Teeth in chondrichthyes are modified

Options

A. Placoid scales
B. Cycloid scales
C. Ctenoid scales
D. Ganoid scales

Answer

### Step-by-Step Solution

1. **Understanding Chondrichthyes**:
- Chondrichthyes is a class of cartilaginous fishes, which includes species like sharks and rays. They are part of the subphylum Vertebrata and the phylum Chordata.

2. **Characteristics of Chondrichthyes**:
- Members of this class have a cartilaginous endoskeleton instead of a bony skeleton. They are primarily marine animals and have streamlined bodies for efficient swimming.

3. **Skin Structure**:
- The skin of Chondrichthyes is tough and contains minute scales. These scales are known as placoid scales, which are similar in structure to teeth.

4. **Teeth Modification**:
- The teeth of Chondrichthyes are not ordinary teeth; they are modified placoid scales. This means that the structure of the teeth is derived from the same material as their skin scales.

5. **Direction of Teeth**:
- The teeth in Chondrichthyes are typically backwardly directed, which helps them grip and hold onto their prey effectively.

6. **Examples of Chondrichthyes**:
- Common examples include the dogfish (Scoliodon), sawfish, great white shark, and stingray. These examples illustrate the diversity within this class.

7. **Final Answer**:
- Therefore, the correct answer to the question "Teeth in Chondrichthyes are modified" is that they are modified placoid scales.