Vertebrate features Flashcards
Features of the vertebrates
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…
The endostyle
- 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
Differences between the invert chordates and verts
•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)
Embryological features of the verts
- Duplication of Hox gene complex - controlling development
- Development of the neural crest
- Placodes - thickenings of ectoderm, associated with the neural crest (gives rise to complex sense organs in head region etc.)
- Brain is larger and divided into 3 (fore, mid and hind)
- Increased body size and increased activity
- Mineralised tissues - unique minerals - hydroxyapatite (Ca and P)
Duplication of Hox genes…
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
Neural crest formation
Neural plate gives rise to NS - at ends of neural plate is crest tissues developing
- Invagination of ectoderm forms neural tube
- Neural crest tissues become sandwiched between epidermis and neural tube
- 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
Precursors to neural crest
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…
The vertebrate brain compared to the inverts
- 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
Increased body size and activity
- 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
Mineralised tissues evolution and benefits
•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?
Types of tissue that can be mineralised
- Mineralised cartilage
- 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 - Enamel (96% mineralised)
- Dentine (90%) - both found in teeth and exoskeletons of ancestral verts
- Enameloid - different origin to enamel, comes from meso (enamel from ecto)
- 96% forms teeth and dermal scales of cartilaginous fish - Cementum - fastens teeth in sockets - 45% mineralised
