Which of the following is not the feature of a cartilaginous fish?

Options

A. Bilaterally flattened body
B. Absence of operculum
C. Copulatory organ present
D. Viviparity

Answer

To determine which of the following is not a feature of cartilaginous fish, we need to analyze each option provided in the question. Cartilaginous fish, such as sharks and rays, have distinct characteristics that differentiate them from bony fish.

### Step-by-Step Solution:

1. **Identify the Characteristics of Cartilaginous Fish**:
- Cartilaginous fish are primarily characterized by having a skeleton made of cartilage rather than bone.
- They possess a bilaterally symmetrical body structure.
- They lack an operculum, which is a bony flap covering the gills found in bony fish.
- Many cartilaginous fish have copulatory organs for reproduction.
- They exhibit various reproductive strategies, including oviparity (egg-laying) and viviparity (live-bearing), but they are not ovoviviparous.

2. **Analyze Each Option**:
- **Option 1: Bilaterally Flattened Body** - This is a feature of cartilaginous fish. They are indeed bilaterally symmetrical.
- **Option 2: Absence of Operculum** - This is also true for cartilaginous fish. They do not have an operculum.
- **Option 3: Copulatory Organ Production** - Cartilaginous fish do have copulatory organs, so this is a feature of them.
- **Option 4: Viviparity** - While some cartilaginous fish are viviparous, not all are, and this term can be misleading as it implies that all cartilaginous fish exhibit this reproductive method.

3. **Conclusion**:
- The correct answer is **Option 4: Viviparity**, as not all cartilaginous fish are viviparous, which makes it the feature that is not universally applicable to all cartilaginous fish.

### Final Answer:
**Option 4: Viviparity** is not a feature of all cartilaginous fish.