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A worm is a common name given to a diverse group of invertebrate animals that have a long, soft body and no legs. There are hundreds of thousands of species of worms, 2,700 of these are earthworms. Animals which are commonly called worms include species of annelids, insects (their immature larva stage), and flatworms. Many marine and freshwater species, which are usually seen only by professional biologists, are recognized as "worms".
Distribution and habitat[edit | edit source]
Worms live in almost all parts of the world including marine, freshwater, and terrestrial habitats. Some worms living in the ground help to condition the soil (e.g., annelids, aschelminths). Many thrive as parasites of plants (e.g., aschelminths) and animals, including humans (e.g., platyhelminths, aschelminths). Several other worms may be free-living, or nonparasitic. There are worms that live in freshwater, seawater, and even on the seashore. Ecologically, worms form an important link in the food chains in virtually all the ecosystems of the world.
Classification[edit | edit source]
In everyday language, the term worm is also applied to various other living forms such as larvae, insects, centipedes, shipworms (teredo worms), or even some vertebrates (creatures with a backbone) such as blindworms and caecilians. Worms can be divided into several groups,
- The first of these includes the flatworms. This phylum is called Platyhelminthes. They have a flat, ribbon- or leaf-shaped body with a pair of eyes at the front. Some are parasites.
- The second group contains the threadworms, roundworms, and hookworms. This phylum is called Nematoda. Threadworms may be microscopic, such as the vinegar eelworm, or more than 1 meter (3 feet) long. They are found in damp earth, moss, decaying substances, fresh water, or salt water. Some roundworms are also parasites. The Guinea worm, for example, gets under the skin of the feet and legs of people living in tropical countries.
- The third group consists of the segmented worms, with bodies divided into segments, or rings. This phylum is called Annelida. Among these are the earthworms and the bristle worms of the sea.
In earlier taxonomic classification, all the above were included in the now obsolete group vermes.
There are hundreds of thousands of species that live in a wide variety of habitats other than soil. Over time this broad definition narrowed to the modern definition, although this still includes several different animal groups. Phyla that include worms include:
- Acanthocephala (spiny-headed worms)
- Annelida (segmented worms)
- Chaetognatha (arrow worms)
- Gnathostomulid (jaw worms)
- Hemichordata (acorn/tongue worms)
- Nematoda (roundworms)
- Nematomorpha (horsehair worms)
- Nemertea (ribbonworms)
- Onychophora (velvet worms)
- Phoronida (horseshoe worms)
- Platyhelminthes (flatworms)
- Priapulida (phallus worms)
- Sipuncula (peanut worms)
The most common worm is the earthworm, a member of phylum Annelida. Earthworms in general have been around for 120 million years, evolving during the time of the dinosaurs. They enrich and aerate the soil; Charles Darwin found that worms turn over the top six inches (15 cm) of topsoil every 20 years. They lack a brain but have nerve centers (called ganglia); they also lack eyes but can sense light with photoreceptors. Worms are hermaphrodites (both sexes in one animal) but can cross fertilize.
Worms may also be called helminths, particularly in medical terminology when referring to parasitic worms, especially the Nematoda (roundworms) and Cestoda (tapeworms). Hence "helminthology" is the study of parasitic worms. When an animal, such as a dog, is said to "have worms", it means that it is infested with parasitic worms, typically roundworms or tapeworms.
Characteristics[edit | edit source]
Worms usually have a cylindrical, flattened, or leaf-like body shape and are often without any true limbs or appendages. Instead, they may have bristles or fins that help them move. A few have light-sensing organs. Worms vary in size from less than 1 mm (0.04 inch) in certain aschelminths to more than 30 m (100 feet) in certain ribbon worms.
Some worms reproduce sexually. Hermaphroditism, the condition in which a single individual possesses both male and female reproductive parts, is common in many groups of worms. Asexual reproduction, whereby new individuals develop from the body cells of another, also occurs in some worms.
Worm species differ in their abilities to move about on their own. Many species have bodies with no major muscles, and cannot move on their own — they must be moved by forces or other animals in their environment. Many other species have bodies with major muscles and can move on their own; they are a type of muscular hydrostat. Many species of worms are decomposers; they break down dead plants and animals to return nutrients to the soil.
Worms as model organisms[edit | edit source]
Learning in the worm[edit | edit source]
See also[edit | edit source]
References & Bibliography[edit | edit source]
Key texts[edit | edit source]
Books[edit | edit source]
Papers[edit | edit source]
- Baheti, N. N., Sreedharan, M., Krishnamoorthy, T., Nair, M. D., & Radhakrishnan, K. (2008). Eosinophilic meningitis and an ocular worm in a patient from Kerala, South India: Journal of Neurology, Neurosurgery & Psychiatry Vol 79(3) Mar 2008, 271.
