Assertion: Herbivores are also called as key industry animals because they convert plant matter into animal matter.
Reason: Decomposers play a pivotal role in the ecosystem and they indirectly support the producers.

Explanation

### Step-by-Step Solution:

1. **Understanding the Assertion**:
- The assertion states that herbivores are referred to as key industry animals because they convert plant matter into animal matter.
- This is true because herbivores (primary consumers) feed on plants (producers) and in doing so, they transform the energy stored in plant matter into animal matter.

2. **Understanding the Reason**:
- The reason provided is that decomposers play a pivotal role in the ecosystem and indirectly support the producers.
- This is also true. Decomposers break down dead organic matter, returning nutrients to the soil, which supports plant growth (producers).

3. **Analyzing the Relationship**:
- While both the assertion and reason are correct, they address different aspects of the ecosystem.
- The assertion focuses on the role of herbivores in converting plant matter to animal matter, while the reason discusses the role of decomposers in nutrient cycling.

4. **Conclusion**:
- Since both statements are true but the reason does not explain the assertion, the correct answer is that both the assertion and reason are true, but the reason is not the correct explanation of the assertion.

### Final Answer:
- Both assertion and reason are true, but reason is not the correct explanation of the assertion.