Choose the correct difference from the following

Options

A. `{:("Pristis",,"Catla"),("3-chambered heart",-,"2- chambered heart"):}`
B. `{:("Pristis",,"Catla"),("Small placoid scales",-,"Large placoid scales"):}`
C. `{:("Pristis",,"Catla"),("Ventral mouth",-,"Terminal mouth"):}`
D. `{:("Pristis",,"Catla"),("Swim bladder present",-,"Swim bladder absent"):}`

Answer

To solve the question regarding the differences between Pristis (sawfish) and Catla (a type of bony fish), we will analyze the characteristics of both groups: Chondrichthyes (cartilaginous fishes) and Osteichthyes (bony fishes).

### Step-by-Step Solution:

1. **Identify the Groups**:
- Pristis (sawfish) belongs to the class **Chondrichthyes**, which are characterized by having a skeleton made of cartilage.
- Catla belongs to the class **Osteichthyes**, which are bony fishes characterized by having a skeleton made of bone.

**Hint**: Remember the classification of fishes based on their skeletal structure.

2. **Heart Structure**:
- Both Chondrichthyes and Osteichthyes have a **two-chambered heart** consisting of one atrium and one ventricle. Therefore, the statement claiming a three-chambered heart for either group is incorrect.

**Hint**: Recall that the heart structure in fishes is generally two-chambered.

3. **Scale Types**:
- Chondrichthyes, including Pristis, have **placoid scales**.
- Osteichthyes, such as Catla, have **cycloid or ctenoid scales**. The statement that Pristis has small placoid scales while Catla has large placoid scales is incorrect.

**Hint**: Differentiate between the types of scales found in cartilaginous and bony fishes.

4. **Mouth Position**:
- Pristis has a **ventral mouth**, which is located on the underside of its body.
- Catla has a **terminal mouth**, which is located at the front of its body. This statement is correct.

**Hint**: Observe the anatomical features of the fishes to determine mouth positions.

5. **Swim Bladder**:
- Chondrichthyes (like Pristis) do not have a swim bladder. They rely on constant swimming to maintain buoyancy.
- Osteichthyes (like Catla) possess a swim bladder that helps them maintain buoyancy. The statement regarding the presence of a swim bladder is incorrect for Pristis.

**Hint**: Understand the role of the swim bladder in bony fishes versus the adaptations of cartilaginous fishes.

### Conclusion:
After analyzing the statements, the only correct difference is that Pristis has a ventral mouth while Catla has a terminal mouth. Therefore, the correct answer is:

**Option 3: Pristis has a ventral mouth; Catla has a terminal mouth.**