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
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the blastopore Develops into an anal
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The mouth in deuterostomes is formed by the gut that tunnels to the embryo
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Deuterostomes are Always enterococcus.
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The nervous system of deuterostomes is composed of the hollow nerve cord
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the body Composition is more complex as compared to protostomes
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During the development phase, they go through the intermediate tree cleavage where all the Blastoma can develop into the embryos completely
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Here, the animals undergo Radical cleavage
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deuterostomes contain fewer phyla and species as compared to protostomes
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echinoderms, hemichordates and chordates are Included in deuterostomes
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For deuterostomes, Early stages of embryo formation, archenteron development takes place.
Characteristics of Protostomes
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The blastopore develops into a mouth and not the anus
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Bigot tunnels into an embryo and forms the anus
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The Nervous System of protostomes is solid and has a ventral solid COD
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Organisms of protostomes undergo determinate cleavage.
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The blastopore produced in the development stages of the embryo cannot develop.
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Spiral cleavage is exhibited by protostomes
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Protostomes are Less evolved and more Complex than deuterostomes
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There is No archenteron development
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The anus arises at a secondary position
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Organisms of protostomes include flatworms annelids and Arthropods
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protostomes have multi ciliated cells
Subject Difficulty Level
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Biology is a comparatively difficult subject than the other sections of science, due to its complexity and diversity in concepts.
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However, with firm dedication and determination, all the topics can be easily tackled.
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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
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Relatively more marks can be scored through Biology subject if studied thoroughly
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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.
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The most important tip in learning Biology is to make notes.
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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.
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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
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deuterostomes and protostomes are two groups of coelomates
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deuterostomes And protostomes are differentiated based on their formation and cleavage during the development phase
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The distinction between deuterostomes and protostomes is that in deuterostomes blastopores develop into anal opening and in protostomes, blastopores develop into a mouth
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protosomes are invertebrates whereas deuterostomes Have chordates
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In protostomes, the mouth forms before the anus
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whereas in deuterostomes the anus is formed before the formation of the mouth
Samples Questions for Exam
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What are deuterostomes explain their properties?
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What are protostomes and explain their properties?
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Differentiate between deuterostomes and protostomes.
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What are the characteristics of deuterostomes?
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Advantages of being deuterostomes over protostomes.
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