Which of the following is/are not the characteristics of the Class Osteichthyes?
(i) Body is streamlined and mouth is terminal.
(ii) Gills are convered by operculum.
(iii) Skin convered with cycloid and placoid scales.
(iv) Many of them are viviparous.

Options

A. (iv) only
B. (iii) and (iv)
C. (i), (iii) and (iv)
D. (i) and (ii)

Explanation

To determine which of the given statements are not characteristics of the Class Osteichthyes (bony fishes), we will analyze each statement one by one.

1. **Statement (i): Body is streamlined and mouth is terminal.**
- **Analysis:** Bony fishes typically have a streamlined body shape that aids in swimming, and their mouths are usually located at the anterior end (terminal).
- **Conclusion:** This statement is a characteristic of Osteichthyes.

2. **Statement (ii): Gills are covered by operculum.**
- **Analysis:** In bony fishes, the gills are indeed covered by a bony flap known as the operculum, which protects the gills and aids in respiration.
- **Conclusion:** This statement is a characteristic of Osteichthyes.

3. **Statement (iii): Skin covered with cycloid and placoid scales.**
- **Analysis:** Bony fishes are primarily covered with cycloid or ctenoid scales. Placoid scales are characteristic of cartilaginous fishes (like sharks and rays), not bony fishes.
- **Conclusion:** This statement is NOT a characteristic of Osteichthyes.

4. **Statement (iv): Many of them are viviparous.**
- **Analysis:** Most bony fishes are oviparous, meaning they reproduce by laying eggs. While there are some exceptions where certain species are viviparous (giving birth to live young), this is not a common characteristic of the class as a whole.
- **Conclusion:** This statement is NOT a characteristic of Osteichthyes.

### Final Answer:
The statements that are NOT characteristics of the Class Osteichthyes are:
- (iii) Skin covered with cycloid and placoid scales.
- (iv) Many of them are viviparous.