In animals, specialized cells for osmoregulation and excretion was first seen in

Options

A. Annelida
B. Coelenterata
C. Mollusca
D. Platyhelminthes

Answer

To solve the question "In animals, specialized cells for osmoregulation and excretion was first seen in," we can follow these steps:

### Step-by-Step Solution:

1. **Understanding the Question**: The question asks about specialized cells responsible for osmoregulation and excretion in animals. We need to identify which group of animals first developed these specialized cells.

2. **Identifying Specialized Cells**: The specialized cells that perform osmoregulation and excretion in certain animals are known as **flame cells**. These cells play a crucial role in maintaining the balance of water and salts in the organism.

3. **Function of Flame Cells**: Flame cells are part of a structure called **protonephridia**. Protonephridia consist of flame cells and excretory tubules. The flame cells are responsible for ultrafiltration, similar to the function of kidneys in higher organisms, while the excretory tubules act like a bladder.

4. **Organisms with Flame Cells**: Flame cells are primarily found in **flatworms**, which belong to the phylum **Platyhelminthes**. This group of organisms is known for having these specialized cells for excretion and osmoregulation.

5. **Evaluating Other Options**:
- **Annelids** have nephridia, which are more complex structures for excretion.
- **Cnidarians** (like jellyfish) do not have specialized organs for excretion.
- **Mollusks** also possess nephridia for excretion.

6. **Conclusion**: Since flame cells and protonephridia are first seen in flatworms (Platyhelminthes), we conclude that the correct answer to the question is **Platyhelminthes**.

### Final Answer:
The specialized cells for osmoregulation and excretion were first seen in **Platyhelminthes**.

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