- Barr, M. M., & Sternberg, P. W. (1999). A polycystic kidney-disease gene homologue required for male mating behaviour in C. elegans: Nature Vol 401(6751) Sep 1999, 386-389.
- Burrell, B. D., & Sahley, C. L. (2004). Multiple Forms of Long-Term Potentiation and Long-Term Depression Converge on a Single Interneuron in the Leech CNS: Journal of Neuroscience Vol 24(16) Apr 2004, 4011-4019.
- Cacciatore, T. W., Rozenshteyn, R., & Kristan, W. B., Jr. (2000). Kinematics and modeling of leech crawling: Evidence for an oscillatory behavior produced by propagating waves of excitation: Journal of Neuroscience Vol 20(4) Feb 2000, 1643-1655.
- Chen, Z., Zheng, M., Friesen, W. O., & Iwasaki, T. (2008). Multivariable harmonic balance analysis of the neuronal oscillator for leech swimming: Journal of Computational Neuroscience Vol 25(3) Dec 2008, 583-606.
- da Rosa, C. E., Bianchini, A., & Monserrat, J. M. (2008). Antioxidant responses of Laeonereis acuta (Polychaeta) after exposure to hydrogen peroxide: Brazilian Journal of Medical and Biological Research Vol 41(2) Apr 2008, 117-121.
- Ebrahimi, C. M., & Rankin, C. H. (2007). Early patterned stimulation leads to changes in adult behavior and gene expression in C. elegans: Genes, Brain & Behavior Vol 6(6) Aug 2007, 517-528.
- Esch, T., Mesce, K. A., & Kristan, W. B. (2002). Evidence for Sequential Decision Making in the Medicinal Leech: Journal of Neuroscience Vol 22(24) Dec 2002, 11045-11054.
- Evason, K., Huang, C., Yamben, I., Covey, D. F., & Kornfeld, K. (2005). Anticonvulsant Medications Extend Worm Life-Span: Science Vol 307(5707) Jan 2005, 258-262.
- Faumont, S., & Lockery, S. R. (2006). The Awake Behaving Worm: Simultaneous Imaging of Neuronal Activity and Behavior in Intact Animals at Millimeter Scale: Journal of Neurophysiology Vol 95(3) Mar 2006, 1976-1981.
- Friesen, W. O., & Kristan, W. B. (2007). Leech locomotion: Swimming, crawling, and decisions: Current Opinion in Neurobiology Vol 17(6) Dec 2007, 704-711.
- Gabel, C. V., Gabel, H., Pavlichin, D., Kao, A., Clark, D. A., & Samuel, A. D. T. (2007). Neural circuits mediate electrosensory behavior in Caenorhabditis elegans: Journal of Neuroscience Vol 27(28) Jul 2007, 7586-7596.
- Geissler, P. W. (1998). 'Worms are our life', part I: Understandings of worms and the body among the Luo of western Kenya: Anthropology & Medicine Vol 5(1) Apr 1998, 63-79.
- Gray, J. M., Hill, J. J., & Bargmann, C. I. (2005). A circuit for navigation in Caenorhabditis elegans: PNAS Proceedings of the National Academy of Sciences of the United States of America Vol 102(9) Mar 2005, 3184-3191.
- Green, E. S., Zangerl, A. R., & Berenbaum, M. R. (1998). Reduced aggressive behavior: A benefit of silk-spinning in the parsnip webworm, Depressaria pastinacella (Lepidoptera: Occophoridae): Journal of Insect Behavior Vol 11(6) Nov 1998, 761-772.
- Hamamichi, S., Rivas, R. N., Knight, A. L., Cao, S., Caldwell, K. A., & Caldwell, G. A. (2008). Hypothesis-based RNAi screening identifies neuroprotective genes in a Parkinson's disease model: PNAS Proceedings of the National Academy of Sciences of the United States of America Vol 105(2) Jan 2008, 728-733.
- Hardege, J. D., Bartels-Hardege, H., Muller, C. T., & Beckmann, M. (2004). Peptide pheromones in female Nereis succinea: Peptides Vol 25(9) Sep 2004, 1517-1522.
- Hasegawa, K., Saigusa, T., & Tamai, Y. (2005). Caenorhabditis elegans opens up new insights into circadian clock mechanisms: Chronobiology International Vol 22(1) Feb 2005, 1-19.
- Houthoofd, K., Johnson, T. E., & Vanfleteren, J. R. (2005). Dietary Restriction in the Nematode Caenorhabditis elegans: Journals of Gerontology: Series A: Biological Sciences and Medical Sciences Vol 60A(9) Sep 2005, 1125-1131.
- Jansen, G., & Segalat, L. (2007). Behavioral genetics in the nematode Caenorhabditis elegans. Boca Raton, FL: CRC Press.
