Choose the correct statement.

Options

A. All Pisces have gills covered by an operculum.
B. All mammals are viviparous.
C. All cyclostomes do not possess jaws and paired fins.
D. All reptiles have a three-chambered heart.

Answer

To solve the question "Choose the correct statement," we need to evaluate each of the provided options one by one:

### Step-by-Step Solution:

1. **Evaluate Option 1: "All Pisces have gills covered by an operculum."**
- Pisces, or fish, are divided into two main groups: bony fishes (Osteichthyes) and cartilaginous fishes (Chondrichthyes).
- Bony fishes have gills that are covered by an operculum, which is a bony flap.
- However, cartilaginous fishes, like sharks and rays, do not have an operculum; their gills are exposed.
- **Conclusion:** This statement is incorrect.

2. **Evaluate Option 2: "All mammals are viviparous."**
- Most mammals are indeed viviparous, meaning they give birth to live young.
- However, there is an exception: the monotreme known as the platypus, which lays eggs (oviparous).
- **Conclusion:** This statement is also incorrect.

3. **Evaluate Option 3: "All cyclostomes do not possess jaws and beard fins."**
- Cyclostomes, which include lampreys and hagfish, are characterized by the absence of jaws.
- They also lack paired fins, which are typical in other vertebrates.
- **Conclusion:** This statement is correct.

4. **Evaluate Option 4: "All reptiles have a three-chambered heart."**
- Most reptiles do have a three-chambered heart, but there is an exception: crocodilians, which have a four-chambered heart.
- **Conclusion:** This statement is incorrect.

### Final Answer:
The correct statement is **Option 3: "All cyclostomes do not possess jaws and beard fins."**

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