sharks and rays Flashcards
what are chondrichthyes
a class of fishes that includes those with a cartilaginous skeleton.
what are the different subclasses of chondrichthyes
1) elasmobranchii- broadly divided into sharks and rays
2) Holocephali
what are batoids
Batoids are flat-bodied, and, like sharks, are cartilaginous fish, meaning they have a boneless skeleton made of a tough, elastic cartilage.
what are some charactetistics of batoids
enlarged pectoral fins fused to flattened body
gill slits on ventral surface
pair of spiracles on dorsal surface
what are the four orders of batoids
1) Rhinopristiformes (sawfishes and guitarfish)
2) myliobatiforms (sting rays)
3) rajiformes (skates)
4) torpendinformeds (electric rays)
what are the four orders of the subdivison selachii
orectoloniformes (carpet shark)
carcharhiniformes (requem shark)
squaliformes (sleeper/dogsfih sharks
squantiniformes (angel sharks)
what are the different types of fins
1) flexible, retractable and supported by soft and spiny rays in bony fishes
2) rigid and infexible, non retractable fin or present day elasmobranches
what is the difference between heterocercal tails and homocercal tails
1) hetero= different tail where upper and lower lobes are different
2) homocercal = same tail where it is externally symmertrical
how do elasmobranchs remain buoyant
they do not possess swim bladders
rely on dynamic lift to maintain position in the water
some use static lift from lipids
what is the equations for neutral bouyancy and neagtive for dynamic lift
w = submerged weight of fish
b- hydrodynamic lift from pectoral fins
c- lift from caudal fin
W= B+C = netural
W>B+C= negative and will sink
what are the disadvantages of static lift from lipids
1) lipid only slighlty less dense than water so need lots which increases bulk and therefore drag
2) quanitiy of lipids cant be adjusted qucikly so no ability to compenstate for short term changes
where do elasmobranchs store lipids
in their livers
- liver can exceed 20% of body weight
compare dynamic vs static lift
D = more economical at high speed and actively seeking prey
S = more economical at low speed so opportunistic
how many species of elasmobranchs are filter feeders
13 the rest are predatory
how do predators locate prey
usually involved a mix of visual and non-visual senses
what is the apullae of lorenzini
found in all elasmobranchs and some teleost’s
it is the sensory cells sensitive to electrical stimulus of low frequency 0.05-8Hz as well as mechanical stimulation and changes in salinity and temp
what are the reproductive strategies in most actinopteryginians
large numbers of eggs with little provision and no aftercare
what are the reproductive strategies of chondrichthyans
very few offspring with lots of provision and aftercare
all show mating with internal fertilisation
what are intromittent organs
claspers formed from the posterior portions of pelvic fins
outline elasmobranch reproudtion
oviparity = few large eggs are laid individually with large yolk reserves and tough egg cases
- development time is considerable (5-12 months)
- new born are totally independent
what is meant by unterine oophagy
consuming unfertilised eggs produced for eggs which hatched early to consume
what is uterine cannibalism
the largest foetuses consume the smaller ones until only a single pup is present in both of the uteruses
outline true viviparity in charchariniformes
the developing embryo is nourished via a placenta- the empty yolk sac attaches to uterine wall to form a yolk-sac placenta
compare chondrichythyes to osteichthyes
C = cartilginous, no bone, no operculumn, no swim bladder, ampullae or lorenzini, internal fertilization
O= bony, true bony skeleton, no spiracle, operculmn covered by gills, swim bladderm no electroreceptos, external fertilisation
