What is the Difference Between Protochordates and Euchordates?

The main difference between protochordates and euchordates lies in their structure and evolutionary development within the phylum Chordata. Protochordates are invertebrate animals, while euchordates include vertebrates. Here are some key differences between the two groups:

Protochordates:

1. Notochord persists throughout life.
2. No cranium or vertebral column.
3. Atrium is present.
4. Heart is chamber-less, and no blood corpuscles are present in the blood.
5. Pharyngeal slits or clefts are present throughout life.
6. Endostyle, the precursor of the thyroid gland in higher vertebrates, is present except in hemichordates.
7. Absent neural crest cells in the development of the nervous system.
8. Mostly dioecious, or monoecious in most urochordates.

Euchordates (Vertebrates):

1. Notochord is replaced by the vertebral column.
2. Cranium and vertebral column are present.
3. Atrium is absent.
4. Chambered heart, and red blood cells (RBCs) are present in the blood.
5. Pharyngeal slits or clefts persist in some vertebrates.
6. Presence of neural crest cells in the development of the nervous system.
7. Sexes are separate (dioecious) except in some fishes.
8. During fertilization, the sperm unites with the ovum in the pathway of the animal pole.

In summary, protochordates are invertebrate animals with a notochord that persists throughout life, while euchordates include vertebrates that have a vertebral column replacing the notochord. These differences in structure and development have significant implications for the evolution and diversity of chordate animals.

Comparative Table: Protochordates vs Euchordates

Here is a table comparing the differences between protochordates and euchordates:

• Protochordates, also known as Acraniata, are lower chordates that lack a head and cranium. They are exclusively marine with small bodies.
• Euchordates, also known as Craniata, are higher chordates that possess a head and cranium. They can be found in both aquatic and terrestrial habitats and have larger bodies.