- Johnston, R. J., Jr., & Hobert, O. (2003). A microRNA controlling left/right neuronal asymmetry in Caenorhabditis elegans: Nature Vol 426(6968) Dec 2003, 845-849.
- Karbowski, J., Schindelman, G., Cronin, C. J., Seah, A., & Sternberg, P. W. (2008). Systems level circuit model of C. elegans undulatory locomotion: Mathematical modeling and molecular genetics: Journal of Computational Neuroscience Vol 24(3) Jun 2008, 253-276.
- Kleemann, G. A., & Basolo, A. L. (2007). Facultative decrease in mating resistance in hermaphroditic Caenorhabditis elegans with self-sperm depletion: Animal Behaviour Vol 74(5) Nov 2007, 1339-1347.
- Koizumi, O. (2007). Nerve Ring of the Hypostome in Hydra: Is It an Origin of the Central Nervous System of Bilaterian Animals: Brain, Behavior and Evolution Vol 69(2) Jan 2007, 151-159.
- Kornfeld, K., & Evason, K. (2006). Effects of Anticonvulsant Drugs on Life Span: Archives of Neurology Vol 63(4) Apr 2006, 491-496.
- Kulkarni, G., Li, H., & Wadsworth, W. G. (2008). CLEC-38, a transmembrane protein with C-type lectin-like domains, negatively regulates UNC-40-mediated axon outgrowth and promotes presynaptic development in Caenorhabditis elegans: Journal of Neuroscience Vol 28(17) Apr 2008, 4541-4550.
- Lanczik, M. H., Hofberg, K., & Brockington, I. F. (1999). Delusion of infestation with post-partum onset: Case report: Psychopathology Vol 32(5) Sep-Oct 1999, 277-280.
- Levy-Strumpf, N., & Culotti, J. G. (2007). VAB-8, UNC-73 and MIG-2 regulate axon polarity and cell migration functions of UNC-40 in C. elegans: Nature Neuroscience Vol 10(2) Feb 2007, 161-168.
- Link, C. D. (2005). Invertebrate models of Alzheimer's disease: Genes, Brain & Behavior Vol 4(3) Apr 2005, 147-156.
- Liu, T., Kim, K., Li, C., & Barr, M. M. (2007). FMRFamide-like neuropeptides and mechanosensory touch receptor neurons regulate male sexual turning behavior in Caenorhabditis elegans: Journal of Neuroscience Vol 27(27) Jul 2007, 7174-7182.
- Lucanic, M. S. (2008). An investigation of the signaling pathways that control cell migration and axon guidance in Caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Margeta, M. A., Shen, K., & Grill, B. (2008). Building a synapse: Lessons on synaptic specificity and presynaptic assembly from the nematode C. elegans: Current Opinion in Neurobiology Vol 18(1) Feb 2008, 69-76.
- McCormick, A. V. (2007). Modeling epilepsy in the nematode caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Miller, A. C., Thiele, T. R., Faumont, S., Moravec, M. L., & Lockery, S. R. (2005). Step-Response Analysis of Chemotaxis in Caenorhabditis elegans: Journal of Neuroscience Vol 25(13) Mar 2005, 3369-3378.
- Mori, I., Sasakura, H., & Kuhara, A. (2007). Worm thermotaxis: A model system for analyzing thermosensation and neural plasticity: Current Opinion in Neurobiology Vol 17(6) Dec 2007, 712-719.
- Murakami, H., Bessinger, K., Hellmann, J., & Murakami, S. (2008). Manipulation of serotonin signal suppresses early phase of behavioral aging in Caenorhabditis elegans: Neurobiology of Aging Vol 29(7) Jul 2008, 1093-1100.
- Pechova, H., & Foltan, P. (2008). The parasitic nematode Phasmarhabditis hermaphrodita defends its slug host from being predated or scavenged by manipulating host spatial behaviour: Behavioural Processes Vol 78(3) Jul 2008, 416-420.
- Petrascheck, M., Ye, X., & Buck, L. B. (2007). An antidepressant that extends lifespan in adult Caenorhabditis elegans: Nature Vol 450(7169) Nov 2007, 553-555.
- Poyraz, B. C., Ekmen, S. S., & Doksat, M. K. (2005). An interesting case of delusional parasitosis: Yeni Symposium: psikiyatri, noroloji ve davranis bilimleri dergisi Vol 43(3) Jun 2005, 114-117.
- Prahlad, V., Pilgrim, D., & Goodwin, E. B. (2003). Roles for Mating and Environment in C. elegans Sex Determination: Science Vol 302(5647) Nov 2003, 1046-1049.
- Puhl, J. G., & Mesce, K. A. (2008). Dopamine activates the motor pattern for crawling in the medicinal leech: Journal of Neuroscience Vol 28(16) Apr 2008, 4192-4200.
