Which of the following statements is not true for Agnatha members?

Options

A. They include hag fishes and lampreys
B. They have notochord throughout their lives
C. They are known as cyclostomes
D. They have bony skeletons

Answer

To determine which statement is not true for Agnatha members, we will analyze each option provided.

### Step-by-Step Solution:

1. **Understanding Agnatha**:
- Agnatha is a division of vertebrates that are characterized by the absence of jaws. This group includes organisms such as hagfishes and lampreys.

2. **Analyzing the Statements**:
- **Statement A**: "They include hagfishes and lampreys."
- This statement is true. Both hagfishes and lampreys are indeed members of the Agnatha group.

- **Statement B**: "They have notochord throughout their lives."
- This statement is also true. Members of Agnatha retain a notochord throughout their lives, even though in some vertebrates it may be replaced by a vertebral column.

- **Statement C**: "They are known as cyclostomes."
- This statement is true as well. The class Cyclostomata, which includes hagfishes and lampreys, is commonly referred to as cyclostomes.

- **Statement D**: "They have bony skeletons."
- This statement is false. Agnatha members do not have bony skeletons; instead, their skeletal structures, including the vertebral column and cranium, are made of cartilage.

3. **Conclusion**:
- The statement that is not true for Agnatha members is **Statement D**: "They have bony skeletons."

### Final Answer:
- The correct answer is **Statement D**.