What feature characterizes nematodes?

Nematodes are characterized primarily by their role as root-dwelling parasites in many agricultural systems. They are microscopic, unsegmented roundworms that can inhabit the soil and interact with plant roots, often leading to detrimental effects on plant health. Many plant-parasitic nematodes feed on root tissues, causing galls, lesions, or stunted growth, which can significantly impact crop yields.

In contrast, beneficial fungi enhance soil health and structure, improving nutrient availability and plant growth. Soil structure improvement is typically associated with various organisms, including earthworms and fungi, rather than nematodes. Additionally, pollinators such as bees and butterflies play a vital role in the reproduction of flowering plants, which is completely unrelated to nematodes and their functions. Thus, the defining characteristic of nematodes in this context is their role as parasites that specifically affect the roots of plants.