A worm is an elongated, soft-bodied invertebrate. Some species of worms are so different from—even unrelated to—each other that they're not classified under a single group. Distribution and habitat There are at least 1,000,000 species of worms. They are found almost all over the world. Worms are universal in distribution, occurring in marine, freshwater, and terrestrial habitats. Some worms living in the ground help to condition the soil (for example, annelids, aschelminths). Many… (More on Worm)