Understanding animal development is an important part of Biology. During embryonic development, animals follow different developmental pathways. Based on how the mouth and digestive system develop in the embryo, animals are divided into Protostomes and Deuterostomes.
This concept helps scientists understand the classification and evolution of animals.
What are Protostomes?
The word Protostome comes from Greek words:
- Proto = First
- Stoma = Mouth
So, Protostomes are animals in which the first opening formed during embryonic development becomes the mouth.
During early development:
- A fertilized egg divides repeatedly.
- A hollow ball of cells forms.
- An opening called the blastopore appears.
- In protostomes, this blastopore develops into the mouth.
The anus develops later.
Simple Definition:
Protostomes are animals whose embryonic blastopore develops into the mouth.
Characteristics of Protostomes
1. Mouth Develops First
- Blastopore forms the mouth.
2. Spiral Cleavage
- Cells divide in a spiral arrangement.
3. Determinate Cleavage
- Early embryonic cells have fixed developmental fate.
4. Coelom Formation by Splitting
- Body cavity forms through schizocoely.
5. Highly Diverse Group
- Includes many common animals.
Examples of Protostomes
Phylum Mollusca
Examples:
- Snail
- Octopus
- Oyster
Phylum Annelida
Examples:
- Earthworm
- Leech
Phylum Arthropoda
Examples:
- Cockroach
- Butterfly
- Crab
- Spider
Embryonic Development in Protostomes
Step 1: Fertilization
Egg and sperm combine.
↓
Step 2: Cleavage
Cells divide rapidly.
↓
Step 3: Blastula Formation
A hollow embryo develops.
↓
Step 4: Gastrulation
Blastopore appears.
↓
Step 5:
Blastopore → Mouth
↓
Anus develops later.
Difference Between Protostomes and Deuterostomes
Protostomes and Deuterostomes differ mainly in embryonic development.
| Feature | Protostomes | Deuterostomes |
|---|---|---|
| Meaning | First opening becomes mouth | First opening becomes anus |
| Blastopore develops into | Mouth | Anus |
| Mouth formation | First | Second |
| Cleavage type | Spiral cleavage | Radial cleavage |
| Cell fate | Determinate | Indeterminate |
| Coelom formation | Schizocoely | Enterocoely |
| Development flexibility | Less | More |
| Examples | Earthworm, insects, snails | Humans, starfish, fishes |
What are Deuterostomes?
The word Deuterostome means:
- Deutero = Second
- Stoma = Mouth
These are animals where the blastopore becomes the anus first, and the mouth develops later.
Examples:
- Starfish
- Fish
- Frog
- Birds
- Humans
Easy Trick to Remember
Protostomes
PROTO → PRIMARY → Mouth first
Deuterostomes
DEUTERO → SECOND → Mouth later
Why is this Classification Important?
Helps in:
- Understanding animal evolution
- Studying embryonic development
- Biological classification
- Comparing body organization
Scientists use this distinction to trace evolutionary relationships among animals.
NCERT Style Key Points
- Protostomes develop mouth from blastopore.
- Deuterostomes develop anus from blastopore.
- Protostomes show spiral and determinate cleavage.
- Deuterostomes show radial and indeterminate cleavage.
- Humans belong to deuterostomes.
Frequently Asked Questions (FAQs)
What is blastopore?
Blastopore is the first opening formed during embryonic development.
Are humans protostomes?
No. Humans are deuterostomes.
Which animals are protostomes?
Earthworms, insects, molluscs, and arthropods.
Why are protostomes called “mouth first” animals?
Because the blastopore develops into the mouth.
Practice Questions
Very Short Answer Questions
- What does protostome mean?
Answer: Mouth develops first. - Which opening becomes the mouth in protostomes?
Answer: Blastopore. - Name one protostome animal.
Answer: Earthworm. - Humans belong to which group?
Answer: Deuterostomes.
Fill in the Blanks
- Protostomes show ______ cleavage.
Answer: Spiral - In deuterostomes, blastopore forms the ______.
Answer: Anus - Coelom formation in protostomes is called ______.
Answer: Schizocoely
MCQs
1. In protostomes, blastopore becomes:
A. Eye
B. Mouth
C. Heart
D. Brain
Answer: B
2. Humans belong to:
A. Protostomes
B. Deuterostomes
C. Mollusca
D. Arthropoda
Answer: B
3. Protostomes show:
A. Radial cleavage
B. Spiral cleavage
C. No cleavage
D. Binary fission
Answer: B
4. Which is a protostome?
A. Starfish
B. Human
C. Earthworm
D. Fish
Answer: C
5. Coelom formation in protostomes occurs through:
A. Enterocoely
B. Schizocoely
C. Budding
D. Fragmentation
Answer: B
Final Summary
Protostomes and deuterostomes are major animal groups classified based on embryonic development. In protostomes, the mouth forms first from the blastopore, while in deuterostomes the anus forms first. This distinction is important in understanding evolution and biological classification.
Remember:
Protostomes → Mouth First
Deuterostomes → Mouth Later
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