The nematodes from the phylum nematoda are one of the most diverse of all animals. They are very difficult to distinguish because there are over 80,000 described. Nematodes have adapted to every niche from marine to fresh water, polar to the tropics, as well as the highest to the lowest of elevations. They also represent 90% of all life on the seafloor. They are the most numerous multicellular animals on earth. Thousands can be present in a handful of soil.

Nematodes are simple organisms because adult nematodes are comprised of approximately 1,000 somatic cells, and potentially hundreds of cells associated with the reproductive system. As well as they have been characterized as a tube within a tube because of its digestive canal which goes from its mouth to the anus. Nematodes have digestive, nervous, excretory, and reproductive systems, but do not have circulatory or respiratory systems. Their size ranges from 0.3 mm to over  8 meters.(University of Nebraska)

(Image from Wikipedia, http://en.wikipedia.org/wiki/Nematode)