Chondrichthyes Flashcards
What are the 5 features that unite chordates?
>notochord >postanal tail >z-shaped muscle segments >pharyngeal slits >dorsal hollow nerve chord
What are the features that unite vertebrates?
What about gnathostomes?
>vertebrae >eye >cranium >brain >tongue >gill arches
> mineralised teeth
1st gill arch forms jaws
paired fins
Why is a shark’s life cycle unusual?
Lay few large eggs w/ big yolks
–>Intensive parental investment
Some sharks e.g. hammerhead:
eggs are retained & hatch internally - fed via placenta or other eggs
How do sharks mate?
Have claspers - extensions of pelvic fins
Males fertilise eggs inside the female
= higher chance of fertilisation –> less risk to having just a few offspring
What are shark claspers convergent to?
The intromittant organ of amniotes
Describe the hydrodynamics of sharks
Large, oily liver helps them float
- but denser than water so must swim to stay up in water column
Don’t have a swim bladder
How do sharks breathe?
Ram-breathers
= ventilate gills by forcing water through open mouth
If stop swimming = drown & suffocate
Describe a shark’s skeleton
Reduced & cartilaginous
= low density
Lack bone internally
- never evolved bone vertebrae
External bony plates of skull, jaws & body lost - reduced to denticles
= made of enamel + dentine
How do sharks reduce drag?
Denticles have parallel giblets
- control production of vortices along body
= reduces drag by 10%
How are sharks specialised for high speeds?
Teardrop body
Lunate tail
Elongated fins
Why do sharks replace their teeth every 9-36 days?
Fish bones & scales rapidly dull teeth
How are shark jaws highly flexible?
What is so special about Goblin sharks?
Jaw cartilage isn’t tightly connected to skull bones
Can protrude jaw to seize prey
What is eyeshine?
What is its importance?
When photons pass through retina w/out activating photoreceptors & bounce back
Increases sensitivity of retina to light
What is are the ampullae of lorenzini?
Electroreceptors
- detect electric fields
Can home in on prey under seafloor w/out replying on light
How do sharks smell?
Each nostril has an incorrect & excurrent opening
Water passes over folds of chemosensitive olfactory tissue
How are sharks specialised for hunting?
> specialised jaws & teeth
can hunt in low light conditions
- smell & electrical signals
What are the 3 main cnrondrichthyes groups?
Holocephali = Chimeras Selachimoprha = Sharks Rays = Batoidea
Give an example of a Holocephali (Chimera)
Describe them
Ratfish (aka rabbitfish)
> Toothplates
- incisor like structures to crush prey
Big eyes for darkness
Swim w/ winglike pectoral fins
Which era are Chimeras from?
Carboniferous
What are the features of Batoidea?
> flattened body
-glide over seafloor
large pectoral fins extend onto head
pavement of small teeth to crush invertebrates
Give examples of Batoidea
Sawfish Torpedos Skates Stingray Manta
What are the features of sawfish?
Long nose w/ spines
= modified denticles
(- NOT teeth)
to club & stun/kill fish
What are the features of torpedos?
Modified muscle cells discharge an electric pulse
- stuns predator/prey
What are the features of skates?
Instead of swimming they walk using finger-like projections of pelvic fins
