The key difference between protostomes and deuterostomes is that protostomes have spiral and determinate cleavage, with the blastopore forming the mouth first, while deuterostomes have radial and indeterminate cleavage, with the blastopore forming the anus first.
What are Protostomes?
“Protostomes are a major evolutionary group of animals characterized by their embryonic development, where the first opening formed during gastrulation becomes the mouth, and they typically exhibit spiral and determinate cleavage.”
This is in contrast to deuterostomes, another major group of animals, where the first opening becomes the anus and a second opening later develops to form the mouth.
The protostomes include several well-known phyla, such as Arthropoda (insects, spiders, crustaceans, etc.), Mollusca (snails, clams, squids, etc.), Annelida (earthworms, leeches, etc.), and others. These animals display a diverse range of characteristics and adaptations, making them one of the most successful and abundant groups in the animal kingdom.
What are Deuterostomes?
“Deuterostomes are a major group of animals where the first opening during embryonic development becomes the anus, and they exhibit radial and indeterminate cleavage. Examples include chordates (vertebrates) and echinoderms.”
Deuterostomes are a major evolutionary group of animals that share certain developmental characteristics. They belong to the larger category of Bilateria, which includes animals with bilateral symmetry. Deuterostomes are distinguished by a specific pattern of embryonic development, known as deuterostomy.
During deuterostome development, the first opening that forms in the embryo becomes the anus, and the second opening becomes the mouth. This process is in contrast to protostomes, another major group of Bilateria, where the first opening becomes the mouth and the second becomes the anus.
Deuterostomes include several diverse and well-known animal phyla, such as:
Chordates
This phylum includes vertebrates (animals with backbones) and some closely related invertebrates. Examples of chordates include fish, amphibians, reptiles, birds, and mammals (including humans).
Echinoderms
This phylum includes animals like sea stars, sea urchins, and sea cucumbers. They are characterized by spiny skin and a unique water vascular system used for movement and feeding.
Hemichordates
This is a lesser-known phylum that includes acorn worms and pterobranchs, typically found in marine environments.
Deuterostomes play a significant role in the biodiversity of the animal kingdom and have adapted to various ecological niches, ranging from marine to terrestrial habitats. Their evolutionary history and unique developmental characteristics provide valuable insights into the diversity and complexity of life on Earth.
Protostomes Vs Deuterostomes
The main differences between protostomes and deuterostomes are given below:
| Characteristic | Protostomes | Deuterostomes |
| Embryonic development | Deuterostomy: First opening becomes the anus, the second opening becomes the mouth. | Mesoderm buds from the archenteron form coelom. |
| Body Cavity | Schizocoelom formation. | Enterocoelom formation. |
| Cleavage Pattern | Spiral and determinate. | Radial and indeterminate. |
| Fate of Blastopore | Forms mouth first (protostome) | Forms anus first (deuterostome). |
| Coelom Formation | Solid masses of mesoderm split to form coelom. | Mesoderm buds from the archenteron to form coelom. |
| Examples | Insects, mollusks, annelids, and more. | Deuterostomy: First opening becomes the anus, and the second opening becomes the mouth. |