The class of vertebrates which has exclusively aquatic habitat is________.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the class of vertebrates that lives exclusively in aquatic habitats. This means we are looking for a group of animals that are fully adapted to life in water.

2. **Identifying Vertebrate Classes**: Vertebrates are categorized into different classes, including mammals, birds, reptiles, amphibians, and fishes. Among these, we need to determine which class is entirely aquatic.

3. **Focusing on Fishes**: The class that is exclusively aquatic is the class of fishes. Fishes are adapted to living in water and have various features that make them suitable for an aquatic environment.

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