• Nematodes, 1837 • Nematoidea sensu stricto Cobb, 1919 • Nemates Cobb, 1919 • Nemata Cobb, 1919 emend. The nematodes (:,: ) or roundworms constitute the Nematoda (also called Nemathelminthes). They are a diverse animal phylum inhabiting a broad range of environments.

Nematode can be difficult to distinguish, and although over 25,000 have been described, of which more than half are, the total number of nematode species has been estimated to be about 1 million. Nematodes are classified along with and other in the, and, unlike, have tubular with openings at both ends. Nematodes have successfully adapted to nearly every from marine (salt water) to fresh water, to soils, and from the polar regions to the tropics, as well as the highest to the lowest of elevations. They are ubiquitous in freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and counts, and are found in locations as diverse as mountains, deserts and.

They are found in every part of the earth's, even at great depths, 0.9–3.6 km (3,000–12,000 ft), below the surface of the Earth in gold mines in South Africa. They represent 90% of all animals on the. Their numerical dominance, often exceeding a million individuals per square meter and accounting for about 80% of all individual animals on earth, their diversity of life cycles, and their presence at various trophic levels point at an important role in many ecosystems. The many parasitic forms include in most plants and animals (including ). Some nematodes can undergo., a nematologist, described the ubiquity of nematodes on Earth thus: In short, if all the matter in the universe except the nematodes were swept away, our world would still be dimly recognizable, and if, as disembodied spirits, we could then investigate it, we should find its mountains, hills, vales, rivers, lakes, and oceans represented by a film of nematodes.

The location of towns would be decipherable, since for every massing of human beings there would be a corresponding massing of certain nematodes. Trees would still stand in ghostly rows representing our streets and highways. The location of the various plants and animals would still be decipherable, and, had we sufficient knowledge, in many cases even their species could be determined by an examination of their erstwhile nematode parasites. Internal anatomy of a male C.

Proposed solutions include the definition of regions with a negligible risk for Trichinella in fattening pigs or the certification of Trichinella-free pig production units. Information on species and genotype distribution and host range can be downloaded from the website of the International Trichinella Reference Centre.

Elegans nematode Nematodes are small, slender worms: typically approximately 5 to 100 µm thick, and 0.1 to 2.5 mm long. The smallest nematodes are microscopic, while free-living species can reach as much as 5 cm (2 in), and some parasitic species are larger still, reaching over 1 m (3 ft) in length.: 271 The body is often ornamented with ridges, rings, bristles, or other distinctive structures. The head of a nematode is relatively distinct. Whereas the rest of the body is bilaterally symmetrical, the head is radially symmetrical, with sensory bristles and, in many cases, solid 'head-shields' radiating outwards around the mouth. The mouth has either three or six lips, which often bear a series of teeth on their inner edges.

An adhesive 'caudal gland' is often found at the tip of the tail. The is either a or a single layer of cells, and is covered by a thick.

The cuticle is often of complex structure, and may have two or three distinct layers. Building Construction Pictures here. Underneath the epidermis lies a layer of longitudinal cells. The relatively rigid cuticle works with the muscles to create a hydroskeleton as nematodes lack circumferential muscles. Projections run from the inner surface of muscle cells towards the; this is a unique arrangement in the animal kingdom, in which nerve cells normally extend fibres into the muscles rather than vice versa. Digestive system [ ] The oral cavity is lined with cuticle, which is often strengthened with ridges or other structures, and, especially in carnivorous species, may bear a number of teeth.

The mouth often includes a sharp, which the animal can thrust into its prey. In some species, the stylet is hollow, and can be used to suck liquids from plants or animals. The oral cavity opens into a muscular, sucking, also lined with cuticle. Digestive glands are found in this region of the gut, producing that start to break down the food. In stylet-bearing species, these may even be injected into the prey.

There is no, with the pharynx connecting directly to a muscleless that forms the main length of the gut. This produces further, and also absorbs nutrients through its single cell thick lining. The last portion of the intestine is lined by cuticle, forming a, which expels waste through the just below and in front of the tip of the tail.

Movement of food through the digestive system is the result of body movements of the worm. The intestine has valves or at either end to help control the movement of food through the body. Excretory system [ ] is excreted in the form of through the body wall, and is not associated with any specific organs.

However, the structures for excreting salt to maintain are typically more complex. In many marine nematodes, one or two unicellular ' excrete salt through a pore on the underside of the animal, close to the pharynx. In most other nematodes, these specialised cells have been replaced by an organ consisting of two parallel ducts connected by a single transverse duct. This transverse duct opens into a common canal that runs to the excretory pore. Nervous system [ ]. See also: Four peripheral run the length of the body on the dorsal, ventral, and lateral surfaces.

