Which of the following feature of bony fish is missing in cartilaginous fishes

Options

A. Operculum
B. Placoid scales
C. Poikilothermic
D. Paired fins

Answer

To solve the question "Which of the following feature of bony fish is missing in cartilaginous fishes?", we will analyze the options provided and identify the key differences between bony fish and cartilaginous fish.

### Step-by-Step Solution:

1. **Understanding the Types of Fish**:
- Bony fish (Osteichthyes) have a skeleton made of bone.
- Cartilaginous fish (Chondrichthyes) have a skeleton made of cartilage.

2. **Analyzing the Options**:
- **Option 1: Operculum**: This is a bony flap that covers and protects the gills in bony fish. Cartilaginous fish do not have an operculum; instead, they have exposed gill slits.
- **Option 2: Placoid Scales**: These are small, tooth-like structures found on the skin of cartilaginous fish such as sharks and rays. They are not a feature of bony fish, so this option is incorrect.
- **Option 3: Poikilothermic**: Both bony and cartilaginous fish are considered poikilothermic (cold-blooded), meaning their body temperature varies with the environment. This option does not differentiate between the two types of fish.
- **Option 4: Paired Fins**: Both bony and cartilaginous fish possess paired fins, so this option is also incorrect.

3. **Conclusion**:
- The only feature that is present in bony fish but missing in cartilaginous fish is the **Operculum**. Therefore, the correct answer is **Option 1**.

### Final Answer:
**The feature of bony fish that is missing in cartilaginous fishes is the Operculum.**

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