Constituting the Superphylum category of animals, Deuterostomes are the sister classification to the Protosomia clade and forms the Nephrozoa clade (similar descendants from a common ancestor). However, there are notable differences between a Deuterostome and a Protosome. 

We are going to learn about the same along with the definition, examples and important characteristic to the Deuterostome. Let us start by reading about what is a Deuterostome and its references. 

The Basic Definition of a Deuterostome

The word “Deuterostome” means ‘2nd mouth’. Now, it is understood that Deuterostomes are a Superphylum from the Animalia Kingdom that is well-know for its blastopore and bilateral symmetry. Blastopore is the first-developed opening-kind cleavage and it generates up the anus in the development of an embryo. 

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A few Important Characteristics of a Deuterostome

The major characteristic of a Deuterostome lies in its Radial Cleavage Property. Each of the 4 zygotic cells undergoes perpendicular and parallel division from its original axis in symmetrical paths. The fate of each embryonic cell is not predictable beforehand and thus, the change of location in its positioning influences in alterations at the early embryogenesis phase. 

The endodermal layer is formed at the blastula’s small indentation called the blastopore. The opposite direction of this blastopore is developed into the mouth and the first cavity gets the structure of the anus. From the primitive gut of the Deuterostome is defined by its internal and minute outgrowths, gets fused and forms the coelom. This step is called the Enterocoelom of the Gastrula phase. The coelomic activity then begins after its pouches undergo complete fusion. 

  • The Peripheral cells of the Gastrula will form the Ectoderm, in the case of egg-laying deuterostomes. This gets converted into hair, nervous system and the skin. The layer between Endoderm and Ectoderm is the Mesoderm that helps in the formation of the skeletal system, blood, kidneys, heart, and other important connective tissues of the body.

  • The blastocyst which is similar to the blastula creates the placenta for the embryo and 3 primary germinal cells are formed from the inner cells, in the case of human beings and mammals. 

The Major Classification of Deuterostomes with Examples

The clades of Deuterostome are divided into 3 main categories as present in the following:

  1. Hemichordata - The lower or Middle Cambrin Deuterostome that includes Acorn worms, graptolites, etc.

  1. Chordata - Which includes the kin of all known living vertebrates including fishes, reptiles and birds. Here, the vertebral column or spinal cord is replaced with a structure called the Notochord.

  1. Echinodermata - The phylum for marine animals such as sea cucumbers, starfishes, brittle stars, sea urchins, etc. identified with its radial symmetry. 

Deuterostomes and Protostomes Difference

Following pointers are some of the major contrasting features between a Deuterstome and a Protosome. However, note that all the Deuterstomes is still the sister for the clade Protosomes in general.

  • The cleavage of a zygote in Deuterostome is indeterminate and radial, while it is determinate and spiral in a Protosome. 

  • The nervous system in a protosome is ventral and solid but observed with pharyngeal gill slits with a hollow nerve cord as in the case of  Deuterostome. 

  • Schizocoelous is a mass collection of solid cells that help in the splitting up of the mesoderm to create the coelom. This is seen in the case of a Protosome. On the flip side, Deuterostomes follow the step called Enterocoelous, where the folding of the archenteron leads to the generation of a coelom.

  • In Deuetrosomes, there is the presence of only 1 cilium for each cell. Whereas, a  Protosome posses Multiciliated Larval ciliary cells or bands.

  • The Blastospore forms into the anus in Deuterostome but turns into the mouth for a Protosome. 

FAQ (Frequently Asked Questions)

1. State any 1 similarity between Protosomes and Deuterostomes.

The formation of an embryo as a hollow ball-like cell structure is the first and common step in both Protosomes and Deuterostomes.

2. Why is the ancestral pattern of an Echinoderm difficult to study?

It is difficult to study and evaluate the ancestral pattern of an Echinoderm due to its formation of a highly complex and modified nervous system.

3. Name the oldest Deuterstome found in the history of evolution.

‘Saccorhytus coronarius’ is the oldest ever-known Deuterostome that was estimated to have lived around 540 million years before. The research scholars and archaeologists who identified this Deuterostome believe that the Saccorhytus might be the common ancestor to all the Deuterostomes known-previously.

4. What are the 6 taxonomic classes under Echinodermata?

The 6 taxonomic classes under Echinodermata include Asteroidea, Echinoidea, Crinoidea, Holothuroidea & Concentricycloidea and Ophiuroidea.

5. Give the 3 major classification subtypes for the Chordates.

The Chordates can be classified into the 3 major subtypes and they are namely Urochordata, Vertebrata, and the Cephalochordata. Note that, all the vertebrates are chordates but not all the known chordates can be vertebrates.