Protostomes and Deuterostomes
The animal kingdom is diverse in terms of morphology, anatomy, and physiology. Despite the differences, one thing that remains common among most animals is that they all start life as a single cell. As the organism attains maturity, it develops some unique characteristics that set it apart from others and help in the systematic classification of animals into different groups. One such group of animals are called the metazoans whose body cells are differentiated into tissues and organs. Based on the embryonic development of these metazoans, they are classified into two groups - protostomia and deuterostomia (or protostomes and deuterostomes).
Protostomes
The word protostome is derived from the Greek words “proto” meaning first, and “stoma”, which means opening or mouth. In literal terms, protostome means ‘first mouth’. The reason for this naming is based on their mode of embryonic development. When the embryo develops, the protostomes first form the mouth from the blastopore, and the anus develops later after the mouth has been created.
A protostome is a group of animals that includes invertebrates like arthropods (insects and crabs), molluscs (clams and snails), and worms of phylum Annelida. Developments in the last few decades in molecular biology techniques such as DNA sequence analysis has suggested that protostomes can be divided into two major super phyla or groups called Spiralia and Ecdysozoa. While Spiralia includes Platyhelminthes, molluscs, and annelids, Ecdysozoa comprises nematodes and arthropods.
Deuterostomes
The word deuterostorme also has a Greek origin; “deutero” means second, and “stoma” means mouth or opening. Thus, deuterostome translates to ‘second mouth’. In deuterostomes, the opening at the bottom of the gastrula, known as the blastopore, forms the anus. The mouth is formed at later stages of a deuterostome’s embryonic development. In deuterostomes, the anus and the mouth are located at the opposite ends of the blastopore, and a digestive tract develops in the middle to connect the mouth and the anus.
Deuterostomes further have three significant classifications which are - Chordata, Echinochordata, and Hemichordata. Chordata includes all the vertebrates like birds and mammals. So, are humans deuterostomes? Well, yes, they are!
Echinochordata and Hemichordata comprise invertebrates. While Echinochordata includes starfish, sea urchins, and sea cucumbers, Hemichordata contains grapholites and acorn worms.
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Difference Between Protostomes and Deuterostomes
The most significant difference between protostomes and deuterostomes arises due to the dissimilarities in their embryonic development. In protostomes, the blastopore forms in the mouth, but in deuterostomes, the blastopore is involved in the development of the anus.
Now let us go through some other striking differences between protostomes and deuterostomes:
Origin of Mouth and Anus: In protostomes, the origin of the anus is secondary, but in deuterostomes, the formation of the mouth is secondary.
Origin of Mesoderm: The archenteron is the rudimentary alimentary canal formed during the early stages of embryonic development that later forms the mesoderm and endoderm. The development of archenteron is not seen in protostomes, but, for deuterostomes, the primitive gut formation takes place in early embryos.
Late Gut Development: In protostomes, the anus is formed by tunnelling of the gut into the embryo. But in deuterostomes, the formation of the mouth is by the gut tunnelling into the embryo.
Development of Coelom: In protostomes, the body cavity of the coelom is formed by splitting the mesodermal layer. Thus, they are schizocoelomates since the coelom is created by schizocoely. On the other hand, the deuterostomes are enterocoelomates where the body cavity or the coelom is formed by the mesoderm pinching off from the gut.
Type of Cleavage: In protostomes, the kind of cleavage is determinate, meaning that the blastomere of the early embryonic stage is incapable of developing into independent embryos. But deuterostomes undergo indeterminate division whereby the early blastomeres can develop into complete embryos.
Nervous System: Protostomes have a solid, ventral nerve cord. In deuterostomes, the nerve cord is hollow, with some possessing pharyngeal gill slits.
Body Complexity: Deuterostomes have a more evolved and complex body organisation than protostomes.
Type of Cell Ciliation: The cells in protostomes are multi-ciliated, but those in deuterostomes are mono-ciliated.
Number of Phyla: Protostomes include more species and phyla compared to deuterostomes.
Classification: Protostomes can be grouped into Spiralia and Ecdysozoa. The groups under deuterostomia include Echinoderms, Chordates, Hemichordates, and other higher and more complex organisms like human beings.
Characteristics of Deuterostomes
the blastopore Develops into an anal
The mouth in deuterostomes is formed by the gut that tunnels to the embryo
Deuterostomes are Always enterococcus.
The nervous system of deuterostomes is composed of the hollow nerve cord
the body Composition is more complex as compared to protostomes
During the development phase, they go through the intermediate tree cleavage where all the Blastoma can develop into the embryos completely
Here, the animals undergo Radical cleavage
deuterostomes contain fewer phyla and species as compared to protostomes
echinoderms, hemichordates and chordates are Included in deuterostomes
For deuterostomes, Early stages of embryo formation, archenteron development takes place.
Characteristics of Protostomes
The blastopore develops into a mouth and not the anus
Bigot tunnels into an embryo and forms the anus
The Nervous System of protostomes is solid and has a ventral solid COD
Organisms of protostomes undergo determinate cleavage.
The blastopore produced in the development stages of the embryo cannot develop.
