Nematodes
Scientific classification
Kingdom: Animalia Phylum: Nematoda Rudolphi, 1808
Classes
Adenophorea    Subclass Enoplia    Subclass Chromadoria Secernentea    Subclass Rhabditia    Subclass Spiruria    Subclass Diplogasteria    Subclass Tylenchia

The nematodes or roundworms (Phylum Nematoda from Greek νῆμα (nema): "thread" + -ώδη -ode "like") are one of the most common phyla of animals, with over 80,000 different described species (over 15,000 are parasitic). Karl Asmund Rudolphi ( July 14, 1771 &ndash November 29, 1832) was a Swedish -born naturalist, who is credited with being Adenophorea is a class of Nematodes They are unsegmented worms Enoplia are a subclass of the Roundworms Most are free-living but the group includes the order Trichurida, which includes Whipworms and The Chromadoria are a subclass of the class Adenophorea, (belonging to the phylum Nematoda - roundworms Secernentea are a class of Nematodes characterised by numerous Caudal papillae and an Excretory system possessing lateral canals Subclass Rhabditia is mostly comprised of Parasitic Nematodes, though there are some free-living species as well Subclass Spiruria is comprised of mostly Parasitic Secernentean Nematodes. Diplogasterida is an order of Nematodes and the sole order of its subclass Diplogasteria. A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class. Greek (el ελληνική γλώσσα or simply el ελληνικά — "Hellenic" is an Indo-European language, spoken today by 15-22 million people mainly Parasitism is a type of symbiotic relationship between Organisms of different Species. They are ubiquitous in freshwater, marine, and terrestrial environments, where they often outnumber other animals in both individual and species counts, and are found in locations as diverse as Antarctica and oceanic trenches. The oceanic trenches are hemispheric-scale long but narrow topographic depressions of the sea floor Further, there are a great many parasitic forms, including pathogens in most plants, animals, and also in humans. A pathogen (from Greek πάθος pathos "suffering passion" and γἰγνομαι (γεν- gignomai (gen- "I give birth to" infectious

The nematodes were originally named nematoidea by Rudolphi (1808). Karl Asmund Rudolphi ( July 14, 1771 &ndash November 29, 1832) was a Swedish -born naturalist, who is credited with being They were renamed nematodes by Burmeister 1837 (as a family; Leuckart 1848 and von Siebold 1848 both promoted them to the rank of order), then nematoda (Diesing 1861), though Nathan Cobb (1919) argued that they should be called nemata or nemates (and in English 'nemas' rather than 'nematodes'). Karl Moriz Diesing (1800–1867 was an Austrian Naturalist and Zoologist, specializing in the study of Helminthology. Nathan Augustus Cobb ( 30 June, 1859 &ndash 4 June 1932) born in Spencer Massachusetts is known as "the father of Nematology After some confusion which saw the nematodes placed (often together with the horsehair worms, nematomorpha) as a class or order in various groups such as Aschelminthes, Lankester (1877) definitively promoted them to the level of phylum. Nematomorpha (sometimes called Gordiacea, and commonly known as Horsehair worms or Gordian worms) are a Phylum of Parasitic The Aschelminthes (also known as Aeschelminthes, Nemathelminthes, or Pseudocoelomata) closely associated with the Platyhelminthes, are an obsolete Sir E Ray Lankester KCB, FRS ( May 15, 1847 – August 13, 1929) was a British Zoologist, born in A phylum ( Plural: phyla) is a Taxonomic rank between Kingdom and above Class.

Contents 1 Morphology 2 Reproduction 3 Free-living species 4 Abundance 5 Parasitic species 6 Nematodes in Agriculture 7 Phylogeny 8 Robustness 9 See also 10 References 11 External links

