Nematodes

The nematodes are one of the most species-rich tribes of the animal kingdom. So far, more than 20,000 different species have been described.
Nematodes are found almost everywhere, in the sea, in fresh water and on land. Often, nematodes outnumber all other multicellular animals by species and numbers.
Nematodes have a long, worm-like shape and a round cross-section. Segmentation, such as exists in earthworms, is absent.