Jaws are

Options

A. Absent in fishes
B. Absent in cyclostomes
C. Present in cyclostomes
D. Present in Myxine

Answer

### Step-by-Step Solution:

1. **Understanding Jaws in Chordates**: Jaws are specialized structures that are primarily found in certain groups of chordates. They are essential for feeding and are a significant evolutionary advancement.

2. **Subphylum Classification**: The phylum Chordata is divided into three subphyla:
- **Eurochordata**: These organisms have a notochord primarily in the tail region. An example is Ascidia.
- **Cephalochordata**: In these organisms, the notochord extends from head to tail.
- **Vertebrata**: This subphylum includes organisms with a backbone and is further divided into two classes based on the presence of jaws.

3. **Agnatha vs. Gnathostomata**:
- **Agnatha**: This class includes jawless organisms, such as cyclostomes (e.g., lampreys and hagfish). They have circular mouths made of muscle rather than jaws.
- **Gnathostomata**: This class includes organisms with jaws. Examples include amphibians, reptiles, mammals, and many fishes.

4. **Identifying the Presence or Absence of Jaws**:
- **Fishes**: Most fishes belong to the Gnathostomata class, meaning they possess jaws.
- **Cyclostomes**: These are jawless and belong to the Agnatha class, confirming that they do not have jaws.
- **Myxine**: This is a genus within the cyclostomes, which also confirms the absence of jaws.

5. **Conclusion**: Based on the classification and characteristics of these groups, jaws are absent in cyclostomes (Agnatha) and present in gnathostomes (which include most fishes).

### Final Answer:
Jaws are present in Gnathostomata (jawed vertebrates) and absent in Agnatha (jawless vertebrates such as cyclostomes).

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