Chondrichthyes Flashcards
What are some features of the gnathostomes?
Jaws with teeth
Paired fins
Neck
Improved locomotion
Improved predatory abilities
Sensory system
Circulatory system
What are the four main groups of gnathostomes?
Acanthodians
Chondrichthyans
Placoderms
Osteichthyans
Give some features of the placoderms
Extinct - most went extinct during the Devonian period (430-360 MYA)
Had bony shields/plates
Had a variety of body forms and sizes (some up to 8m)
Could live in freshwater or marine water
Had teeth but these could not be replaced
Had viviparity
Had claspers (only found on males) - used to transfer sperm for internal fertilisation. These are NOT homologous to those in cartilaginous fish
Give some features of the acanthodians
Extinct
Basal chondrichthyans - so known as the spiny sharks
Could live in marine water or freshwater
Between 20cm - 2m in size
Were either toothless or had a tooth whorl
Give some features of the chondrichthyes
First appeared 400 MYA
Cartilaginous skeleton that is mineralised to make them lighter
Have a lipid filled liver which increases buoyancy (can be 20% of body weight) - more fats increases liver size
High blood urea concentration
Most have hyostylic jaw suspension - upper jaw is attached to skull by hyomandibular and ligaments increase the flexibility of the jaw
Internal fertilisation - males have claspers
Are chondrichthyes jaw independent or dependent from the cranium?
Independent
Means can drop upper jaw from the cranium
Skates and rays can fully drop jaw to substrate for feeding
What are the two groups of chondrichthyes?
Holocephalans - e.g. chimaera
Elasmobranchs - sharks, skates, rays
Sharks can be further classifed into galeomorphs (if they have an anal fin) or squalomorphs (no anal fin) - DONT NEED TO KNOW THIS
Skates and rays can be further classifed into batoidea
Give some features of the Holocephalans
Holostylic jaw which is fused with skull - they eat hard-bodied animals so this allows them to crush prey (also have tooth plates for crushing)
Live in depths of 500m
Have a tail
Have four gill openings
No spiracle
Large pectroal fins
Oviparous (possibly viviparous in the past)
Have a proboscis that contain mechano and electroreceptors
Spine which can be venomous
What are some reasons for the hammerhead sharks looks?
Improve sensitivity of the receptors
Enhanced binocular vision - increased eye distance causes an increased field of view overlap (helps with accurate perception of depth and distance)
Give some features of the batoidea
Dorso-ventrally compressed
Spiracle to draw water in
Mouth and gill slits
Enlarged pectoral fins
Many are benthic
Jaw protrusible
Cephalic find for filtering water into mouth to trap any food
Teeth are flat plates and can be sexual dimorphic - male uses teeth to grab onto female whilst mating (can also change teeth depending on season as need different teeth for feeding and mating for males)
Some can produce electric currents for either stunning prey or communication
Give some features of sharks
Have paired fins
Liver can be 25% of body mass - to help buoyancy
Have a mouth, spiracle, gill pouches and a heart
Have a short intestine but have a spiral valve which increases surface area of intestine
Have a heterocercal tail with vertebrae in the upper lobe
Have placoid scales which are species specific and help reduce turbulence
Describe the placoid scales in skates and rays
Rays - scales cover just the barb
Skates - cover the whole tail
Are batoidea vivparous or oviparous?
Rays are viviparous
Skates are oviparous
Describe the teeth whorl
Teeth form within the skin and the tooth whorl rests on the jaw
The teeth are NOT embedded into the jaw
Teeth can be continually replaced
Teeth shapes can vary to maximise damage
What are the different ways chondrichthyes can feed?
Suction feeding
Filter feeding
Biting
Predatory sharks often kill mammal prey via exsanguination
Give some ways that sharks are effective predators
Have a lateral line system, which detects wake of swimming fish or vibrations of struggling fish
Have mechanoreceptors - use vibrations (via neuromast organs)
Have chemoreceptors - many have an acute sense of smell but this depends on the size of the olfactory bulb (sharks in deeper water have larger olfactory bulbs as cant rely on vision)
Nostrils work almost independently, whichever nostril detects a stimulus first, the shark will turn to side first and move towards it and ignore any other stimulus that presents itself
How are electrical impulses detected?
From ampullary organs
Found:
- In the head of sharks (ampullae of lorenzini)
- Pectroal fins of rays
- Rostrum of holocephalans
In sharks they have canals filled with jelly and these can conduct electricity to signal to nerves
Give some features of shark vision
Well developed for low light intensities as they mainly feed at dawn and dusk
Have a rod rich retina
Have cells with crystals of guanine (known as tapetum lucidum) behind the retina - these can shine light back onto the retina to maximise the amount of light onto it
Give some features of cartilaginous fish brains
Proportionately heavier than brains of other fish
Similar to brain to body mass ratios for some tetrapods
Explain how sharks use their sensory systems to hunt prey
Either use olfaction (especially if prey is wounded) or mechanoreception first to detect prey
Once they get closer, use the visual system
If they do not recognise the object, they will bash into it to either sense it via touch or by making it bleed and sensing it that way
If it senses the object as prey it will attack
The nictitating membrane (like an eyelid) closes over the eye for protection and uses electroreception only to attack
Give some features of shark reproduction
They internally fertilise
Males have two claspers and during mating, one locks onto female cloaca by hooks and sperm is released through siphon sac contraction
Some males may bite females/hold onto her fins during mating - so some females have thickened skin where males are more likely to bite
What are the different ways sharks produce young?
Oviparous:
- Offspring hatch from legs
- Get nutrition from yolk
- Eggs have tendrils for attaching onto substrate
- Egg case openings and embryo movements increase water flow
Ovoviviparity
- Retain eggs into the oviduct until they hatch
-Female then gives birth to live young
Viviparity
- Birth to live young
- Get nutrition from egg yolk and the female (matrotrophy)
Give some ways viviparous chondrichthyes can get nutrition
Female secretes substances - known as uterine fluid
Some ovulate to feed young or cannibalism
Some have yolk sac placenta (known as placentotrophic viviparity)
What is the life history of a shark usually like? What are the issues with this?
Tend to reproduce later in life
Have longer life histories (e.g. greenland sharks live for 400 years and dont sexually mature until 150 years old)
Biennial - reproduce once every other year
Gestation period usually 12 months (but can range from 9-24)
Have small litter sizes (40 pups the most)
28% sharks are critically endangered (hammerheads have declined by 76-99%) which is important as they are apex predators
Atlantic cod had larger numbers, shorter life histories, could reproduce in large numbers every year (up to 11 million eggs) and they were still fishes to extinction in some areas
