A nematode is an unsegmented worm from the phylum Nematoda. They are also known as roundworms, and can be used as model organisms in research eg. C. elegans due to their short life span, being easy and cheap to keep in a lab, and being transparent meaning that their internal structures van be easily visualised. Their genetics are also more similar to ours than unicellular organisms, making them more accurate models for human genetics than bacteria or yeast (which are also commonly used). Some nematodes are parasites affecting humans, other animals and plants.