Each nerve lies within a cord of connective tissue lying beneath the and between the cells. The ventral nerve is the largest, and has a double structure forward of the. The dorsal nerve is responsible for motor control, while the lateral nerves are sensory, and the ventral combines both functions. The nervous system is also the only place in the nematode body that contains, which are all non-motile and with a sensory function.

At the anterior end of the animal, the nerves branch from a dense, circular nerve () round surrounding the, and serving as the. Smaller nerves run forward from the ring to supply the sensory organs of the head. The bodies of nematodes are covered in numerous sensory and that together provide a sense of touch. Behind the sensory bristles on the head lie two small pits, or '.

These are well supplied with nerve cells, and are probably organs. A few aquatic nematodes possess what appear to be eye-spots, but is unclear whether or not these are actually sensory in nature. Reproduction [ ]. Extremity of a male nematode showing the, used for copulation.

Bar = 100 µm Most nematode species are, with separate male and female individuals, though some, such as, are, consisting of and rare males. Both sexes possess one or two tubular. In males, the sperm are produced at the end of the gonad and migrate along its length as they mature. The testis opens into a relatively wide and then during intercourse into a glandular and muscular ejaculatory duct associated with the and. In females, the ovaries each open into an (in hermaphrodites, the eggs enter a first) and then a glandular. The uteri both open into a common vulva/ vagina, usually located in the middle of the morphologically ventral surface.

Reproduction is usually sexual, though hermaphrodites are capable of self-fertilization. Males are usually smaller than females/ hermaphrodites (often much smaller) and often have a characteristically bent or fan-shaped tail. During, one or more move out of the cloaca and are inserted into the genital pore of the female.

Crawl along the spicule into the female worm. Nematode sperm is thought to be the only without the globular protein. Eggs may be or unembryonated when passed by the female, meaning their fertilized eggs may not yet be developed. A few species are known to be. The eggs are protected by an outer shell, secreted by the uterus. In free-living roundworms, the eggs hatch into, which appear essentially identical to the adults, except for an underdeveloped reproductive system; in parasitic roundworms, the life cycle is often much more complicated. Nematodes as a whole possess a wide range of modes of reproduction.

Some nematodes, such as spp., undergo a process called: intrauterine birth causing maternal death. Some nematodes are, and keep their self-fertilized eggs inside the until they hatch. The juvenile nematodes will then ingest the parent nematode. This process is significantly promoted in environments with a low food supply. The nematode model species and exhibit, which is very rare among animals. The single (root-knot nematodes) exhibit a range of reproductive modes, including, (in which most, but not all, generations reproduce asexually), and both and.

The genus exhibits an unusual form of parthenogenesis, in which sperm-producing males copulate with females, but the sperm do not fuse with the ovum. Contact with the sperm is essential for the ovum to begin dividing, but because there is no fusion of the cells, the male contributes no genetic material to the offspring, which are essentially of the female. Free-living species [ ] In free-living species, development usually consists of four molts of the cuticle during growth. Different species feed on materials as varied as,, small animals, fecal matter, dead organisms, and living tissues. Free-living marine nematodes are important and abundant members of the. They play an important role in the decomposition process, aid in recycling of nutrients in marine environments, and are sensitive to changes in the environment caused by pollution.

One roundworm of note,, lives in the soil and has found much use as a. Elegans has had its entire genome sequenced, as well as the developmental fate of every cell determined, and every neuron mapped.

Parasitic species [ ]. Eggs (mostly nematodes) from stools of wild Nematodes commonly parasitic on humans include ( Ascaris),,, ( Enterobius), and ( Trichuris trichiura). The species, commonly known as the 'trichina worm', occurs in rats, pigs, and humans, and is responsible for the disease.

Usually infests wild animals, but can be deadly to humans, as well. Are known for causing heartworm disease by inhabiting the hearts, arteries, and lungs of dogs and some cats. Is one of the most abundant infectious agents in sheep around the world, causing great economic damage to sheep. In contrast, parasitize insects and are mostly considered beneficial by humans, but some attack beneficial insects. One form of nematode is entirely dependent upon, which are the sole source of fertilization. They prey upon the wasps, riding them from the ripe fig of the wasp's birth to the fig flower of its death, where they kill the wasp, and their offspring await the birth of the next generation of wasps as the fig ripens.