- Remy, J.-J., & Hobert, O. (2005). An Interneuronal Chemoreceptor Required for Olfactory Imprinting in C. elegans: Science Vol 309(5735) Jul 2005, 787-790.
- Riedl, C. A. L., & Sokolowski, M. B. (2004). Behavioral Genetics: Guanylyl Cyclase Prompts Worms to Party: Current Biology Vol 14(16) Aug 2004, R657-R658.
- Rose, J. K., & Rankin, C. H. (2001). Analyses of habituation in Caenorhabditis elegans: Learning & Memory Vol 8(2) Mar-Apr 2001, 63-69.
- Rose, J. K., & Rankin, C. H. (2001). Behavioral, neural circuit, and genetic analyses of habituation in C. elegans. New York, NY: Psychology Press.
- Sanchez, M. I., Ponton, F., Misse, D., Hughes, D. P., & Thomas, F. (2008). Hairworm response to notonectid attacks: Animal Behaviour Vol 75(3) Mar 2008, 823-826.
- Sehadova, H., Markova, E. P., Sehnal, F., & Takeda, M. (2004). Distribution of Circadian Clock-Related Proteins in the Cephalic Nervous System of the Silkworm, Bombyx mori: Journal of Biological Rhythms Vol 19(6) Dec 2004, 466-482.
- Steidl, S., Rose, J. K., & Rankin, C. H. (2003). Stages of Memory in the Nematode Caenorhabditis elegans: Behavioral and Cognitive Neuroscience Reviews Vol 2(1) Mar 2003, 3-14.
- Traore, S., Enyong, P., Mandiangu, M. L., Kayembe, D., Zoure, H., Noma, M., et al. (2006). Vector capacities of Similium damsnosum s.l and risk for Onchocerca volvulus' transmission in Inga (Democratic Republic of Congo): Cahiers D'Etudes et De Recherche Francophone/ Sante Vol 16(2) Apr-Jun 2006, 77-82.
- Wakabayashi, T., Kitagawa, I., & Shingai, R. (2004). Neurons regulating the duration of forward locomotion in Caenorhabditis elegans: Neuroscience Research Vol 50(1) Sep 2004, 103-111.
- Williams-Blangero, S., Subedi, J., Upadhayay, R. P., Manral, D. B., Khadka, K., Jirel, S., et al. (1998). Attitudes towards helminthic infection in the Jirel population of eastern Nepal: Social Science & Medicine Vol 47(3) Aug 1998, 371-379.
- Ye, H., Ye, B., & Wang, D. (2008). Trace administration of vitamin E can retrieve and prevent UV-irradiation- and metal exposure-induced memory deficits in nematode Caenorhabditis elegans: Neurobiology of Learning and Memory Vol 90(1) Jul 2008, 10-18.
- Zhao, B., Khare, P., Feldman, L., & Dent, J. A. (2003). Reversal Frequency in Caenorhabditis elegans Represents an Integrated Response to the State of the Animal and Its Environment: Journal of Neuroscience Vol 23(12) Jun 2003, 5319-5328.
- Zheng, M., Friesen, W. O., & Iwasaki, T. (2007). Systems-level modeling of neuronal circuits for leech swimming: Journal of Computational Neuroscience Vol 22(1) Feb 2007, 21-38.
Additional material[edit | edit source]
Books[edit | edit source]
Papers[edit | edit source]
Dissertations[edit | edit source]
- Beck, C. D. O. B. (1996). Factors affecting long-term habituation in Caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Clark, D. A. (2008). Biophysical analysis of thermotactic behavior in Caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Ghosh, R. (2007). Neuronal and genetic basis of a novel episodic behavior in caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Huang, K. M. (2008). Tracking and analysis of Caenorhabditis elegans behavior using machine vision. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Kleemann, G. A. (2008). The endocrine regulation of male exploratory behavior in the nematode Caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Larocque, R. (2007). Randomized controlled trial of mebendazole plus iron supplementation versus placebo plus iron supplementation during pregnancy. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Pinkston, J. M. (2008). The link between aging and tumor growth in Caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Qian, H. (2008). Nematode nicotinic acetylcholine receptors: A single-channel study in Ascaris suum and Caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Ray, P. (2007). The NK-2 family homeobox gene ceh-28 controls M4 neuronal function in caenorhabditis elegans. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Zhang, M. (2008). Functional characterization and theoretical modeling of the Caenorhabditis elegans egg-laying circuit. Dissertation Abstracts International: Section B: The Sciences and Engineering.
- Zheng, M. (2007). Modeling of CPG-based control mechanisms for leech swimming. Dissertation Abstracts International: Section B: The Sciences and Engineering.
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