The roundworm's scientific name is "nematode." Roundworms are tiny and abundant creatures, with more than 15,000 known species, according to the University of California Museum of Paleontology. About 90,000 nematodes have been found in a single decaying apple. Roundworms are found worldwide in all types of habitats.
"Nematode" is derived from a Greek word meaning "thread." The organism earned its name because of its worm-like slender shape. Compared to other animals, nematodes have a simple structure, according to Animal Diversity. Their skin does not have individual cells with nuclei but is a continuous mass with no differentiation. The skin produces a tough cuticle that takes the place of a skeleton. Long muscles under the skin allow the nematode to move by bending side to side. Roundworms have a few sensory organs and simple digestive systems.