The organisms belonging to phylum Nematoda are roundworms, examples of which are ascaris, trichinella, filaria worms, hookworms and pinworms. Nematodes are part of a group of animals, known as ecdysozoans, that periodically shed their skin as they grow. Although nematodes are frequently found in nature, numerous species live as internal parasites in most vertebrates, including humans.
Phylum Nematoda is a sub-category of Kingdom Animalia, which consists of multicellular heterotrophs that require oxygen for survival. Under this phylum, taxonomists have already classified around 16 to 20 orders. Since the mid-1980s, more than 2,200 genera and 15,000 species have been identified.
The anatomy of nematodes includes a mouth, retracted piercing device, nerve ring, pharynx, intestine, ovary, pseudocoelom, cuticle, reproductive pore, anus and excretory pores. Although these organisms lack a circulatory system, roundworms possess a complete digestive tract. The pseudocoelom contains fluids that aid in the transportation of nutrients. Some nematodes, particularly those species that are abundant in soil, are grouped according to their feeding habits. Herbivores feed on plants, bacterivores on soil bacteria, fungivores on fungi, predators on other nematodes or similarly sized organisms and omnivores on several types of food sources. Members of the order Tylenchida, Rhabditida, Aphelenchida, Mononchida and Dorylaimida are generally considered as herbivores, bacterivores, fungivores, predators and omnivores, respectively.