What are nematodes?

Nematodes are microscopic, slender roundworms that are commonly found in a variety of environments, including soil, freshwater, and marine ecosystems. They play significant roles in the ecosystem as decomposers and can also be important in soil health, as they help to break down organic matter and recycle nutrients. Some species of nematodes are beneficial to plants, while others can be plant parasites, impacting crop yield and health. Their small size means they often go unnoticed, yet they are an integral part of the soil food web.

The other options refer to unrelated organisms. Colorful insects can exist in soil but are not the same as nematodes. Predatory fish inhabit aquatic environments, which is outside the scope of what nematodes are. Large mammals may affect crop yields but are also distinct from the roundworm classification, emphasizing the importance of recognizing the biological differences among these organisms.