In biology, embryonic development is classified into two kinds on the basis of the complex animals and can be given as deuterostomes and protostomes. One of the major differences seen in both the development types is the development of blastopore which is also the first opening of the animal’s embryo. The opening can either be the mouth as in the case of protostomes or it can be anus as in the case of deuterostomes. To know more about the Differences Between Protostomes and Deuterostomes here is a detailed guide via Vedantu that lets you know regarding the same.
Deuterostomes
The embryonic development of deuterostomes goes through radial cleavage. While the blastula is forming via cleavage of the embryo, the cell division process occurs in radial. In this group of animals, the initial cavity created by the blastopore matures as the anus of the organism. Also, the mouth of the concerned organism is created on the other side after the formation of the anus.
Based on the similarities of structure, the following clades of deuterostomes animals are available-
Echinodermata
Echinodermata is exclusively identified as marine animals. The adult echinoderms are recognisable by the radial symmetry.
Example: Sea cucumbers, Starfish, Sand dollars, Sea lilies, etc.
Chordates
It includes both terrestrial and marine animals.
Example: Frog, Tiger, Bat, Turtle, Snake, Jawless fish, etc.
Cephalochordata
They are small marine organisms with segmented bodies.
Example: Lancelets.
Urochordata
They are also sea animals and known as Tunicata.
Example: Sea squirts, Thaliacea, Ascidians, Larvacea, etc.
Vertebrata
It includes all animals that fall under subphylum vertebrates.
Example: humans, Birds, Amphibians, Fish, etc.
Hemichordata
Hemichordata is a marine species and can be grouped as sister organisms of echinoderms.
Example: Graptolithina, Acorn worm, Pterobranchia, etc.
Protostomes
include the lower invertebrate species in which the formation of the mouth happens before the creation of the anus during embryo development. These animals have determinate and spiral cleavage and through the dividing of mesoderm their coelom forms.
Some examples of protostomes are octopuses, squid, snail, centipedes, millipedes, spiders, butterflies, ants, bees, earthworms, clams, oysters, etc.
Thus, the fundamental difference between protostomes and deuterostomes animals is the conversion of blastopore into the mouth or anus.
Differences between Protostomes and Deuterostomes
Thus, the difference between protostomes and deuterostomes lies in the position of their organs. In deuterostomes, the blastopore transforms into an anus, and another cavity on the opposite side creates a mouth. However, in protostomes, the mouth is created from the blastopore.
To learn about the difference between protostomes and deuterostomes in-depth, go through the study materials available on Vedantu’s website. For quick learning, download our Vedantu app.
Cleavage Types are Seen in Both Deuterostomes and Protostomes
The two classes differ entirely in the types of cleavages that they undergo while the formation of blastopore takes place. The cleavage that is seen can be of two types:
Determinate cleavage is also called mosaic cleavage
indeterminate cleavage is called regulative cleavage.
1. Protostomes:
These undergo the determinate type of cleavage during the formation of the blastopore. During this type of cleavage, the developmental fate of cells is already determined during the early stages of the embryo.
2. Deuterostomes:
Deuterostomes on the other hand have an indeterminate type of blastomere cleavage. In this type, the fate of the cells is not set and will only be decided after each cell is formed. It is also seen that any of the cells present in the blastopore has an equal potency to become any of the cell types that the cell wants to be. This condition is specifically called the pluripotency of the cells where each cell can undergo a different function.
Characteristics of Protostomes:
Protostomes are also referred to as schizocoelomates as the coelom is developed by splitting the solid mass of embryonic mesoderm
In protostomes, the gut is tunnelled through the embryo and it reaches up to the anus
Protostomes are said to be multi-ciliated cells.
FAQs on Differences Between Protostomes and Deuterostomes
1. What is the primary difference between protostomes and deuterostomes?
The primary difference between protostomes and deuterostomes lies in their embryonic development, specifically the fate of the blastopore. In protostomes (from Greek, meaning "first mouth"), the blastopore develops into the mouth. In deuterostomes (meaning "second mouth"), the blastopore develops into the anus, and the mouth forms later at the opposite end of the embryo.
2. Which animal phyla are examples of protostomes and deuterostomes?
These developmental patterns classify major animal groups.
- Protostome examples include phyla like Annelida (earthworms, leeches), Mollusca (snails, clams, octopuses), and Arthropoda (insects, spiders, crustaceans).
- Deuterostome examples include phyla like Echinodermata (starfish, sea urchins), Hemichordata (acorn worms), and Chordata (fishes, amphibians, reptiles, birds, and mammals, including humans).
3. How does embryonic cleavage differ between protostomes and deuterostomes?
The pattern of cell division (cleavage) in the early embryo is a key distinguishing feature:
- Protostomes typically exhibit spiral cleavage, where the dividing cells are offset from the cells below them, creating a spiral pattern. This cleavage is also determinate, meaning the developmental fate of each cell is fixed very early.
- Deuterostomes exhibit radial cleavage, where the dividing cells are aligned directly above one another. This cleavage is indeterminate, meaning that early embryonic cells are not fated and retain the potential to develop into a complete organism if separated.
4. What is the difference in how the coelom (body cavity) forms in protostomes and deuterostomes?
The formation of the true body cavity, or coelom, also differs significantly. In many protostomes, the coelom forms through a process called schizocoely, where a solid mass of mesodermal tissue splits apart to form the coelomic cavity. In deuterostomes, the coelom forms through enterocoely, where folds of the archenteron (the embryonic gut) grow outwards and pinch off to form the coelomic cavity.
5. Are humans protostomes or deuterostomes, and why?
Humans are deuterostomes. As members of the phylum Chordata, we exhibit the key developmental characteristics of this group. During our embryonic development, the blastopore forms the anus, our cleavage pattern is radial and indeterminate, and our coelom forms via enterocoely. This places us firmly within the deuterostome lineage alongside other vertebrates and echinoderms.
6. What is the biological significance of indeterminate cleavage in deuterostomes?
The indeterminate cleavage in deuterostomes is biologically significant because it allows for greater developmental flexibility. Since the fate of early cells is not fixed, each cell has the potential to form a complete embryo on its own. This is the biological basis for the natural occurrence of identical twins in humans and other deuterostomes, where a single embryo splits into two, and each part develops into a complete individual.
7. Despite their differences, what important biological features do protostomes and deuterostomes share?
Although their developmental paths diverge, both protostomes and deuterostomes share several advanced biological features. Both groups are bilaterally symmetrical, meaning they have a distinct left and right side. They are also triploblastic, possessing three primary germ layers (ectoderm, mesoderm, and endoderm) during development. Most members of both groups also possess a true coelom and a complete digestive tract with a separate mouth and anus.
8. If protostome development involves schizocoelous coelom formation, how are acoelomate animals like flatworms (Platyhelminthes) classified?
This is an excellent question that highlights evolutionary complexity. Flatworms (Phylum Platyhelminthes) are classified within the protostome lineage based on other developmental and molecular evidence, such as spiral cleavage. However, they are acoelomates, meaning they lack a true body cavity. It is believed that their acoelomate condition is a derived or possibly a primitive trait within the protostome group. Their ancestors may have had a coelom that was subsequently lost during evolution, or they may have diverged before the evolution of a true coelom was established in other protostomes.