Morphology

Roundworms are unsegmented, bilaterally symmetric and triploblastic protostomes with a complete digestive system. The Bilateria (ˌbaɪləˈtɪəriə are all animals having a bilateral symmetry, i Triploblasty is a condition of the Blastula in which there are three primary Germ layers the Ectoderm, Mesoderm, and Endoderm. Protostomia (from the Greek: mouth first) are a Taxon of Animals Together with the Deuterostomes and a few smaller phyla Digestion is the breaking down of chemicals in the body into a form that can be absorbed Roundworms have no circulatory or respiratory systems so they use diffusion to breathe. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement ^[1] Although they lack a circulatory system, nutrients are transported throughout the body via fluid in the pseudocoelom. They are thin and are round in cross section. Nematodes are one of the simplest animal groups to have a complete digestive system, with a separate orifice for food intake and waste excretion, a pattern followed by all subsequent, more complex animals. The body cavity is a pseudocoelom (persistent blastula), which lacks the muscles of coelomate animals that protects the body from drying out, from digestive juices, or from other harsh environments. By the broadest definition a body cavity is any fluid filled space in a Multicellular organism. The blastula is an early stage of Embryonic development in Animals It is also called blastosphere Although this cuticle allows movement and shape changes via a hydrostatic skeletal system, it is very inelastic so does not allow the volume of the worm to increase. A hydrostatic skeleton or hydroskeleton is a structure found in many Cold-blooded organisms and soft-bodied animals consisting of a fluid-filled cavity the Coelom Therefore, as the worm grows, it has to molt and form new cuticles. Ecdysis is the Molting of the Cuticula in Arthropods and related groups ( Ecdysozoa) The cuticles don't allow volume to increase so as to keep hydrostatic pressure inside the organism very high. For this reason, the roundworms do not possess circular muscles (just longitudinal ones) as they're not required. This hydrostatic pressure is the reason the roundworms are round.

Nematodes have a simple nervous system, with a main ventral nerve cord and a smaller dorsal nerve cord^[2]. The ventral nerve cords make up the Nervous system of some phyla of the Invertebrates particularly within the Nematodes Annelids and The dorsal nerve cord is one of the embryonic features unique to Chordates along with a Notochord, a post-anal tail and Pharyngeal slits The dorsal nerve Sensory structures at the anterior end are called amphids, while sensory structures at the posterior end are called phasmids. "Phasmid" redirects here For the cloning vector used in genetics see Phagemid.

Most free-living nematodes are microscopic, though a few parasitic forms can grow to over a meter in length (typically as parasites of very large animals such as whales). There are no circular muscles, so the body can only undulate from side to side. Muscle (from Latin musculus, diminutive of mus "mouse" is contractile tissue of the body and is derived from the Contact with solid objects is necessary for locomotion; its thrashing motions vary from mostly to completely ineffective at swimming.

Nematodes generally eat bacteria, fungi and protozoans, although some are filter feeders. The Bacteria ( singular: bacterium) are a large group of unicellular Microorganisms Typically a few Micrometres in length bacteria have A fungus (ˈfʌŋgəs is a eukaryotic Organism that is a member of the kingdom Fungi (ˈfʌndʒaɪ Protozoa (in Greek πρῶτον proton "first" and ζῷα zoia "animals" are unicellular Eukaryotes (singular Filter feeders (also known as suspension feeders) are Animals that feed by straining suspended matter and food particles from water typically by passing the water Excretion is through a separate excretory pore. Excretion is the process of eliminating waste products of Metabolism and other non-useful materials Nematodes also contract bacterial infections within excretion pores.

Reproduction

Reproduction is usually sexual. Males are usually smaller than females (often much smaller) and often have a characteristically bent tail for holding the female for copulation. Sexual intercourse, in its biological sense is the act in which the male reproductive organ (in humans and other higher animals enters the female reproductive tract During copulation, one or more chitinized spicules move out of the cloaca and are inserted into genital pore of the female. Chitin ( C 8 H 13 O 5 N)n (ˈkaɪtən is a long-chain Polymer of a N-acetylglucosamine This article is about the skeletal structure See also Spicule (solar physics and Spicule (glass manufacture. Amoeboid sperm crawl along the spicule into the female worm. Amoeboids are Unicellular lifeforms that mainly consist of Contractile vacuoles, a nucleus, and cytoplasm as their basic structure The term sperm is derived from the Greek word (σπέρμα sperma (meaning "seed" and refers to the male reproductive cells. Nematode sperm is thought to be the only eukaryotic cell without the globular protein G-actin. Animals Plants fungi, and Protists are eukaryotes (juːˈkærɪɒt or -oʊt Organisms whose cells are organized into complex Actin is a globular roughly 42-kDa Protein found in all eukaryotic cells (except for Nematode sperm where it may be present at concentrations of

Eggs may be embryonated or unembryonated when passed by the female, meaning that their fertilized eggs may not yet be developed. In free-living roundworms, the eggs hatch into larva, which eventually grow into adults; in parasitic roundworms, the life cycle is often much more complicated.

