sharks and rays

Question 1

what are chondrichthyes

Answer 1

a class of fishes that includes those with a cartilaginous skeleton.

Question 2

what are the different subclasses of chondrichthyes

Answer 2

1) elasmobranchii- broadly divided into sharks and rays
2) Holocephali

Question 3

what are batoids

Answer 3

Batoids are flat-bodied, and, like sharks, are cartilaginous fish, meaning they have a boneless skeleton made of a tough, elastic cartilage.

Question 4

what are some charactetistics of batoids

Answer 4

enlarged pectoral fins fused to flattened body
gill slits on ventral surface
pair of spiracles on dorsal surface

Question 5

what are the four orders of batoids

Answer 5

1) Rhinopristiformes (sawfishes and guitarfish)

2) myliobatiforms (sting rays)

3) rajiformes (skates)

4) torpendinformeds (electric rays)

Question 6

what are the four orders of the subdivison selachii

Answer 6

orectoloniformes (carpet shark)
carcharhiniformes (requem shark)
squaliformes (sleeper/dogsfih sharks
squantiniformes (angel sharks)

Question 7

what are the different types of fins

Answer 7

1) flexible, retractable and supported by soft and spiny rays in bony fishes

2) rigid and infexible, non retractable fin or present day elasmobranches

Question 8

what is the difference between heterocercal tails and homocercal tails

Answer 8

1) hetero= different tail where upper and lower lobes are different

2) homocercal = same tail where it is externally symmertrical

Question 9

how do elasmobranchs remain buoyant

Answer 9

they do not possess swim bladders
rely on dynamic lift to maintain position in the water
some use static lift from lipids

Question 10

what is the equations for neutral bouyancy and neagtive for dynamic lift

Answer 10

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

Question 11

what are the disadvantages of static lift from lipids

Answer 11

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

Question 12

where do elasmobranchs store lipids

Answer 12

in their livers
- liver can exceed 20% of body weight

Question 13

compare dynamic vs static lift

Answer 13

D = more economical at high speed and actively seeking prey

S = more economical at low speed so opportunistic

Question 14

how many species of elasmobranchs are filter feeders

Answer 14

13 the rest are predatory

Question 15

how do predators locate prey

Answer 15

usually involved a mix of visual and non-visual senses

Question 16

what is the apullae of lorenzini

Answer 16

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

Question 17

what are the reproductive strategies in most actinopteryginians

Answer 17

large numbers of eggs with little provision and no aftercare

Question 18

what are the reproductive strategies of chondrichthyans

Answer 18

very few offspring with lots of provision and aftercare
all show mating with internal fertilisation

Question 19

what are intromittent organs

Answer 19

claspers formed from the posterior portions of pelvic fins

Question 20

outline elasmobranch reproudtion

Answer 20

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

Question 21

what is meant by unterine oophagy

Answer 21

consuming unfertilised eggs produced for eggs which hatched early to consume

Question 22

what is uterine cannibalism

Answer 22

the largest foetuses consume the smaller ones until only a single pup is present in both of the uteruses

Question 23

outline true viviparity in charchariniformes

Answer 23

the developing embryo is nourished via a placenta- the empty yolk sac attaches to uterine wall to form a yolk-sac placenta

Question 24

compare chondrichythyes to osteichthyes

Answer 24

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