Scales in cartilaginous fishes are

Options

A. (a) cycloid
B. (b) Ctenoid
C. (c) Placoid
D. (d) Leptoid

Answer

### Step-by-Step Solution:

1. **Identify the Types of Fishes**:
- There are two main types of fishes: cartilaginous fishes and bony fishes.
- Cartilaginous fishes are scientifically known as **Chondrichthyes**.
- Bony fishes are referred to as **Osteichthyes**.

2. **Understand the Skeleton Composition**:
- Cartilaginous fishes have a skeleton made of **cartilage**.
- Bony fishes have a skeleton made of **bones**.

3. **Examples of Each Type**:
- Examples of cartilaginous fishes include **sharks** and **rays**.
- Examples of bony fishes include **clownfish**, **tuna**, and **catfish**.

4. **Function of Scales**:
- Scales serve as a protective covering for fishes, providing defense against predators and physical damage.

5. **Types of Scales**:
- In cartilaginous fishes, the scales are known as **placoid scales**.
- Placoid scales have a structure similar to teeth and are covered with **enamel**.
- In contrast, bony fishes have scales classified as **leptoid scales**, which can be further divided into **cycloid** and **ctenoid** scales.

6. **Conclusion**:
- The correct answer to the question about the type of scales in cartilaginous fishes is **placoid scales**.

### Final Answer:
- The scales in cartilaginous fishes are **placoid scales**.

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