Gnathostomes

Question 1

what are generalised gnathostome features

Answer 1

• presence of jaw supported by gill arch
• spiracle (remnants of gill slit)
• Teeth present in jaws
• presence of nostrils which lead into olfactory bulbs

Question 2

What are chondrichthyes

Answer 2

Cartilagenous fishes

• 1 group of gnathostomes, out of 4 main groups of jawed vertebrates

Question 3

groups of gnathostomes

Answer 3

1) Placodermi + Acanthodians(extinct)
2) Chondrichthyes (cartilaginous fishes)
3) osteichythes (bony fishes)
4) tetrapoda

Question 4

what are the extinct jawed fish

Answer 4

placoderms

Acanthodians

Question 5

Placoderms

Answer 5

• 430-360 MYA
• plate skin , bony plates covered head region and some of trunk
• no modern equivalent
• vivoparity (give birth to live young)
• Variable forms , some dorsoventrally flattened

Question 6

Acanthodians

Answer 6

• “spiny sharks”
• spines on body , some toothless and some had teeth
• very similar to teeth found in sharks today
• possible basal group to cartilaginous fishes
• not very large

Question 7

Chondrichthyes

Answer 7

• First appeared 400 MYA
• Cartilaginous skeleton
• Lipid - filled liver
• High blood urea concentration
• Most hyostylic jaw suspension

Question 8

Advantage of cartilaginous skeleton and lipid filled liver

Answer 8

1) Cartilaginous skeleton - highly advantageous as they are very heavy bodied, served to lighten the body and make it v moveable

2) Lipid filled liver - can make up to 25% of animals body weight
- lipids can lighten body = no swim bladder needed
- liver size varies depending on where they live

• E.g. small liver for benthic living and large liver for open water swimmers

Question 9

Advantages of High blood urea concentration

Answer 9

1) High blood urea conc - makes organism either isotonic or hyperosmotic with sea water, can make them less dense and more buoyant

Question 10

hystolic

Answer 10

upper jaw is fused to cranium

Question 11

Sub groups of chondrichthyes

Answer 11

1) Holocephali (e.g. rat fish chimaera)

2) Elasmobranchs (sharks, skates + rays)

Question 12

Holocephali (e.g. rat fish chimaera) features

Answer 12

• found in deep water
• whip like tail + well developed pectoral fins
• can only move lower jaw (hystolic) , feeds on crustaceans and needs hard surface to crush them against
• rich in mechanoreceptors and electroreceptors for detection in water

Question 13

claspers

Answer 13

reproductive organ

Question 14

Features of sharks

Answer 14

1) Vary in size e.g. cookiecutter shark (20cm) -> great white
2) Vary in shape e.g. hammer head shark, head shape allows for “binocular visions” - can identify depth
3) personality traits, some sharks show preferences between hanging out in groups or being solitary

Question 15

galeomorphs

Answer 15

having an anal fin

Question 16

squalomorphs

Answer 16

no anal fin

Question 17

what are batoidea

Answer 17

skates + rays

Question 18

Features of batoidea

Answer 18

1) dorsoventrally flattened - associated with benthic lifestyle
2) Mouth + gills underneath , spiracle draws water in and out through gills
3) Pertruding jaw+ crushing teeth for feeding on molluscs
4) enlarged pectoral fins for swimming

Question 19

differences between rays and skates

Answer 19

1) skates have dorsal fins on tail, rays don’t but sometimes have a barb
2) skates lay eggs, rays give birth to live young
3) Manta ray - largest at 6m in size, filter feeder has fins that direct water into mouth
4) some of both produce electric currents, skates use low currents from tail for communication, electric rays have powerful currents used in predation

Question 20

General features of cartilaginous fishes

Answer 20

1) short intestine - feed on mainly meat, short gut for processing
2) paired fins - heterocercal tail (asymmetrical) gives thrust and lift for heavy body

Question 21

what are placoid scales

Answer 21

• found in shark they are dentacles , homologous of teeth
• different shapes and arrangements in different species
• pitted + rough feeling, thought to help with water flow (hydrodynamic)

Question 22

Sharks are covered In dentacles (placoid scales), is this the same for skates + rays

Answer 22

• No skates + rays don’t have dentacles all over body, just in some places
  1) dentacles is in one form - forms poisonous barb (sting ray)
  2) Dorsal mid line of dentacles - skates

Question 23

How do teeth form in sharks

Answer 23

• lack dermal bone so teeth form within skin
• can easily replace damaged teeth

4 types

• Tooth whorl
• pleurodont
• acrodont
• thecodont

Question 24

what sensory systems are present in sharks

Answer 24

1) Mechanoreceptors - detect vibrations
2) Chemoreceptors - acute sense of smell , olfactory bulbs , larger they are better sense of smell
3) Electroreceptors - Ampullary organs , detect electrical impulses from prey (found in heads of shark and pectoral fins of skates and rays)
4) Vision - well adapted for low light intensities

Question 25

how does the great white kill

Answer 25

by exsanguination (loss of blood)

Question 26

reproduction strategies for sharks

Answer 26

• very successful
• males have modified chasers on pectoral fin
• geared up for animals that live a long time and invest a lot in offspring/reproduction later on in life