electrical impulses sent between the nerves of muscles etc. in prey
•work has been done to demonstrate this - where sharks go for prey if electrodes are in the water - with no scent cues

17
Q

Vision of sharks

A

For deeper water or hunting at night
•rod cell rich retina
•cells with crystals of guanine (tapetum lucidum) - forms a mirror-like structure behind retina
-light enters the eye and reflects back onto the retina, can pick up any light levels
- may dazzle prey when sun shining behind the prey?

18
Q

Sequence to their systems - predation

A
  1. Olfaction (especially when prey wounded) or mechanoreception first (lateral line)
  2. When close enough will use vision for detection - see if they recognise it
    - will knock prey if don’t recognise it, deciding if its worth eating
    - causes prey item to bleed - see if they know the smell
  3. Attack - close eyes via eyelid (nictitating membrane) for protection, and use electroreception to guide them
    - great white kills via exsanguination (bleeds to death) for protection
19
Q

Chondrichthyes reproduction

A
  • reproduce later in life
  • internal fertilisation
  • M pelvic fin modified into clasper - passes sperm to female reproductive opening (cloaca)
  • claspers can be modified to have barbs and hooks to lock into place
  • M shark wrap selves around F and bite to keep in place (F has thickened skin)
  • Skates and rays dentition changes for reproduction - more pointy in reproductive period to hang onto female
20
Q

Chondrichthyes egg laying

A
  • mermaids purses or egg cases can have tendrils to attach to rock or seaweed
  • some shaped like screws to bury into rocks
  • impermeable but have holes where water can get in - allows gaseous exchange
21
Q

Chondrichthyes ovoviviparity

A

Retains eggs inside F reproductive tract
•all nutrition comes from egg, not F
•eggs hatch ad F gives birth to live young

22
Q

Chondrichthyes viviparity

A

Nutrition from female, as well as yolk = matrotrophy
•F secretes fluids to tract to feed young
•some continue to ovulate to feed young
•some young feed on siblings…
•some the yolk sac itself is highly vascularised and becomes like a placenta - movement of blood between mother and embryo (lemon shark) - placentotrophic viviparity
•retain young for long period of time - no parental care though

Animal Diversity (42 decks)

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