Some nematodes, specifically Heterorhabditis spp. Heterorhabditis is a Genus of Nematodes belonging to the order Rhabditida. , undergo a process called endotokia matricida; intrauterine birth causing maternal death. ^[3] The hermaphroditic nematode keeps its self-fertilized eggs inside its uterus until they hatch. The juvenile nematodes will then ingest the parent nematode. This process is significantly promoted in environments with a low or reducing food supply. ^[3]

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 algae, fungi, small animals, fecal matter, dead organisms and living tissues. Free-living marine nematodes are important and abundant members of the meiobenthos. Meiofauna are small benthic invertebrates that live in both marine and fresh water environments. 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 is Caenorhabditis elegans, which lives in the soil and has found much use as a model organism. Caenorhabditis elegans (ˌsiːnoʊræbˈdaɪtɪs ˈɛlɪgænz is a free-living Nematode (roundworm about 1  mm in length which A model organism is a Species that is extensively studied to understand particular biological Phenomena, with the expectation that discoveries made C. elegans has had its entire genome sequenced, as well as the developmental fate of every cell determined, and every neuron mapped.

Some nematodes can undergo cryptobiosis. Cryptobiosis is an ametabolic state of life entered by an animal's Organisms in response to adverse environmental conditions such as Desiccation, Freezing

Abundance

The nematode species are very difficult to distinguish. Of the pseudocoelomates, the nematodes are the most common. By the broadest definition a body cavity is any fluid filled space in a Multicellular organism. Nematodes have successfully adapted to nearly every niche from marine to fresh water, from the polar regions to the tropics, as well as the highest to the lowest of elevations. In Ecology, a niche (pronounced nich nēsh or nish A shorthand definition of niche is how an organism makes a living They represent, for example, 90% of all life on the seafloor of the Earth. [3] Though 20,000 species have been classified it is estimated that this number might be upwards of 500,000 if all were known. ^[4]. In certain fertile areas the topsoil is estimated to contain in the billions of nematodes per acre. Topsoil is the upper outermost layer of soil usually the top 2 to 8 inches The acre is a unit of Area in a number of different systems including the imperial and U ^[5] In the 1914 edition of the Yearbook of the United States Department of Agriculture N. A. Cobb wrote on the abundance of nematodes^[5]:

“	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 thin 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.	”
	— N. A. Cobb

Parasitic species

Nematodes commonly parasitic on humans include whipworms, hookworms, pinworms, ascarids, and filarids. The human whipworm ( Trichuris trichiura or Trichocephalus trichiuris) is a Roundworm, which causes Trichuriasis when it infects The hookworm is a parasitic Nematode worm that lives in the Small intestine of its host which may be a Mammal such as a Dog, The pinworm (Genus Enterobius) also known as threadworm is a Parasitic Roundworm of the phylum Nematoda. Ascariasis is a Human Disease caused by the parasitic Roundworm Ascaris lumbricoides. The species Trichinella spiralis, commonly known as the trichina worm, occurs in rats, pigs, and humans, and is responsible for the disease trichinosis. The species Trichinella spiralis is an important Parasite, occurring in rats pigs and humans and is responsible for the disease Trichinosis. Trichinosis, also called trichinellosis, or trichiniasis, is a Parasitic disease caused by eating raw or undercooked Pork and Wild game Baylisascaris usually infests wild animals but can be deadly to humans as well. Baylisascaris is a Genus of Roundworms that infest more than fifty animal Species. Haemonchus contortus is one of the most abundant infectious agents in sheep around the world, causing great economic damage to sheep farms. Haemonchus contortus, also known as red stomach worm wire worm or Barber's pole worm is very common parasite and one the most pathogenic Nematode of Ruminants In contrast, entomopathogenic nematodes parasitize insects and are considered by humans to be beneficial. Entomopathogenic nematodes are soil-inhabiting lethal insect Parasitoids that belong to the phylum Nematoda commonly called Roundworms The term entomopathogenic

One form of nematode is entirely dependent upon the wasps which are the sole source of fig fertilization. Ficus is a Genus of about 850 Species of woody Trees Shrubs Vines Epiphytes and hemi-epiphytes in the family 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.

Plant parasitic nematodes include several groups causing severe crop losses. The most common genera are: Aphelenchoides (foliar nematodes), Meloidogyne (root-knot nematodes), Heterodera, Globodera (cyst nematodes) such as the potato cyst nematode, Nacobbus, Pratylenchus (lesion nematodes), Ditylenchus, Xiphinema, Longidorus, Trichodorus. Foliar Nematodes are Plant parasitic roundworms in the genus Aphelenchoides. Potato root nematodes or potato cyst nematodes (PCN are 1-mm long roundworms belonging to the genus Globodera, which comprises around 12 species Several phytoparasitic nematode species cause histological damages to roots, including the formation of visible galls (Meloidogyne) 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 Xiphinema index, vector of GFLV (Grapevine Fanleaf Virus), an important disease of grapes.

Other nematodes attack bark and forest trees. The most important representative of this group is Bursaphelenchus xylophilus, the pine wood nematode, present in Asia and America and recently discovered in Europe.

