Which of the following is not correct for petromyzon ?

Options

A. Ectoparasite on fish gills
B. 6-15 pairs of gill-slits
C. Open circulatory system
D. Jaws absent

Answer

To determine which statement about Petromyzon is not correct, we will analyze the provided options step by step.

### Step 1: Identify the characteristics of Petromyzon
Petromyzon, commonly known as lampreys, belong to the phylum Chordata. They possess several key features:
- Presence of a notochord and a nerve cord.
- During embryonic development, they exhibit 6-15 pairs of gill clefts.
- They are known to be ectoparasites on fish.

### Step 2: Evaluate the options
1. **Ectoparasites on fishes**: This statement is correct. Lampreys attach themselves to fish and feed on their blood and tissues.

2. **6-15 pairs of gill clefts are present**: This statement is also correct. Lampreys have multiple gill clefts which are characteristic of their developmental stage.

3. **Open circulatory system**: This statement is incorrect. Lampreys, being chordates, have a closed circulatory system, not an open one.

4. **Jaws are absent**: This statement is correct. Lampreys do not have jaws; instead, they have a round mouth with teeth.

### Step 3: Conclusion
Based on the evaluation of the options, the statement that is not correct for Petromyzon is "open circulatory system." Therefore, the answer is option C.