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101-515: Leeches are segmented parasitic or predatory worms that comprise the subclass Hirudinea within the phylum Annelida . They are closely related to the oligochaetes , which include the earthworm , and like them have soft, muscular segmented bodies that can lengthen and contract. Both groups are hermaphrodites and have a clitellum , but leeches typically differ from the oligochaetes in having suckers at both ends and ring markings that do not correspond with their internal segmentation. The body
202-438: A holoparasite such as Cuscuta derives all of its nutrients from another plant. Parasitic plants make up about one per cent of angiosperms and are in almost every biome in the world. All these plants have modified roots, haustoria , which penetrate the host plants, connecting them to the conductive system—either the xylem , the phloem , or both. This provides them with the ability to extract water and nutrients from
303-574: A blood meal. Some marine species however remain attached until it is time to reproduce. If present in great numbers on a host, these can be debilitating, and in extreme cases, cause death. Leeches are unusual in that they do not produce certain digestive enzymes such as amylases , lipases or endopeptidases . A deficiency of these enzymes and of B complex vitamins is compensated for by enzymes and vitamins produced by endosymbiotic microflora. In Hirudo medicinalis , these supplementary factors are produced by an obligatory mutualistic relationship with
404-511: A cause of gastroenteritis , is spread by the fecal–oral route from animals, or by eating insufficiently cooked poultry , or by contaminated water. Haemophilus influenzae , an agent of bacterial meningitis and respiratory tract infections such as influenza and bronchitis , is transmitted by droplet contact. Treponema pallidum , the cause of syphilis , is spread by sexual activity . Viruses are obligate intracellular parasites, characterised by extremely limited biological function, to
505-627: A faster rate than their hosts. Classic examples include interactions between vertebrate hosts and tapeworms , flukes , and those between the malaria-causing Plasmodium species, and fleas . Parasites reduce host fitness by general or specialised pathology , that ranges from parasitic castration to modification of host behaviour . Parasites increase their own fitness by exploiting hosts for resources necessary for their survival, in particular by feeding on them and by using intermediate (secondary) hosts to assist in their transmission from one definitive (primary) host to another. Although parasitism
606-458: A feeling of faintness or dizziness, and difficulty in breathing. An externally attached leech will detach and fall off on its own accord when it is satiated on blood, which may take from twenty minutes to a few hours; bleeding from the wound may continue for some time. Internal attachments, such as inside the nose, are more likely to require medical intervention. Bacteria, viruses, and protozoan parasites from previous blood sources can survive within
707-595: A hormone or by diverting nutrients. For example, the trematode Zoogonus lasius , whose sporocysts lack mouths, castrates the intertidal marine snail Tritia obsoleta chemically, developing in its gonad and killing its reproductive cells. Directly transmitted parasites, not requiring a vector to reach their hosts, include such parasites of terrestrial vertebrates as lice and mites; marine parasites such as copepods and cyamid amphipods; monogeneans ; and many species of nematodes, fungi, protozoans, bacteria, and viruses. Whether endoparasites or ectoparasites, each has
808-414: A jaw many have a protrusible proboscis , which for most of the time they keep retracted into the mouth. Such leeches are often ambush predators that lie in wait until they can strike prey with the proboscises in a spear-like fashion. Predatory leeches feed on small invertebrates such as snails, earthworms and insect larvae. The prey is usually sucked in and swallowed whole. Some Rhynchobdellida however suck
909-411: A leech for months, so leeches could potentially act as vectors of pathogens. Nevertheless, only a few cases of leeches transmitting pathogens to humans have been reported. Leech saliva is commonly believed to contain anaesthetic compounds to numb the bite area, but some authorities disagree. Although morphine -like substances have been found in leeches, they have been found in the neural tissues , not
1010-437: A loose connective tissue composed of clusters of cells of mesodermal origin. The remaining body cavity has been reduced to four slender longitudinal channels. Typically, the body is dorso-ventrally flattened and tapers at both ends. Longitudinal and circular muscles in the body wall are supplemented by diagonal muscles, giving the leech the ability to adopt a large range of body shapes and show great flexibility. Most leeches have
