Protostomes vs Deuterostomes
In understanding these terms, it would be important to pay attention into how the embryonic development of organisms takes place. It would be particularly important to consider the animals with a coelom, which is the 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.
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 including 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 as schizocoelomates. There are only very few groups such as Priapulids that do not have a coelom.
A most prominent characteristic of the protostomes is that their embryos undergo the spiral cleavage. Cells formed through the spiral cleavage are determinate, which means the fate of each cell formed is a resolute. In addition, it would be important to state that there are three major groups within protostomes known as Superphyla: Ecdysozoa, Platyzoa, and Lophotrochozoa. The classification of those three groups has been based on the data of the recent molecular studies on embryonic development of protostomes.
Deuterostomes are the animals with their embryonic development encounters through radial cleavage. That means the cell division planes are taking place radially during the formation of the blastula through cleavage of the fertilized egg, aka embryo. The Greek term deuterosmomia means that the mouth comes second, which means the anus comes first. After the formation of the blastula, it goes through the gastrulation, and the blastopore is formed that becomes the anus. After the formation of the anus, another cavity called archenteron runs through the gut leads to form the mouth in deuterostomes. The archenteron has longitudinal cavities and those become the coelom in deuterostomes. Therefore, they are called enterocoelus animals. This means that there is only one type for the formation of the coelom in deuterostomes.
There are two deuterostome phyla known as Echinodermata and Chordata. Therefore, it could be concluded that animals in the most developed or evolved phyla in the Animal Kingdom are the deuterostomes. When these two phyla are considered, one (Echinodermata) belongs to the group of invertebrates.
What is the difference between Protostomes and Deuterostomes?
• Protostomes contain more phyla and species than deuterostomes do.
• Mouth is formed from the blastopore in protostomes while that leads to form the anus in deuterostomes.
• Protostomes have a spiral cleavage whereas deuterostomes have a radial cleavage.
• Fate of the cells formed through cleavage is determined in protostomes but not in deuterostomes.
• Deuterostomes are more evolved and sophisticated with body parts than the protostomes.
• Protostomes contain both schizocoelomates and priapulids, whereas deuterostomes are always enterocoelus.
• Archenteron is formed in deuterostomes but not in protostomes.