What are Deuterostomes? Complete Notes for Students

In Biology, animals are classified into different groups based on their body structure and embryonic development. One important classification is based on how the mouth and anus develop during early embryo formation.

Animals in which the first embryonic opening develops into the anus and the mouth develops later are called Deuterostomes.

Understanding deuterostomes helps students learn about animal evolution, embryology, and biological classification.

Meaning of Deuterostomes

The word Deuterostome comes from Greek words:

Deutero = Second
Stoma = Mouth

Thus, Deuterostomes means “mouth develops second.”

During embryonic development:

The embryo forms an opening called the blastopore.
In deuterostomes, the blastopore develops into the anus.
The mouth develops later at another location.

Simple Definition

Deuterostomes are animals in which the blastopore develops into the anus and the mouth forms later during embryonic development.

Characteristics of Deuterostomes

1. Anus Develops First

The blastopore forms the anus.
Mouth appears later.

2. Radial Cleavage

Cells divide in a symmetrical arrangement.
Each cell layer forms directly above another.

3. Indeterminate Cleavage

Early embryonic cells can still develop independently.
Removal of one cell may not stop complete development.

4. Coelom Formation by Enterocoely

Body cavity develops from outgrowths of the digestive tract.

5. Higher Developmental Flexibility

Cells remain capable of different developmental paths in early stages.

Also Read : What is Pericardium? Structure, Functions and Importance of Pericardium

Embryonic Development in Deuterostomes

Step 1: Fertilization

Sperm and egg combine.

↓

Step 2: Cleavage

Rapid cell division occurs.

↓

Step 3: Blastula Formation

Embryo becomes a hollow structure.

↓

Step 4: Gastrulation

Blastopore appears.

↓

Step 5:

Blastopore → Anus

↓

Mouth develops later.

Also Read : What is Protostomes? Difference Between Protostomes and Deuterostomes

Examples of Deuterostomes

Deuterostomes mainly include animals from these groups:

Phylum Echinodermata

Examples:

Starfish
Sea urchin
Sea cucumber

Phylum Chordata

Examples:

Fish
Frog
Reptiles
Birds
Humans

Why Humans are Deuterostomes

Humans belong to Phylum Chordata.

During human embryonic development:

Blastopore develops into the anus.
Mouth appears later.

Therefore, humans are classified as deuterostomes.

Deuterostomes vs Protostomes

Feature	Deuterostomes	Protostomes
Meaning	Mouth develops second	Mouth develops first
Blastopore forms	Anus	Mouth
Cleavage	Radial	Spiral
Cell fate	Indeterminate	Determinate
Coelom formation	Enterocoely	Schizocoely
Examples	Humans, fishes	Earthworm, insects

Importance of Studying Deuterostomes

Studying deuterostomes helps students understand:

Animal evolution
Embryonic development
Classification of organisms
Developmental biology
Relationship between different animal groups

Also Read : Chapter 1 some basic concepts of chemistry MCQ Practice Questions For JEE and NEET Exam : Level 0

Easy Trick to Remember

Deuterostomes

DEUTERO → SECOND → Mouth later

Protostomes

PROTO → FIRST → Mouth first

NCERT Style Key Points

Deuterostomes develop anus first.
Mouth forms later during development.
They show radial cleavage.
They have indeterminate cleavage.
Humans belong to deuterostomes.
Coelom formation occurs through enterocoely.

Frequently Asked Questions (FAQs)

What are deuterostomes?

Animals whose blastopore develops into the anus.

Are humans deuterostomes?

Yes, humans are deuterostomes.

What is blastopore?

The first opening formed during embryo development.

Which cleavage occurs in deuterostomes?

Radial cleavage.

Practice Questions

Very Short Answer Questions

What does deuterostome mean?
Answer: Mouth develops second.
What does blastopore become in deuterostomes?
Answer: Anus.
Name one deuterostome animal.
Answer: Starfish.
Which phylum includes humans?
Answer: Chordata.

Fill in the Blanks

In deuterostomes, blastopore forms the ______.
Answer: Anus
Deuterostomes show ______ cleavage.
Answer: Radial
Humans belong to phylum ______.
Answer: Chordata

MCQs

1. In deuterostomes, blastopore becomes:

A. Mouth
B. Eye
C. Anus
D. Heart

Answer: C

2. Which cleavage occurs in deuterostomes?

A. Spiral
B. Radial
C. Binary
D. Budding

Answer: B

3. Humans belong to:

A. Protostomes
B. Deuterostomes
C. Mollusca
D. Arthropoda

Answer: B

4. Coelom formation in deuterostomes occurs through:

A. Schizocoely
B. Enterocoely
C. Fragmentation
D. Budding

Answer: B

5. Which animal is a deuterostome?

A. Earthworm
B. Cockroach
C. Human
D. Snail

Answer: C

Final Summary

Deuterostomes are animals in which the blastopore develops into the anus and the mouth forms later. They show radial cleavage, indeterminate development, and enterocoelous coelom formation. Humans and many advanced animals belong to this group, making deuterostomes an important concept in Biology and evolution.