The largest nematode ever recorded, Placentonema gigantissima, was discovered parasitizing the placenta of a sperm whale, measuring 8. 5 m in length with a diameter of 0. 3 mm, and containing 32 ovaries. ^[6]

Other large nematodes include: Dioctophyma renale, the giant kidney worm, a parasite most commonly found in mink but also in dogs and humans, that can reach up to 103 cm in length. Dioctophyma renale or the giant kidney worm is a common parasital worm found especially in carnivorous animals particularly Minks There are two living species of " mink," the American Mink and the European Mink. ^[7][6]

Nematodes in Agriculture

Depending on the species, a nematode may be beneficial or detrimental to plant health. The soybean cyst nematode (SCN Heterodera glycines, is a plant-parasitic Nematode and a devastating pest of the Soybean ( Glycine

From an agricultural perspective, there are two categories of nematode: predatory ones, which will kill garden pests like cutworms, and pest nematodes, like the root-knot nematode, which attack plants. The term cutworm is used for the Larvae of many species of Moth. Root-knot nematodes are plant-parasitic Nematodes from the genus Meloidogyne.

Predatory nematodes can be bred by soaking a specific recipe of leaves and other detritus in water, in a dark, cool place, and can even be purchased as an organic form of pest control. In Biology, detritus is non-living particulate organic material (as opposed to dissolved organic material The organic movement broadly refers to the organizations and individuals involved worldwide in the promotion of organic farming which they believe to be a more sustainable mode of Pest control refers to the regulation or management of a Species defined as a pest, usually because it is perceived to be detrimental to a person's Health

Rotations of plants with nematode resistant species or varieties is one means of managing parasitic nematode infestations.

Phylogeny

Morphological characters and molecular phylogenies place the Nematoda as sister taxon to the parasitic Nematomorpha (together Nematoida). The Nematodes belong to the Cyclioneuralia, a clade that consists out of Nematoida, Pripulida, Loricifera and Kinorhyncha. The cloesest relatives of these animals are the arthropods (insects, crustaceans, myriapods and chelicerates). All these molting animals form a clade called Ecdysozoa (Aguinaldo et al 1998; Dunn et al 2008).

That the roundworms have a large number of peculiar apomorphies and in many cases a parasitic lifestyle confounds analyses; the DNA sequence data hitherto analyzed is equivocal on ecdysozoan monophyly. Cladistics is the hierarchical classification of Species based on evolutionary ancestry A DNA sequence or genetic sequence is a succession of letters representing the Primary structure of a real or hypothetical DNA Molecule A clade is a taxonomic group comprising a single Common ancestor and all the descendants of that ancestor Genetic analyses of roundworms suggest that - as is also indicated by their unique morphological features - the group has been under intense selective pressure during its early radiation, resulting apparently in accelerated rates of both morphological and molecular evolution. Natural selection is the process by which favorable Heritable traits become more common in successive Generations of a Population of

Robustness

• Hundreds of nematode worms (C. elegans), featured in a research project on mission STS-107, survived the Space Shuttle Columbia Disaster. STS-107 was a Space shuttle mission by NASA using the Space Shuttle Columbia, launched January 16, 2003. The Space Shuttle Columbia disaster occurred on February 1, 2003, when the Space Shuttle ''Columbia'' disintegrated over Texas ^[8]

See also

• Ascariasis: A human disease caused by the parasitic roundworm Ascaris lumbricoides
• Caenorhabditis elegans: An important model organism often used to study cellular differentiation, sometimes referred to as "worm" by scientists. Ascariasis is a Human Disease caused by the parasitic Roundworm Ascaris lumbricoides. Caenorhabditis elegans (ˌsiːnoʊræbˈdaɪtɪs ˈɛlɪgænz is a free-living Nematode (roundworm about 1  mm in length which A model organism is a Species that is extensively studied to understand particular biological Phenomena, with the expectation that discoveries made In Developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized Cell type.
• List of parasites (human)
• Toxocariasis: A helminth infection of humans caused by the dog or cat roundworm, Toxocara canis or Toxocara cati
• Xiphinema: List of species

References

External links

• http://www.ucmp.berkeley.edu/phyla/ecdysozoa/nematoda.html
• Nematode.net: Repository of parasitic nematode sequences.
• http://www.nematodes.org/
• NeMys World free-living Marine Nematodes database
• Nematode Virtual Library
• International Federation of Nematology Societies
• Society of Nematologists
• Australasian Association of Nematologists
• Research on nematodes and longevity

© 2009 citizendia.org; parts available under the terms of GNU Free Documentation License, from http://en.wikipedia.org
Dapyx Software network: MP3 Explorer | Ebook Manager | Zenithic