Choose the false statement regarding Petromyzon.

Options

A. The circulatory system is closed
B. The body is devoid of scales
C. Mouth is circular and lacks jaws
D. It migrates to the ocean for spawing

Answer

To determine the false statement regarding Petromyzon (Lamprey), we can analyze the provided information step by step.

### Step-by-Step Solution:

1. **Classification**: Petromyzon is classified under the phylum Chordata and is known as Lamprey. This statement is true as Lampreys belong to the class Agnatha, which is characterized by the absence of jaws.

**Hint**: Remember that Lampreys are jawless fish and belong to the Chordata phylum.

2. **Mouth Structure**: The mouth of Petromyzon is described as full rounded or circular and lacks jaws. This is also true, as Lampreys have a sucker-like mouth that is circular in shape.

**Hint**: Focus on the unique mouth structure of Lampreys, which is adapted for their feeding habits.

3. **Circulatory System**: It is stated that the circulatory system of Petromyzon is closed. This is correct, as Lampreys have a closed circulatory system, which is typical of vertebrates.

**Hint**: Recall the difference between open and closed circulatory systems in animals.

4. **Body Scales**: The statement that the body is devoid of scales is accurate. Lampreys do not have scales, which distinguishes them from many other fish species.

**Hint**: Think about the physical characteristics that differentiate Lampreys from other fish.

5. **Migration for Spawning**: The statement that Petromyzon migrates to the ocean for spawning is false. Lampreys actually migrate to freshwater for spawning. After spawning, they typically die, which is a crucial part of their life cycle.

**Hint**: Consider the reproductive habits of Lampreys and where they choose to spawn.

### Conclusion:
The false statement regarding Petromyzon is that it migrates to the ocean for spawning; instead, it migrates to freshwater.