The upcoming discussion will update you about the difference between protochordates and higher chordates.
Difference # Protochordates:
1. Notochord persists throughout life.
2. No cranium or vertebral column.
3. Atrium, the space in between pharynx and body wall, is present.
4. Endostyle is present except hemichordates. It is the precursor of thyroid gland of higher vertebrates.
5. Absence of neural crest cells in the development of nervous system.
6. Pharyngeal slits or clefts are present throughout life.
7. Heart chamber less. No blood corpuscles in the blood.
8. Sexes mostly separate (dioecious), or monoecious in most urochordates.
9. During fertilization, the sperm unites with the ovum in the pathway of vegetal pole.
Hemichordates, urochordates and cephalochordates.
Difference # Higher Chordates:
1. Mostly notochord is replaced by vertebral column, or in some cases notochord is persistent with vertebral column.
2. Cranium and vertebral column, both are present.
3. Atrium is absent.
4. Endostyle is totally absent in the adult stages of vertebrates, (only found in the ammocoetes larval stage of Petromyzon).
5. Presence of neural crest cells in the development of nervous system.
6. Pharyngeal slits or clefts persist in some vertebrates.
7. Chambered heart. RBC is present in the blood.
8. Sexes’ are separate (dioecious) except in some fishes.
9. During fertilization, the sperm unites with the ovum in the pathway of animal pole.
Agnathan to mammals.