1111-415: A mammal species hosts four species of nematode, two of trematodes, and two of cestodes. Humans have 342 species of helminth parasites, and 70 species of protozoan parasites. Some three-quarters of the links in food webs include a parasite, important in regulating host numbers. Perhaps 40 per cent of described species are parasitic. Erpobdelliformes See text The Erpobdelliformes are one of
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#17327910163041212-404: A modification of the locomotion by peristalsis , self-propulsion by alternately contracting and lengthening parts of the body, seen in other annelids such as earthworms. They use their posterior and anterior suckers (one on each end of the body) to enable them to progress by looping or inching along, in the manner of geometer moth caterpillars. The posterior end is attached to the substrate, and
1313-421: A nerve ganglion , and between them contain two reproductive organs, a single female gonopore and nine pairs of testes . The last seven segments contain the posterior brain and are fused to form the animal's tail sucker. The septa that separates the body segments—and the mesenteries which in turn separates each segment into a left and right half—in the majority of annelids, have been lost in leeches except for
1414-836: A parasite employs to identify and approach a potential host are known as "host cues". Such cues can include, for example, vibration, exhaled carbon dioxide , skin odours, visual and heat signatures, and moisture. Parasitic plants can use, for example, light, host physiochemistry, and volatiles to recognize potential hosts. There are six major parasitic strategies , namely parasitic castration ; directly transmitted parasitism; trophically -transmitted parasitism; vector -transmitted parasitism; parasitoidism ; and micropredation. These apply to parasites whose hosts are plants as well as animals. These strategies represent adaptive peaks ; intermediate strategies are possible, but organisms in many different groups have consistently converged on these six, which are evolutionarily stable. A perspective on
1515-635: A parasitic alien species. First used in English in 1539, the word parasite comes from the Medieval French parasite , from the Latinised form parasitus , from Ancient Greek παράσιτος (parasitos) 'one who eats at the table of another' in turn from παρά (para) 'beside, by' and σῖτος (sitos) 'wheat, food'. The related term parasitism appears in English from 1611. Parasitism
1616-432: A phenomenon termed the biotrophy-necrotrophy switch . Pathogenic fungi are well-known causative agents of diseases on animals as well as humans. Fungal infections ( mycosis ) are estimated to kill 1.6 million people each year. One example of a potent fungal animal pathogen are Microsporidia - obligate intracellular parasitic fungi that largely affect insects, but may also affect vertebrates including humans, causing
1717-538: A predator, the European sparrowhawk , giving her time to lay her eggs in the host's nest unobserved. Host species often combat parasitic egg mimicry through egg polymorphism , having two or more egg phenotypes within a single population of a species. Multiple phenotypes in host eggs decrease the probability of a parasitic species accurately "matching" their eggs to host eggs. In kleptoparasitism (from Greek κλέπτης ( kleptēs ), "thief"), parasites steal food gathered by
1818-526: A relatively large, toothless mouth to ingest insect larvae, molluscs, and other annelid worms, which are swallowed whole. In turn, leeches are prey to fish, birds, and invertebrates. The name for the subclass, Hirudinea, comes from the Latin hirudo ( genitive hirudinis ), a leech; the element -bdella found in many leech group names is from the Greek βδέλλα bdella , also meaning leech. The name Les hirudinées
1919-573: A single host-species. Within that species, most individuals are free or almost free of parasites, while a minority carry a large number of parasites; this is known as an aggregated distribution . Trophically -transmitted parasites are transmitted by being eaten by a host. They include trematodes (all except schistosomes ), cestodes , acanthocephalans , pentastomids , many roundworms , and many protozoa such as Toxoplasma . They have complex life cycles involving hosts of two or more species. In their juvenile stages they infect and often encyst in
