12. Chordates

Question 1

What is the notochord and myomeres and why are they important in chordates? 4

Answer 1

1. Notochord and myomeres 2. rigid rod along body 3. transforms into vertebrae in vertebrates - we have a notochord at embryonic stage that transforms into a spinal column 4. works with muscles to allow lateral undulations for swimming

Question 2

What is the dorsal nerve cord and why is it important in chordates? 3

Answer 2

1. dorsal relative to gut 2. opposed to invertebrates in which the nerve cord is ventral 3.often brain at anterior end of nerve cord

Question 3

What is the importnace of pharyngeal gills and the endostyle in chordates?4

Answer 3

1. breath in through mouth and water passes out over gills 2. in combination with endostyle used to filter feed 3.Cilia in openings move food towards the endostyle 4. transformation to gill arches and thyroid in higher vertebrates

Question 4

What are cepalochordates? 5

Answer 4

1. Small filter feeding marine animals 2. Also known as lancelets, amphioxus, Branchiostoma 3. Simple morphology seen as ‘archetypal chordate’ 4. Alive today - live at shores. 5. only a few inches big

Question 5

What are the urochordates? 6

Answer 5

1. Diverse group of marine invertebrates
2. Also known as tunicates or sea squirts
3. Filter feed in roughly the same way, mostly using siphons
4. Tunicate larvae look like our early stages
5. metamorphosis from chordate-like larva to sessile adult form involves digesting own brain
6. Thaliaceans are pelagic, colonial with some asexula repro

Question 6

What are the two groups of vertebrates? 2

Answer 6

1. jawless/cyclostomata/agantha
2. jawed/gnathostomata

Question 7

What are the differenced between chordate and vertebrate anatomy? 10

Answer 7

Vertebrates have extra specialisation related to senses, locomotion and physiology,

Question 8

What is special about vertebrate development? 10

Answer 8

1. Neural crest, a migratory multipotent cell population, forms many structures that are specific to vertebrates
2. Peripheral nervous system -Parts of the brain

3-Sensory capsules

4-Endocrine glands

5. Parts of head and face
6. Pigment cells -Parts of circulatory system
7. Teeth and jaws
8. Branchial skeleton

Question 9

What is special about vertebrate genes? 6

Answer 9

1. Have Hox genes - related to development pattern of body
2. Amphioxus had one set
3. duplication event, leading to hypothetical jawless vertebrate ancestor
4. thought to be key reason for diversification and success of vertebratesw
5. may be a safe back up in case a gene mutates, allowing for more experiementation
6. the a second duplication event (4 sets) gave rise to modern vertebrates eg. mice

Question 10

What are lampreys (lawless vertebrates)? 6

Answer 10

1. Formal name for group: Petromyzontida
2. Eel-like (anguilliform) morphology - convergent
3. Parasitic freshwater-marine lifecycle - breed in freshwater
4. Semelparity (single breeding event)
5. No bone or jaws, just cartilages
6. suck blood of fish

Question 11

Decribe lamprey anatomy. 6

Answer 11

1. Oral sucker with keratinous teeth
2. Sucking velum apparatus
3. Dorsal nasohypophysial opening - like a nostril on top of head
4. 7 gill pouches with branchial cartilage
5. Brain, cranium and sensory organs that are homologous with ours
6. Arcualia (vertebrae) - cartilaginous and sit on nerve cord

Question 12

Describe lamprey development. 5

Answer 12

1. Larval stage: ammocoete
2. Infaunal filter feeder
3. Blind and lacks oral sucker
4. Anatomically similar to cephalochordates
5. Metamorphosis to adult stage

Question 13

Describe the hagfish (jawless vertebrates). 6

Answer 13

1. Formal name for group: Myxinoidea
2. Eel-like (anguilliform) morphology
3. Blind deep marine scavenger/predator
4. Unique gelatinous slime and twisting escape - slime bands secrete mucus that expands quickly and forms knot that moves along body
5. No bone or jaws, just cartilages
6. Burrow into carcasses and eat their way out

Question 14

Decribe hagfish anatomy. 6

Answer 14

1. Tentacles and rasping keratinous teeth
2. Velum and tongue apparatus
3. Anterior single nasal opening
4. Multiple gill pouches (5-16 pairs)
5. Simple brain and sense organs - no cranium
6. No vertebrae

Question 15

Describe hagfish development. 4

Answer 15

1. Very little know about hagfish
2. Eggs hard to grow in a lab environment
3. Discovery of neural crest in 2007
4. Reconstruction of craniofacial development in 2013

Question 16

Describe the anatomy of jawed vertebrates. 6

Answer 16

1. Pectoral and pelvic fins, homologous with arms and legs
2. Bone and dentine
3. Hinged jaws
4. Paired nostrils
5. Ribs and ventral vertebrae
6. Internal gill arches

Question 17

What groups are included in the jawed vertebrates? 4

Answer 17

1. cartilaginous fish
2. boney fish
3. lobe finned fish
4. tetrapods

Question 18

What is the traditional view of chordate phylogeny? 4

Answer 18

This is based on morphology and some genetics

Question 19

What is the modern view of chordate phylogeny?

Answer 19

1. This is absed on whole genome analysis
2. Suggests that in some cases there has been a loss of characteristics and genome simplification

Question 20

What is the traditional view of vertebrate phylogeny?

Answer 20

1. This is based on the apparenty degeneracy of hagfish - but they are not vertebreates

Question 21

What is the view of vertebrate phylogeny based on morphology and physiology?

Answer 21

Question 22

What is the modern view of vertebrate morphology, based on benetic and microRNA analysis?

Answer 22

Question 23

What can we learn from cyclostome fossils? 9

Answer 23

1. Soft-bodied so few of them
2. We have one hagfish
3. There are some cambrian fossils that may be chordate relatives
4. Pikaia has possible sigmoidal myomeres, dorsal fin, notochord? But looks like annelid. Morris and Caron 2012
5. Metaspriggina has notochord, post anal tail, paired eyes, gill bars? Moris and Caron 2014
6. Myllokunmingia has paired eyes, nasal sacs, arcualia, gill pouches and dorsal fin, clearly fishy, Shu et al. 2013
7. Yunnanozoan has possible pharynx and endostyle and disputed muscles, looks like nothing alive but seems to have gill slits
8. Cathaymyrus has some muscle bands and gill slits? Shu et al, 2006
9. there many interpretations of the phylogeny of these and no consenus

Question 24

What are the limitations of studying soft-bodied fossils? 9

Answer 24

1. Taphonomy- study of fossilisation
2. Decay and preservation can alter the appearance of fossilised beings
3. A lot of information may be lost so can’t just compare anatomy to that of living beings
4. decaying organisms may lose syanamorphies and appear more primitive
5. Cathaymyrus only has decay resistant characters and looks rotten: Potentially any chordate
6. Cartliage decays early, nerves are more robust
7. Haikouichthys has some decay prone vertebrate characters but no skull: True stem-vertebrate
8. If there was a skull, we would usually expect to see it
9. some fossils cast aside as cannot be useful