Phylum Nematoda
Nematodes, or roundworms, (Fig. 1) are translucent, slender, unsegmented, cylindrical pseudocoelomate worms. The body typically tapers at the posterior end. Nematodes are dioecious. Most nematodes are parasitic in plants and animals. Free-living nematodes feed on organic matter, algae and diatoms. Parasitic nematodes cause both public health and economic problems.