The key difference between Protostomes and Deuterostomes is that in protostomes blastopore becomes the mouth while in deuterostomes it becomes the anus. Another major difference is that embryos of protostomes undergo spiral cleavage while embryos of deuterostomes undergo radial cleavage.
In understanding these two terms it would be important to pay attention to how the embryonic development of organisms takes place. It would be particularly important to consider animals with a coelom, which is a fluid-filled cavity lying between endoderm (gut) and mesoderm (mostly muscle layer); in other words, coelom is the peritoneum in mammals. Protostomes and deuterostomes are the two main types of coelomate animals, and there are many differences between them. They primarily differ in the way their mouth and anus are formed during embryonic developments.
CONTENT
1. Overview and Key Difference
2. What are Protostomes
3. What are Deuterostomes
4. Similarities Between Protostomes and Deuterostomes
5. Side by Side Comparison – Protostomes vs Deuterostomes in Tabular Form
6. Summary
What are Protostomes?
Protostomia in Greek means the mouth first, as the blastopore eventually becomes the mouth in protostomes. In other words, the small pore formed during the embryonic developments becomes the mouth in the animals of this type. Protostomes include animals such as Platyhelminthes, Molluscs, Arthropods, Annelids, Nematodes, and many other lower phyla. Among most of the protostomes, the coelom is formed via splitting a solid mass of the embryonic mesoderm; hence, they are called schizocoelomates. There are only very few groups such as Priapulids that do not have a coelom.
Another most prominent characteristic of protostomes is that their embryos undergo spiral cleavage. Cells formed through the spiral cleavage are determinate, which means the fate of each cell formed is resolute. In addition, there are three major groups within protostomes: Superphyla: Ecdysozoa, Platyzoa, and Lophotrochozoa. The classification of these three groups is based on the data of the recent molecular studies on the embryonic development of protostomes.
What are Deuterostomes?
Deuterostomes are the animals whose embryonic development undergoes radial cleavage. That means, the cell division planes take place radially during the formation of the blastula through cleavage of the fertilized egg embryo. The Greek term deuterosmomia means that the mouth comes second, which means the anus comes first. Blastula undergoes gastrulation after formation. During the gastrulation, blastopore becomes anus in deuterostomes. After the formation of the anus, another cavity called archenteron runs through the gut, leading to the formation of the mouth in deuterostomes. The archenteron has longitudinal cavities and those become the coelom in deuterostomes. Therefore, they are called enterocoelus animals.
Figure 01: Protostomes and Deuterostomes
There are two deuterostome phyla as Echinodermata and Chordata. Therefore, animals in the most developed or evolved phyla in the Kingdom Animalia are deuterostomes.
What are the Similarities Between Protostomes and Deuterostomes?
- Both Protostomes and Deuterostomes are coelomates.
- Both groups belong to Kingdom Animalia.
What is the Difference Between Protostomes and Deuterostomes?
Protostomes include many invertebrates while deuterostomes include echinoderms and chordates. The fate of blastopore is different in these two groups. In the former, the blastopore develops into the mouth while in the latter, the blastopore develops into the anus. Furthermore, embryonic development occurs via spiral cleavage in protostomes while it occurs via radial cleavage in deuterostomes.
Body parts of deuterostomes are more evolved and sophisticated than protosomes. Moreover, there is a difference between the two in terms of the formation of archenteron, nerve cord, as well as cell development. Nerve cord in protostomes is ventral while nerve cord in deuterostomes is dorsal. Archenteron forms in deuterostomes, but not in protostomes. In addition, cell development in protostomes is determinate.
Summary – Protostomes vs Deuterostomes
Protostomes and Deuterostomes are two groups of coelomates. The difference between protostomes and deuterostomes is mainly based on the fate of blastopore and cleavage during embryonic development.
Reference:
1.“IASZoology.com.” Appointment, Available here.
2. “Deuterostome.” Wikipedia, Wikimedia Foundation, 21 May 2018, Available here.
Image Courtesy:
1.”Protovsdeuterostomes” By WYassineMrabetTalk✉This vector image was created with Inkscape. – Own work (CC BY-SA 3.0) via Commons Wikimedia
Mayr’s book WHAT EVOLUTION IS. From the chart on page 52, it would appear that protostome and deuterostome were simultaneous events; but apparently, there was a 60 million year difference between the split from protostome to deuterstome. (Mayr, page 60) And without this split chordates could not exist; hence, homo-sapiens would not be possible…