Which of the following classes is incorrectly matched with its general characters ?

Options

A. Cyclostomata : Lack jaws and paired fins and body is covered with placoid scales.
B. Osteichthyes : Four pair of gills are covered with an operculum and skin is covered with cycloid scales
C. Reptilla : Tympanum represents ear and fertilisation is internal
D. Aves : Endoskeleton is fully ossified and long bones are hollow with air cavities called as pneumatic bones.

Explanation

To solve the question "Which of the following classes is incorrectly matched with its general characters?", we will analyze each option provided in the question.

### Step-by-Step Solution:

1. **Option A: Class Cyclostomata**
- General Characters: Lacks jaws, paired fins, and bodies covered with placoid scales.
- Analysis: Cyclostomata includes jawless fish like hagfish and lampreys. They do not have jaws, paired fins, or scales. Therefore, this option is incorrectly matched.

2. **Option B: Class Osteichthyes**
- General Characters: Four pairs of gills, covered with operculum, skin covered with cycloid scales.
- Analysis: Osteichthyes, or bony fish, have these characteristics. They possess paired fins and are correctly matched.

3. **Option C: Class Reptilia**
- General Characters: Thickened body, scales over the body, internal fertilization.
- Analysis: Reptiles do have a thickened body covered with scales and exhibit internal fertilization. This option is correctly matched.

4. **Option D: Class Aves**
- General Characters: Hollow bones, pneumatic bones, fully ossified endoskeleton.
- Analysis: Birds (Aves) indeed have hollow bones to reduce weight for flight and a fully ossified endoskeleton. This option is also correctly matched.

### Conclusion:
The incorrectly matched class is **Option A: Class Cyclostomata**.

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