Vertebrate features

Question 1

Features of the vertebrates

Answer 1

All have chordate features…
•notochord - most vertebrates lost this during development, but the jawless vertebrates retain it
•dorsal, hollow nerve chord - forms NS
•pharyngeal gill slits - in verts are used for respiration
•post-anal tail
AND - the endostyle…

Question 2

The endostyle

Answer 2

• is a ciliated groove at the bottom of the pharynx
• produces mucous in inverts helping with filter feeders
• though to be homologous with the thyroid gland of verts
• can harbour iodine (from surrounding water or blood) used to make thyroxine

Question 3

Differences between the invert chordates and verts

Answer 3

•have vertebrae (may not be that well developed in some - hagfish and lampreys which are rudiments - arcualia)
-replaces notochord and becomes the intervertebral discs
-grows around nerve chord = protection, either bone or cartilage
•presence of cranium of bone, cartilage or is fibrous
•mammals skull highly specialised for muscle attachment (not seen in all)

Question 4

Embryological features of the verts

Answer 4

1. Duplication of Hox gene complex - controlling development
2. Development of the neural crest
3. Placodes - thickenings of ectoderm, associated with the neural crest (gives rise to complex sense organs in head region etc.)
4. Brain is larger and divided into 3 (fore, mid and hind)
5. Increased body size and increased activity
6. Mineralised tissues - unique minerals - hydroxyapatite (Ca and P)

Question 5

Duplication of Hox genes…

Answer 5

Grouped together in complex/cluster - ancestral jawless vertebrates have 2 clusters
•inverts and invert chordates only have 1 cluster
•further duplications have taken place - evolution of jawed verts have 4 clusters
•further duplications in groups like the teleosts (7) and fishes like salmon (13)
-some lost along way, hence odd numbers

Question 6

Neural crest formation

Answer 6

Neural plate gives rise to NS - at ends of neural plate is crest tissues developing

1. Invagination of ectoderm forms neural tube
2. Neural crest tissues become sandwiched between epidermis and neural tube
3. Neural crest cells migrate to different parts of body & develop into different types of cells
   - these are considered as another germ layer - quadroblastic
   - responsible for structures of head, smell, vision, hearing, adrenal glands & pigment cells

Question 7

Precursors to neural crest

Answer 7

Tunicates and amphioxus have similar genes found & expressed in development for NS - to those genes for formation of neural crest
Tunicates larval stage have migratory cells that can form pigment cells…

Question 8

The vertebrate brain compared to the inverts

Answer 8

• the tunicates lost their NS
• lancelets have a brain bulge at one end of the notochord - not very defined though
• amphioxus brain not divided but has similar genes for it - except those responsible for the forebrain

Question 9

Increased body size and activity

Answer 9

• change in feeding mode as now more active
• cephalochordates up to 10cm
• jawless verts 10-100cm
• cannot rely on ciliary action or diffusion - need proper systems
• higher metabolic rate than invert chordates, more predacious etc.
• vertebrates can sustain periods of anaerobic respiration (build-up of lactic acid in the muscles - allows bursts of exercise

Question 10

Mineralised tissues evolution and benefits

Answer 10

•mixture of collagen fibres, proteinaceous tissue matrix and hydroxyA useful as hard, but light and cracks won’t spread = resilient
•more resistant to lactic acid build up than CaCO3
-hydroxyapatite evolved as more resistant to aerobic respiration?

Question 11

Types of tissue that can be mineralised

Answer 11

1. Mineralised cartilage
2. Bone - highly vascularised and can withstand breakage (vascularisation = mend selves)
   - dermal bone - grows in skin (skull)
   - endochondral bone - grows within body, initially cartilage but replaced
3. Enamel (96% mineralised)
4. Dentine (90%) - both found in teeth and exoskeletons of ancestral verts
5. Enameloid - different origin to enamel, comes from meso (enamel from ecto)
   - 96% forms teeth and dermal scales of cartilaginous fish
6. Cementum - fastens teeth in sockets - 45% mineralised