Nematodes – A type of invertebrate animal with soft, unsegmented, thread-like bodies

(Pronounced neh-muh-tohd)

Note: Best examples of nematodes are roundworms.

Note: Earthworms and roundworms while both classified as "worms" are fundamentally different. Earthworms are segmented worms belonging to the phylum annelida, while roundworms are non-segmented worms of the phylum nematoda.

To remember the meaning of nematode, associate nematode with roundworm and use that mnemonic to remember nematodes are soft, unsegmented, thread-like bodies. Use the following mnemonic:

Never annoy a mother toad (nematode) surrounded by worms (roundworm).

Nematodes, also known as roundworms, are a large phylum of simple invertebrate animals with long, cylindrical, unsegmented bodies that taper at both ends. They have a tough outer covering that protects their body that must shed as they grow. Unlike more complex animals, nematodes have a simple body plan with a straight digestive system that runs from mouth to anus, and they lack circulatory and respiratory systems, instead relying on diffusion for gas exchange and nutrient transport. They move by contracting longitudinal muscles in a characteristic thrashing motion.

Nematodes are incredibly abundant and diverse, found in virtually every environment including soil, freshwater, marine environments, and as parasites inside plants and animals, including humans.