A worm is an elongated, soft-bodied invertebrate. Some species of worms are so different from- even unrelated to- each other that they have not been classified under a single group. Distribution and habitat There are at least 1,000,000 kinds of worms. They are found almost all over the world. Worms are universal in distribution, occurring in marine, freshwater, and terrestrial habitats. Some worms that live in the ground help to condition the soil (e.g., annelids, aschelminths). Many thrive as parasites of plants (e.g., aschelminths) and animals, including humans (e.g., platyhelminths, aschelminths). Several other worms may be free-living, or nonparasitic. There are worms that live in freshwater, seawater, and even on the seashore. Ecologically, worms form an important link in the food chains in virtually all the ecosystems of the world. Classification In everyday language, the term worm is also applied to various