eelworm

/ˈilˌwɜrm/
noun
  1. A small, slender worm that lives in soil or water, often a parasite of plants or animals.
    • The farmer found eelworms damaging the roots of his potato crop.
    • Eelworms are so tiny that you need a microscope to see them clearly.
    • Some eelworms help break down dead plants in the soil.