Which of the following statements about nematodes is true?

Nematodes are classified as small roundworms, which is precisely what makes the answer accurate. These microscopic organisms belong to the phylum Nematoda and are found in various environments, including soil, freshwater, and marine settings. They play crucial roles in ecosystems, including nutrient cycling and as part of the food web.

The other statements do not correctly describe nematodes. While they may affect crops as pests, they are not insects, which belong to a different class of animals. Although some nematodes are parasitic, they are not defined as large parasites; in fact, many are quite small. Additionally, while some nematodes may thrive in aquatic environments, they are not exclusively aquatic animals, as many live in soil or even in plant tissues. Thus, the characterization of nematodes as small roundworms is both accurate and highlights their biological classification.