Which organisms are generally microscopic unsegmented roundworms that live in moist soil, water, or decaying matter or as parasites?

• A. Nematodes
• B. Bacteria
• C. Protozoa
• D. Earthworms

Answer: (A)

Nematodes are microscopic, unsegmented roundworms that live in moist soil, water, or decaying matter and can also be parasites. This description fits nematodes precisely: they have an elongated, cylindrical body with no true body segments, and many are so small you need a microscope to see them. In turf and soil contexts, they’re noted for their roles in nutrient cycling and for some species that parasitize plants or animals.

Bacteria are tiny single-celled organisms without a worm-like shape. Protozoa are also single-celled organisms and typically aren’t described as wormlike or unsegmented roundworms. Earthworms are larger, visible to the naked eye, and are segmented worms belonging to a different group (annelids).