Deuterostomes- Definitions, Characteristics and Examples

All human beings have a single mouth. However, there are organisms in the world that have a second mouth. Deuterostomes are a group of animals that belong to the kingdom Animalia which has a second mouth.

Table of Contents:

What are Deuterostomes?
Characteristics of Deuterostomes
Examples of Deuterostomes
Difference between Protostome and Deuterostome
Practice Problems
Frequently Asked Questions

What are Deuterostomes?

Deuterostomes is a word that refers to the second mouth. A deuterostome is a group of animals that are bilaterally symmetrical and has a blastopore, the first opening in the cleavage, which develops into an anus by the time of embryonic development. They include animals Echinodermata, Hemichordata and Chordata, like sea squirts, urchins, starfish and lancelets.

Characteristics of Deuterostomes

Blastopore is where the anus develops from the first cavity and is then followed by the mouth formation on the other side. It migrates to the other end forming the endodermal layer.
The four cells of the zygote get a perpendicular and parallel division symmetrically to the axis of the original body.
The embryonic cell is indeterminate as it gets altered when they are moved out during embryonic development. If they are isolated, each cell has the capability to develop into a complete embryo.
The formation of coelom starts at the stage of gastrula development. They are formed by the fusion of internal outgrowths. The protrusion membrane comes out to form a mesodermal layer between the ectoderm and endoderm. These enterocoelom pouches combine together to form a coelomic cavity.
The blastocyst in mammals forms the placenta. The inner cells emerge into three germinal layers.
The ectoderm is formed as the nervous system, skin and hair in deuterostomes which lay eggs. On the other hand, the mesoderm forms as muscle, kidney, blood, skeletal systems and heart for them.

Examples of Deuterostomes

Phylum Echinodermata

Phylum Echinodermata has mostly marine animals which have spiny skin and bilateral symmetry. The adult species may have radial symmetry. It includes a different variety of about seven thousand species of marine animals. There are no freshwater or terrestrial echinoderms discovered yet. Some of the common examples of echinoderms include:

Starfish
Sea urchins
Sea lily
Sea cucumber
Sand dollars

Phylum Chordata

The presence of notochord characterises phylum Chordata. The notochord is replaced by a vertebral column. They have pharyngeal slits and dorsal hollow nerve cords. Phylum Chordata is classified into three subdivisions: Urochordata, Cephalochordata and Vertebrata. Some of the common features of Chordates in different life stages are:

Notochord is a rod-like structure that supports the nerve cord. It is later replaced by a vertebral column.
Dorsal Nerve Cord is a nerve fibre that connects the brain to other parts of the body.
The post-anal tail is an extension beyond the anus that helps in the locomotion of the body.
Pharyngeal Slits are openings that connect the mouth and throat and allow water entry through the mouth.

Some examples of Phylum Chordata are fishes, reptiles, amphibians, birds and mammals.

Difference between Protostome and Deuterostome

In some cases, Protostomia and Deuterostome are identified as the same. They are completely different. Here are some of the differences between Protostome and Deuterostome listed below:

Protostome	Deuterostome
Blastopore develops as a mouth.	Blastopore develops as an anus.
The cleavage of a zygote is spiral and determinate.	The cleavage of the zygote is radial and indeterminate.
For the second opening, the embryo forms into the anus.	For the second opening, the embryo forms into the mouth.
The nervous system is formed by a solid ventral nerve cord.	They have pharyngeal gill slits and hollow nerve cords.
They are multi-ciliated cells	They are single cilium in each cell
Examples: Arthropods, flatworms and molluscs.	Example: Chordates and Echinodermata

Practice Problems

Q1. Which of the following is not an example of Deuterostome?

A. Chordates
B. Arthropods
C. Echinodermata
D. None of the above

Answer: B. Arthropods

Example: Arthropods are an example of Protostomes.

Q2. Which of the following helps in the locomotion of Deuterostome?

A. Pharyngeal Slits
B. Notochord
C. Post-Anal Tail
D. None of the above

Answer: C. Post-Anal Tail

Explanation: Post-Anal Tail is an extension beyond the anus that helps in the locomotion of the body.

Q3. Which of the following is developed as an anus in the Deuterostome?

A. Ectoderm
B. Blastopore
C. Coelom
D. None of the above

Answer: B. Blastopore

Explanation: Deuterostome has a blastopore, the first opening in the cleavage, which develops into an anus by the time of embryonic development.

Frequently Asked Questions

Q1. Are humans Deuterostomes?
Answer: Yes, humans come under Deuterostomes. We fall under the bilateral group, which is one of the characteristics of Deuterostomes. The organisms of Deuterostomes have bilateral symmetry, which means they have the same matching left and right sides to their bodies.

Q2. Which organ is not present in the Echinodermes?
Answer: In Echinodermes, the excretory organs are absent. As they don't have separate excretory tracts, all the waste diffuses through the respiratory tract in the form of ammonia.

Q3. Which is the oldest Deuterostome found?
Answer: Saccorhytus coronarius is the oldest Deuterostome discovered, which lived around 540 million years ago. It is believed that Saccorhytus coronarius might be the common ancestor of all Deuterostomes.