phylum chordata

Question 1

defining features of chordata

Answer 1

• notochord
• muscular post-anal tail
• dorsal, hollow nerve cord
• pharyngeal slits or clefts

Question 2

cephalochordata ( lancelets )

Answer 2

• 2 species in shallow sea
• filter feed using mucus net
• show the 4 defining features both as larvae and adults

Question 3

urochordata ( tunicates )

Answer 3

• marine filter feeders. 410 species
• planktonic larva is clearly a chordate
• adults are sessile and benthic

( pharynx with numerous slits )

Question 4

the 2R hypothesis

Answer 4

a hypothesis that the genomes of the early vertebrate lineage underwent two complete genome duplications, and thus modern vertebrate genomes reflect paleopolyploidy

• where cephalochordates and tunicates have a single gene, vertebrates often have two to four equivalent genes:
  • result of two whole-genome duplication events
  between 564 and 450 MYA
• may explain the diversity of vertebrates
  •gene duplication is one of the most important
  evolutionary forces

Question 5

vertebrata ( vertebrates )

Answer 5

• 62000 species
• recent discoveries of early vertebrates from lower
  cambrian ( 530 MYA )
• similar to cephalochordates, but with :
  • large brain
  • skull
  • eyes
  •’teeth’

Question 6

Myxini ( hagfish )

Answer 6

• 87 species, all marine scavengers
• agnathans : without jaw
  •feed by knotting and using teeth-like processes
  on tongue
• cartilaginous skeleton
• well developed notochord
• probably cambrian
• slime glands

Question 7

petromyzontida ( lampreys )

Answer 7

• 47 species, marine and freshwater
• agnathans : without jaws
• larvae filter feeders, adults parasitic or do not
  feed
• notochord and simple vertebral column

Question 8

evolution of jaws

Answer 8

• jaws allow efficient feeding and a wider range of food items
• jaws well represent in early silurian
  • probaly evolved in ordovician ( 500-440 MYA )
• 4 clades:
  • chondrichthyes
  • placoderms (extinct)
  • acanthodians (extinct)
  •osteichthyes

Question 9

chondichthyes

Answer 9

sharks, skates, rays and chimera

almost exclusively marine
- some can live in freshwater ( e.g bull shark )

Question 10

chondichthyes : characteristics

Answer 10

• cartilagenous skeleton reinforced with small bone
  playtes
• well developed jaws and paired fins
• well developed sence of smell and lateral line
  system
• no swim bladder
• all carnivores
• all have interan fertilisation
  • males have modified pelvic fins to transfer
  sperm to female
• development
  • ranges from ovipary ( e.g dogfish ) to vivipary
  ( e.g bronze whaler shark )
• few offspring

Question 11

actinopterygii

Answer 11

( fin fish )
sturgoen, paddlefish, birchir, gaars, bowfin, ray-finned fish

global distribution and very abundant in all aquatic systems

Question 12

actinopterygii : characteristics

Answer 12

• ossified endoskeleton (i.e bones)
• skin covered in scales and mucus
• swim bladder
• teleosts
• fins supported by rays
• jaw modificatins
• most have external fertilisation and pealgic larvae hatch from the eggs
  •therefore produce huge numbers of eggs
• some species do show parental care
• a few are ovoviviparous ( e.g guppy ) or viviparous ( e.g surf perch )

Question 13

actinistia ( coelacanths )

Answer 13

• 2 living species
• discovered in 1938 after an 80 million year absence
• fleshy fins
• hinged skull
• ovoviviparous

Question 14

dipnoi ( lungfish )

Answer 14

• 6 species, southern hemisphere
• live in swamps and shallow pools
• gulp air into lungs
• evolved in lower Devonian
• closest living relatives to the tetrapods

Question 15

osteichthyes

Answer 15

the ostichthyes are characterised by jaws and mineralized skeletons