Lecture 21

Question 1

Vertebrata

Answer 1

chordates with vertebrae, previously called Craniata, includes largest animals

Question 2

6 vertebrate character states

Answer 2

1. vertebral column
2. 2 or more sets of Hox genes
3. neural crest cells
4. endoskeleton and pronounced cephalization
5. modifications to circulatory system
6. pharyngeal clefts function as gill slits ancestrally (in aquatic)

Question 3

vertebral column

Answer 3

chain of skeletal elements (cartilage or bone) surrounding and protecting nerve cord, replaces
notochord in rigidity, provides attachment sites for muscles and other skeletal elements

Question 4

Hox genes in vertebrates

Answer 4

2 or more sets, result of ancestral mutation that duplicated the set of genes (non-vertebrate chordates have only 1 set)

Question 5

neural crest cells

Answer 5

clusters of embryonic cells that form near dorsal margins

of closing neural tube, contribute to formation of bones and cartilages of cranium and other structures

Question 6

cranium

Answer 6

brain encased in protective plates

Question 7

vertebrate modifications to circulatory system

Answer 7

1. closed circulatory system with a pumping heart
2. haemoglobin in red blood cells
3. oxygenated by passing close to gills or lungs

Question 8

Pikaia

Answer 8

from Burgess Shale, vertebrate from Cambrian, but no obvious cranium or clear vertebrae

Question 9

Haikouichthys

Answer 9

Cambrian fossil with braincase and definite eyes, no clear vertebrae

Question 10

agnathans

Answer 10

jawless vertebrates, no paired fins

Question 11

2 classes of agnathans

Answer 11

1. myxini

2. petromyzontida

Question 12

myxini

Answer 12

hagfish, very small cartiaginous vertebral elements, cartilaginous cranium and other skeletal elements, protect themselves by exuding slime, some overfished for skin

Question 13

myxini feeding

Answer 13

1. grip flesh using keratinous plates in mouth
2. tie body into knot
3. slide knot forwards until braced against
   flesh
4. pull off chunk

Question 14

petromyzontida

Answer 14

lampreys, notochord surrounded by cartilaginous tube, primitive vertebral column, eyes with lenses, no jaws, larval lampreys like cephalochordates (suspension feeders), adults are parasites of fish,

Question 15

gnathostomes

Answer 15

vertebrates with jaws, 2 pairs of fins, 4 clusters of Hox genes

Question 16

origin of jaws

Answer 16

modifications of 2 pairs of skeletal rods that supported anterior pharyngeal slits, posterior slits became specialized for gas exchange (gill slits)

Question 17

chondrichthyes

Answer 17

sharks, rays, chimeras, endoskeleton made of cartilage, bony teeth, called cartilaginous fishes, ancestors with bony skeleton

Question 18

fish

Answer 18

paraphyletic group including any completely aquatic vertebrate that uses gills for respiration (includes jawless fishes, cartilaginous fishes, and bony fishes)

Question 19

cartilaginous skeletons

Answer 19

during development of most vertebrates, skeleton is
first cartilaginous and then becomes ossified (replacement of cartilage by calcium phosphate), chondrichthyans skip this developmental step

Question 20

sharks

Answer 20

pectoral fins add lift, gain buoyancy by storing oil in liver, teeth homologous to jagged scales on rough skin, teeth continuously replaced, detect changes in electrical fields generated by muscular movement via pores around head, detect vibrations in water via lateral line, cloaca

Question 21

shark reproduction

Answer 21

sperm transfer through copulation (males have pelvic fins modified as claspers), oviparous species protect eggs in leathery case, viviparous species nourish young through placenta, milk-like secretions, or eating other eggs, two feed on zooplankton

Question 22

cloaca

Answer 22

reproductive tract, excretory system, and digestive

system all exit through same opening

Question 23

rays and skates

Answer 23

swim by flapping large pectoral fins (rather than tail propulsion), flat plate-like teeth for grinding prey

Question 24

chimeras

Answer 24

flat tooth plates for crushing shelled prey, called ‘chimeras’ because they look like they were constructed by putting together bits of other fishes

Question 25

sharks as entertainment and food

Answer 25

shark watching, dorsal fin removal, low reproductive rate makes overfishing a concern