B3 Vertebrates

Question 1

Chondrichthyes

Answer 1

970 living species, prismatic calcification of endoskeleton cartilage, pelvic claspers. Marine predators dominant in ancient seas.

Question 2

Subclass Elasmobranchii

Answer 2

5-7 gill openings, dermal and placoid scales. Upper jaw is not fused to cranium. Ribs, spiracle and several radiations (all extinct except Neoslelachii, ‘new sharks’).

Question 3

Division Neoselachii

Answer 3

Triassic. Overhanging mouth with jaw modifications. Calcified vertebral centra replace, unconstructed notochord. Basal fin supports (fused, flexible with horny rays). Sexual dimorphism and internal fertilisation. Electroreception, oil accumulation for buoyancy.

Question 4

Neoslachii subdivisions

Answer 4

Selachii (sharks, 8 orders), Batoidea (rays, 5 orders)

Question 5

Shark features

Answer 5

Side gill slits, pectoral fin goes up to head but not attached, anal fin. Most diversity in ground or dogfish sharks.

Question 6

Ray features

Answer 6

Ventral gill slits, no anal fin, large miracle positioned dorsally. Mostly skates and stingrays in terms of species.

Question 7

Order Carcharhiniformes (requiem sharks)

Answer 7

224 species, tropical and subtropical, nearshore species. Include cat shark, hammerhead and bull shark.

Question 8

Order Lamniformes (macherel sharks)

Answer 8

15 species, offshore and pelagic. Include mako, white, thresher and basking sharks.

Question 9

Order Squalifromes (dogfish sharks)

Answer 9

97 species, mostly cold water, successful in North Atlantic. North Pacific and deep sea.

Question 10

Order Rajiformes (skates)

Answer 10

285 species, deep water and high latitude, 2 dorsal fins, long slender claspers, dorsally depressed.

Question 11

Order Myliobatiformes (stingrays, eagle rays)

Answer 11

183 species, inshore and tropical. Tail spine. Short, stout and cylindrical claspers, dorsally depressed.

Question 12

Whaleshark

Answer 12

Largest rayfin fish, 12m in length. 20% rayon fish are over 2m in length. Smallest rayfin fish (17cm, Etmopterus perryi)

Question 13

Habitats

Answer 13

shallows and tropical waters. mainly coastal marine (5% open ocean, 5% freshwater). Shadow waters, rarely less than 3000m. Mostly outside of environemtnal extremes.

Question 14

Anguilliform swimming

Answer 14

eel-like, most efficient swimming, optimise scales to reduce drag and turbulence. Dorsal fins and tail are spaced to optimise movements. They cant regulate buoyancy so they store oil instead.

Question 15

Rajiform swimming

Answer 15

Undulating pectoral finds, rays mostly.

Question 16

Buoyancy device

Answer 16

No gas bladder, heterocercal tail which creates lift, pectorals to adjust pitch. Light skeleton, slightly negatively buoyant.

Question 17

Metabolism and growth rate

Answer 17

Low metabolic rate and aerobic scope. Low food requirements (every 6 weeks or even 1 per year). Slow growth and long lifespans.

Question 18

Feeding

Answer 18

Almost all carnivorous (live prey, scavengers), or planktivorous, often feed nocturnally. Strong bite with underslung jaw, teeth are for piercing/slicing/crushing (dentition replacements). Some have enlarged orobranchial cavities (suction), or protrusion of palatoquadrate (bite speed/strength).

Question 19

Feeding/hunting examples

Answer 19

Tailfin (threshers) use herding/stunning. Sawsharks use slashing. Torpedo rays stun via electricity. Manta rays use cephalic horns to guide prey.

Question 20

Sensory physiology

Answer 20

Often nocturnal, so rely on visual senses. High olfactory sensitivity, good vision in day. Mechanoreception, acoustic sensitivity, electroreception, large brain.

Question 21

Reproduction

Answer 21

Few large offsprings with large investments (high energy) low fecundity, large/precocial young). Mature at 6-18 years. Internal fertilisation, all nutrition from yolk sac (obi/viviparity). Can additionally include omophagy (eat eggs of brother), placental viviparity, uterine secretions.

Question 22

Subclass Holocephali (chimeras)

Answer 22

33 species, deep water. Gill chamber is further forward, no spiracle. 1 opercular opening, covering 4 gill openings. Upper jaw is fused to cranium, no protrusible. Teeth have continuous growth, no replacement. Naked skin (modern forms). Claspers on head and pelvis. Venomous spine, in front of 1st dorsal fin. No stomach or ribs, tail often diphycercal (pointed).