Gnathostomata Flashcards
Give the 3 top level groupings contained within this super class.
Placodermi
Chondrichthyes
Teleostomi
Which species within this group are extinct in the modern day ?
Placodermi
Give the basic features of the Placodermi.
Dorso-ventrally flattened
Armoured skin, mineralised so very heavy
Benthic feeder.
Give the 2 classes found within the extant Chondrichthyes
Holocephali
Elasmobranchi
Give the main species found within the holocephali.
Chimaeriformes, Ratfishes
Describe an adaption of the ratfishes scales
They are placoid, homologous to vertebrate teeth.
Have a layer of dentine and enamel.
Give the characteristics of Elasmobranches.
5 to 7 gill clefts
Rigid dorsal fins
Small placoid scales
Give examples of species found in this class.
Rays, Sharks, Sawfish
Describe what would happen if there was no osmoregulation in elasmobranchs.
Salt water has a higher molarity than blood. If left unchecked water would diffuse out and ions flow in.
How is water retained within the elasmobranch ?
Utilise ion pumps in gills and rectal gland to excrete excess ions
Concentrate Urea
Describe the osmoregulation of a sawfish
Derived ray, freshwater habitat.
Therefore has low blood ion concentrations and low urea to excrete as much water as possible.
Describe some of the elasmobranchs sensory adaptions.
Vision- Tapetum (reflective tissue in eyes) Hearing Lateral line Notice chemical changes Passive electroreception
Describe the process of detection via Lateral line
Line of pores on outside of the fish
Vibrations in the water enter line and shake cupula.
This gives the fish sensory awareness.
What is passive electroreception ?
The elasmobranch cannot generate electric fields but can detect those generate by other animals.
this enables detection in the dark.
Give the 3 forms of elasmobranch reproduction
Oviparity
Viviparity
Ovoviviparity
Nearly all skates and some sharks reproduce via…
Oviparity
The eggs are laid and develop outside the female
(mermaids purse)
All rays and some sharks reproduce via…
Viviparity
Internal brooding, A yolk sac placenta is present which enables transfer of nutrients
Most sharks reproduce via…
Internal brooding, No transfer of nutrients (yolk only)
Describe the cannibalism that can occur between shark embryos.
In some sharks, embryos will eat other eggs lain as a form of nutrition.
Describe the process of serial tooth eruption in sharks
Have several rows of continually growing teeth.
The new teeth will form inside the jaw, tilting forward when ready to appear in the jaw line.
What is the advantage of serial tooth eruption ?
Enables the tooth to grow faster and in the protection of the jaw
Sharks have a spiral intestine, why is this advantageous ?
Enables rapid absorption and re-absorption of food. increasing efficiency.
Give the means of respiration in a shark.
5 gills
Spiracle
What problems do sharks face when generating buoyancy ?
They live in marine environments
sea water is more dense than freshwater so requires greater generation of lift
