In invertebrates, the body temperature varies according to the external conditions. So they are called_______ animals.

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks for the term used to describe invertebrates whose body temperature varies with external conditions.

2. **Identifying the Characteristics of Invertebrates**: Invertebrates are animals without a backbone. They include various species such as insects, mollusks, and crustaceans. One key characteristic of many invertebrates is that their body temperature is influenced by the surrounding environment.

3. **Defining the Term**: Animals whose body temperature changes according to the external environment are referred to as "cold-blooded" animals. This means that their internal body temperature fluctuates with the temperature of their surroundings.

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