Gills are pouch-like in:

Options

A. Pisces
B. Amphibia
C. Cyclostomes
D. All of these

Answer

**Step-by-Step Solution:**

1. **Understanding Gills**: Gills are specialized respiratory structures that allow aquatic animals to extract oxygen from water. They can be found in various forms across different classes of animals.

2. **Identifying Gills in Pouch-like Structures**: The question specifically asks about gills that are pouch-like. This indicates that we are looking for a class of animals where the gills are not fully developed or are structured in a way that resembles pouches.

3. **Examining Cyclostomes**: Cyclostomes are a group of jawless fish that include species like lampreys and hagfish. They belong to the superclass Agnatha. In these organisms, gills are indeed found in a pouch-like structure.

4. **Characteristics of Cyclostomes**: In cyclostomes, the gills are not fully formed like in other fish (Pisces). Instead, they are located in gill pouches, which have muscular walls and respiratory lamellae. This is a distinctive feature of cyclostomes.

5. **Conclusion**: Based on the characteristics of gills in different classes of animals, we conclude that gills are pouch-like in Cyclostomata, which is the correct answer.

**Final Answer**: Gills are pouch-like in Cyclostomata.

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