Spiral cleavage is exhibited by protostomes
Protostomes are Less evolved and more Complex than deuterostomes
There is No archenteron development
The anus arises at a secondary position
Organisms of protostomes include flatworms annelids and Arthropods
protostomes have multi ciliated cells
Subject Difficulty Level
Biology is a comparatively difficult subject than the other sections of science, due to its complexity and diversity in concepts.
However, with firm dedication and determination, all the topics can be easily tackled.
It is not to be ignored that Biology plays an important role and has a heavier weightage as compared to the other sections of science subject
Relatively more marks can be scored through Biology subject if studied thoroughly
Learning biological topics may require a lot of time at the initial stages, but once the concept is understood only regulated revision is required to Remember.
The most important tip in learning Biology is to make notes.
Always remember to make proper important notes while studying and duly revise them repeatedly so that all The detailed data is being remembered by the brain.
This topic is simple and hence cannot be neglected for studying purpose
Reproduction in Deuterostomes and Protostomes
The most common deuterostomes have separate sexes. This means the male and females are indifferent organisms of deuterostomes. So the most common method of reproduction of deuterostomes is sexual reproduction. However, there are some exceptions such as ascidians.
As protostomes fall in the higher category of animals, they reproduce sexually. They form gametes in the form of sperms for male systems and oocytes for female systems. Major protosomes are gonochoristic that is they have separate male and female individuals.
Points to Remember
deuterostomes and protostomes are two groups of coelomates
deuterostomes And protostomes are differentiated based on their formation and cleavage during the development phase
The distinction between deuterostomes and protostomes is that in deuterostomes blastopores develop into anal opening and in protostomes, blastopores develop into a mouth
protosomes are invertebrates whereas deuterostomes Have chordates
In protostomes, the mouth forms before the anus
whereas in deuterostomes the anus is formed before the formation of the mouth
Samples Questions for Exam
What are deuterostomes explain their properties?
What are protostomes and explain their properties?
Differentiate between deuterostomes and protostomes.
What are the characteristics of deuterostomes?
Advantages of being deuterostomes over protostomes.
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FAQs on Difference Between Protostomes and Deuterostomes
1. What is the fundamental difference between protostomes and deuterostomes?
The fundamental difference lies in their embryonic development. In protostomes, the first opening to form in the embryo, the blastopore, develops into the mouth ('proto' means first, 'stoma' means mouth). In deuterostomes, the blastopore develops into the anus, and the mouth is formed secondarily ('deutero' means second). This reflects a major evolutionary divergence in the animal kingdom.
2. What are some common examples of protostome and deuterostome animal phyla?
These two developmental patterns classify most major animal groups:
Protostomes include the phyla Arthropoda (insects, spiders, crustaceans), Mollusca (snails, clams, octopuses), and Annelida (earthworms, leeches).
Deuterostomes include the phyla Echinodermata (starfish, sea urchins) and Chordata (which includes all vertebrates like fish, amphibians, birds, and mammals).
3. Are humans protostomes or deuterostomes, and why?
Humans are deuterostomes. This classification is based on our embryonic development where the anus is formed from the blastopore, and the mouth develops later. As members of the phylum Chordata, we share this and other key deuterostome characteristics, such as radial cleavage and an internal skeleton.
4. How does the pattern of embryonic cleavage differ between protostomes and deuterostomes?
The pattern of early cell division, or cleavage, is a key point of difference:
Protostomes typically undergo spiral cleavage, where new cells are arranged in a spiral, fitting into the grooves between the cells below them. This is also determinate cleavage, meaning the developmental fate of each cell is fixed very early.
Deuterostomes undergo radial cleavage, where cells are stacked directly on top of each other. This is indeterminate cleavage, meaning early cells are not yet specialised and retain the potential to develop into a complete embryo if separated.
5. What is the difference in how the coelom (body cavity) forms in these two groups?
While both groups are coelomates, the method of coelom formation is distinct. In most protostomes, the coelom is formed by schizocoely, where a solid mass of the mesoderm splits apart to form the cavity. In deuterostomes, it forms by enterocoely, where the coelom develops from pouches that pinch off from the archenteron (the primitive gut).
6. Why is the fate of the blastopore so significant in animal classification?
The fate of the blastopore is not just a minor detail; it represents a fundamental split in the evolutionary path of bilaterally symmetrical animals. This single trait is strongly correlated with a whole suite of other developmental characteristics, including the type of cleavage, coelom formation, and nervous system organisation. It serves as a reliable marker for two distinct and ancient evolutionary lineages.
7. At which stage of embryonic development do the differences between protostomes and deuterostomes first become evident?
The primary differences first become evident during and immediately after gastrulation. It is during gastrulation that the blastopore is formed, and its developmental fate—becoming either the mouth or the anus—is the defining characteristic that sets these two major evolutionary lines apart. Subsequent differences, like cleavage patterns and coelom formation, are also established in these early embryonic stages.
8. What is the evolutionary advantage of indeterminate cleavage as seen in deuterostomes?
The main advantage of indeterminate cleavage is developmental flexibility. Because the early cells are not pre-destined for a specific function, the embryo can compensate for the loss of a cell without fatal defects. This adaptability is also what makes the formation of identical twins possible in humans and other deuterostomes, as an early embryo splitting into two can result in two complete, viable organisms.
