Which are primitive vertebrates?

Options

A. Amphioxus and Herdmania
B. Doliolum and Scoliodon
C. Balanoglossus and Salpa
D. Petromyzon and Myxine

Answer

**Step-by-Step Solution:**

1. **Understanding Vertebrates**: The question asks about primitive vertebrates. Vertebrates belong to the subphylum Vertebrata, which is part of the phylum Chordata.

2. **Divisions of Vertebrates**: Vertebrates can be divided into two main groups:
- **Agnatha**: These are jawless fishes, which are considered more primitive.
- **Gnathostomata**: These are jawed vertebrates, which include more advanced groups like bony fishes and tetrapods (amphibians, reptiles, birds, and mammals).

3. **Identifying Primitive Vertebrates**: Among the vertebrates, the most primitive are those in the Agnatha group, specifically known as cyclostomes. Cyclostomes are characterized by their circular mouths and lack of jaws.

4. **Examples of Primitive Vertebrates**: The two main examples of cyclostomes (primitive vertebrates) are:
- **Petromyzon** (lamprey)
- **Myxine** (hagfish)

5. **Exclusion of Other Options**: Other options presented in the question, such as amphioxus, chondrichthyes (cartilaginous fishes), balenoglossus, and salpa, do not belong to the primitive vertebrates category. Amphioxus is a cephalochordate, while the others are more advanced than the cyclostomes.

6. **Conclusion**: Therefore, the primitive vertebrates are the cyclostomes, specifically Petromyzon and Myxine.

**Final Answer**: The primitive vertebrates are the cyclostomes, specifically Petromyzon and Myxine.

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