Nematoda means thread like ones, the group was establishted in 1808 as Nematoidea by Karl Rudolphi. In 1837 it was reclassified by Burmeister as belonging to the Nematodes family, it was 1861 that K.M. Diesing renamed them Nematoda. During 1919 it was argued that the name should be Nemates or Nemata and Nemas in English by Nathan Cobb although he wasn’t successful. The roundworm is considered to be distinct and stands alone when it comes to scientific specifications.
Nematodes also known as roundworms belong to the phylum of Nematoda and are the most diversified member of the pseudocoelomates. They are also among the most diverse of animals in general. There have been more than eighty thousand nematodes described and more than fifteen thousand of those were parasites. There is believed to be over 500,000 nematodes in existence.
The nematode has managed to adapt itself to almost every environmental situation in the world. Ninety percent of the life on the bottom of the ocean is made up of nematodes. Pathogens in animals, plants and humans are included in the parasites; there are some that can go through cryptobiosis. This is where the nematodes metabolic rate and body functions slow down considerably to help them adjust to their environment and ensure survival.
There isn’t much actual knowledge about nematodes. They are normally divided into two classes. The Adenophorea which seems to be a paraphyletic assemblage of the nematodes that has kept a bit of the previous traits and the Secernentea which appears to be the closest relative are the two classes. DNA sequencing shows evidence of five clades which are Dorylaimia, Spirurina, Enoplia, Tylenchina and Rhabditina.
The roundworm isn’t segmented instead they are bilaterally symmetrical it has a full digestive system. The body is surrounded by a layer known as the cuticle to cover the epidermal cells. There isn’t a circulatory system to these animals however the pseudocoelom is used to send nutrients in the body fluid. The nematodes nervous system is fairly simple. Movement of the nematodes is accomplished by contracting the muscles which makes the body flex so the animal actually moves back and forth in a thrashing motion.
Nematodes that act as parasites on people are ascarids (Ascaris), hookworms, pinworms (Enterobius), filarids, and whipworms (Trichuris trichiura). Rats, pigs and humans can all be prone to the trichina worm (Trichinella spiralis) which is known to cause trichinosis. While normally attaching themselves to animals the baylisascaris can cause death in people as well.
There is a nematode that relies on the fig wasps. They use them to get to ripe figs and kill the wasps. The loss of crops is caused by nematodes that prey on crops. Whether or not a nematode helps or hurts plants will depend on the type.
Sources:
http://www.absoluteastronomy.com/topics/Nematode#encyclopedia
http://encyclopedia2.thefreedictionary.com/Cryptobiosis
http://animaldiversity.ummz.umich.edu/site/accounts/information/Nematoda.html
