Nematoda

=Phylum Nematoda (means "thread form") = Roundworms (nematodes) are bilaterally symmetrical, worm-like organisms that are surrounded by a strong, flexible noncellular layer called a cuticle. Their body plan is simple. The cuticle is secreted by and covers a layer of epidermal cells. Near the body wall but under the epidermal cells are muscle cells; they run in the longitudinal direction only. A true coelom is lacking, instead, nematodes have a "pseudocoel" formed directly from the cavity of the blastula (rather than as a result of the division or folding of mesoderm). The cavity of the pseudocoel is small, being mostly filled with an intestine and oviducts or testes. A simple nervous system consists of a ring of nervous tissue around the pharynx that gives rise to dorsal and ventral nerve cords running the length of the body. Nematodes move by contraction of the longitudinal muscles. Because their internal pressure is high, this causes the body to flex rather than flatten, and the animal moves by thrashing back and forth. No cilia or flagellae are present.

Some nematodes have specialized cells that excrete nitrogenous wastes; in others, canals or canals plus these specialized cells are present. Nematodes do not have flame cells. Most nematodes are dioecious. Fertilization takes place when males use special copulatory spines to open the females' reproductive tracts and inject sperm into them. The sperm are unique in that they lack flagellae and move by pseudopodia, like amoebas. Development of fertilized eggs is usually direct.

Nematodes are almost unbelievably abundant. One study reported around 90,000 individual nematodes in a single rotting apple. Another reported 236 species living in a few cubic centimeters of mud. The number of described species is around 12,000, but too little attention has been paid to these animals and the true number may be closer to 500,000. Some species are generalists, occuring across wide areas and in many habitats; others are much more specialized. Nematodes have colonized nearly every conceivable habitat on earth.

Many nematodes are free living and play critical ecological roles as decomposers and predators on microorganisms. But nematodes also include parasitic species, a number of which affect humans directly or indirectly through their domestic animals. These include the common roundworms, which probably infest more than half the world's humans; hookworms; trichina, the worms that cause trichinosis; pinworms, another extremely common parasite, even in the United States, which can be transmitted from human to human by eggs floating in household dust; and filarial worms, primarily tropical parasites that cause diseases such as filariasis (elephantiasis) and onchocerciasis (river blindness).

//**Rhabditae-**// both free-living and parasites (pin worms, hook worms, ascaris worms, filarial worms) //**Enoplea-**// mostly free-living but some parasites (whip worms, trichenella worms)
 * Classes of Nematoda:**

**Student Zoo Keeper Pages of Species: (Enter Your Species Pages Below)**
Guinea Worm (Zookeeper: Sidney Baker) Guinea Worm; //Dracunculus insignis// (Zookeeper: Taylor Cebuly) Stem Eelworm (Zookeeper: Kenzie Davidson) Heartworm (Zookeeper: Shaiann Etwara) Labronema ferox (Zookeeper: Erin Holbert) Myromeconema neotropicum (Zookeeper: Syed Islam) Brugia Roundworm(Zookeeper: Marissa Jenkins) Cephalobus persegnis (Zookeeper: Hannah Jones) Soybean Cyst Nematode (Zookeeper: James K. Kanthachack) Aporcelaimellus porcus (Zookeeper: Savannah Kelley) Ancylostoma duodenale (Zookeeper: Tori Lopez) Uncinaria stenocephala ( Zookeeper Whopper) Necator Americanus (Zookeeper: Heath McGregor) Whipworm2 (Zookeeper: Ramon Prieto) Root Knot Worm (Zookeeper: Lindsey Rafus) Seatworm ( Zookeeper: Sarah Reimer) Takamangai confusa (Zookeeper: Paco Rodriguez) Large Intestinal Roundworm (Zookeeper: Paige Ryder) Loa Loa Eye Worm (Zookeeper: Haley Shelton) __Pinworm__ (Zookeeper: Jeffrey Slape) Caenorhabditis elegans (Zookeeper: Riley Stewart) Round Worm- Mermis Nigrescens (Zookeeper: Jessica Tolliver) Whipworm (Zookeeper Rachel Tolliver) Hookworm-->necator americanus (Zookeeper: Ashley Veilleux) Ascaris Lumbricoides (Zookeeper: Hannah WIlliams) Bellarmine (Zookeeper: Johnta Williams) Vinegar Eels (Zookeeper: Jayme Willingham) __Gastrotricha__ (Zookeeper: Jesse Wilson) Filarial Worms (Zookeeper: Katie Woolen)

Myers, P. 2001. "Nematoda" (On-line), Animal Diversity Web. Accessed March 06, 2011 http://animaldiversity.ummz.umich.edu/site/accounts/information/Nematoda.html. scienceblogs.com health.medicscientist.com
 * Information and Photo References:**