A newly discovered parasitic tetradonematid nematode,, apparently induces fruit mimicry in the tropical ant. Infected ants develop bright red (abdomens), tend to be more sluggish, and walk with their gasters in a conspicuous elevated position. It is likely that these changes cause birds to confuse the infected ants for berries, and eat them. Parasite eggs passed in the bird's are subsequently collected by foraging Cephalotes atratus and are fed to their, thus completing the life cycle of M. Similarly, multiple varieties of nematodes have been found in the abdominal cavities of the primitively social sweat bee,. Inside the female body, the nematode hinders ovarian development and renders the bee less active and thus less effective in pollen collection.

Colorized of ( Heterodera sp.) and egg Plant-parasitic nematodes include several groups causing severe crop losses. The most common genera are (),, (potato cyst nematodes), (soybean cyst nematodes),, (),, (lesion nematodes), and (dagger nematodes). Several phytoparasitic nematode species cause histological damages to roots, including the formation of visible galls (e.g. By root-knot nematodes), which are useful characters for their diagnostic in the field. Some nematode species transmit plant viruses through their feeding activity on roots.

One of them is, vector of, an important disease of grapes, another one is, vector of. Other nematodes attack bark and forest trees. The most important representative of this group is, the pine wood nematode, present in Asia and America and recently discovered in Europe. Agriculture and horticulture [ ] Depending on the species, a nematode may be beneficial or detrimental to plant health. From agricultural and perspectives, the two categories of nematodes are the predatory ones, which will kill garden pests like and, and the pest nematodes, like the, which attack plants, and those that act as spreading between crop plants.

Predatory nematodes can be bred by soaking a specific recipe of leaves and other in water, in a dark, cool place, and can even be purchased as an form of. Rotations of plants with nematode-resistant species or varieties is one means of managing parasitic nematode infestations. For example,, grown over one or more seasons (the effect is cumulative), can be used to control nematodes. Another is treatment with natural antagonists such as the fungus., a natural biocontrol, elicits plant defense responses to destroy parasitic nematodes on roots of,,,, and crops without harming beneficial nematodes in the soil. Is an efficient method to kill nematodes before planting a crop, but indiscriminately eliminates both harmful and beneficial soil fauna. The golden nematode is a particularly harmful variety of nematode pest that has resulted in quarantines and crop failures worldwide. Has found a 13- to 14-fold reduction of nematode population densities in plots having green manure or seed meal in the soil.

Epidemiology [ ]. Effect of on A number of intestinal nematodes cause diseases affecting human beings, including, and. Filarial nematodes cause. Soil ecosystems [ ] Ninety percent of nematodes reside in the top 15 cm of soil. Nematodes do not decompose organic matter, but, instead, are parasitic and free-living organisms that feed on living material. Nematodes can effectively regulate bacterial population and community composition — they may eat up to 5,000 bacteria per minute.

Also, nematodes can play an important role in the by way of nitrogen mineralization. One group of, the, are predators of soil nematodes. They set enticements for the nematodes in the form of lassos or adhesive structures. Society and culture [ ] Nematode worms ( C. Elegans), part of an ongoing research project conducted on the mission, survived the. It is believed to be the first known life-form to survive a virtually unprotected atmospheric descent to Earth's surface. See also [ ] • • •: An important often used to study, sometimes simply referred to as 'worm' by scientists • • •: A infection of humans caused by the or roundworm,.

• Atkinson, H.J. 59 (1): 255–266. Retrieved 4 Nov 2008. • Gubanov, N.M. 'Giant nematoda from the placenta of Cetacea; Placentonema gigantissima nov. 77 (6): 1123–1125.

[in Russian]. • Kaya, Harry K. 'An Overview of Insect-Parasitic and Entomopathogenic Nematodes'. In Bedding, R.A..

Csiro Publishing.. CS1 maint: Uses authors parameter () CS1 maint: Uses editors parameter () •.

Retrieved 10 Feb 2007. • White JG, Southgate E, Thomson JN, Brenner S (August 1976). 'The structure of the ventral nerve cord of Caenorhabditis elegans'. 275 (938): 327–48... • Lee, Donald L, ed. London: Taylor & Francis..

Retrieved 16 December 2014. • De Ley, P & Blaxter, M (2004).

'A new system for Nematoda: combining morphological characters with molecular trees, and translating clades into ranks and taxa'. In R Cook & DJ Hunt. Nematology Monographs and Perspectives. Brill, Leiden. CS1 maint: Uses authors parameter () CS1 maint: Uses editors parameter () External links [ ] Wikimedia Commons has media related to.