Which type of scales are found on the skin of cartilaginous fishes ?

Options

A. Ganoid
B. Placoid
C. Ctenoid
D. Cycloid

Answer

To answer the question regarding the type of scales found on the skin of cartilaginous fishes, we can follow these steps:

### Step-by-Step Solution:

1. **Identify the Group of Fishes**:
- Cartilaginous fishes belong to the class Chondrichthyes. This class includes sharks, rays, and skates.

2. **Understand the Structure of Cartilaginous Fishes**:
- Unlike bony fishes (Osteichthyes), cartilaginous fishes have an endoskeleton made of cartilage rather than bone.

3. **Examine the Types of Scales**:
- Fishes have different types of scales based on their classification. The main types of scales are:
- **Placoid Scales**: Found in cartilaginous fishes.
- **Cycloid Scales**: Found in bony fishes.
- **Ctenoid Scales**: Also found in bony fishes.
- **Ganoid Scales**: Present in some primitive bony fishes.

4. **Conclude the Type of Scales in Cartilaginous Fishes**:
- The specific type of scales that are present on the skin of cartilaginous fishes is called **placoid scales**. These scales are small, tooth-like structures that provide protection and reduce drag while swimming.

5. **Final Answer**:
- Therefore, the type of scales found on the skin of cartilaginous fishes is **placoid scales**.