2020-423: A sucker at both the anterior (front) and posterior (back) ends, but some primitive leeches have a single sucker at the back. Like most annelids, with a few exceptions like Sipuncula , Echiura and Diurodrilus , the leech is a segmented animal, but unlike other annelids, the segmentation is masked by secondary external ring markings ( annuli ). The number of annulations varies, both between different regions of
2121-430: A suitable fungus soon after germinating. Parasitic fungi derive some or all of their nutritional requirements from plants, other fungi, or animals. Plant pathogenic fungi are classified into three categories depending on their mode of nutrition: biotrophs, hemibiotrophs and necrotrophs. Biotrophic fungi derive nutrients from living plant cells, and during the course of infection they colonise their plant host in such
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#17327910163042222-1047: A variety of methods to infect animal hosts, including physical contact, the fecal–oral route , free-living infectious stages, and vectors, suiting their differing hosts, life cycles, and ecological contexts. Examples to illustrate some of the many possible combinations are given in the table. social behaviour (grooming) Among the many variations on parasitic strategies are hyperparasitism, social parasitism, brood parasitism, kleptoparasitism, sexual parasitism, and adelphoparasitism. Hyperparasites feed on another parasite, as exemplified by protozoa living in helminth parasites, or facultative or obligate parasitoids whose hosts are either conventional parasites or parasitoids. Levels of parasitism beyond secondary also occur, especially among facultative parasitoids. In oak gall systems, there can be up to five levels of parasitism. Hyperparasites can control their hosts' populations, and are used for this purpose in agriculture and to some extent in medicine . The controlling effects can be seen in
2323-469: A variety of routes. To give a few examples, Bacillus anthracis , the cause of anthrax , is spread by contact with infected domestic animals ; its spores , which can survive for years outside the body, can enter a host through an abrasion or may be inhaled. Borrelia , the cause of Lyme disease and relapsing fever , is transmitted by vectors, ticks of the genus Ixodes , from the diseases' reservoirs in animals such as deer . Campylobacter jejuni ,
2424-474: A way as to keep it alive for a maximally long time. One well-known example of a biotrophic pathogen is Ustilago maydis , causative agent of the corn smut disease. Necrotrophic pathogens on the other hand, kill host cells and feed saprophytically , an example being the root-colonising honey fungi in the genus Armillaria . Hemibiotrophic pathogens begin their colonising their hosts as biotrophs, and subsequently killing off host cells and feeding as necrotrophs,
2525-544: Is a close relationship between species , where one organism, the parasite, lives on or inside another organism, the host , causing it some harm, and is adapted structurally to this way of life. The entomologist E. O. Wilson characterised parasites as "predators that eat prey in units of less than one". Parasites include single-celled protozoans such as the agents of malaria , sleeping sickness , and amoebic dysentery ; animals such as hookworms , lice , mosquitoes , and vampire bats ; fungi such as honey fungus and
2626-563: Is a kind of symbiosis , a close and persistent long-term biological interaction between a parasite and its host. Unlike saprotrophs , parasites feed on living hosts, though some parasitic fungi, for instance, may continue to feed on hosts they have killed. Unlike commensalism and mutualism , the parasitic relationship harms the host, either feeding on it or, as in the case of intestinal parasites, consuming some of its food. Because parasites interact with other species, they can readily act as vectors of pathogens, causing disease . Predation
2727-479: Is a small protein, hirudin. It is widely used as an anticoagulant drug to treat blood-clotting disorders, and manufactured by recombinant DNA technology. In 2012 and 2018, Ida Schnell and colleagues trialled the use of Haemadipsa leeches to gather data on the biodiversity of their mammalian hosts in the tropical rainforest of Vietnam, where it is hard to obtain reliable data on rare and cryptic mammals. They showed that mammal mitochondrial DNA , amplified by
2828-675: Is aggregated. Coinfection by multiple parasites is common. Autoinfection , where (by exception) the whole of the parasite's life cycle takes place in a single primary host, can sometimes occur in helminths such as Strongyloides stercoralis . Vector-transmitted parasites rely on a third party, an intermediate host, where the parasite does not reproduce sexually, to carry them from one definitive host to another. These parasites are microorganisms, namely protozoa , bacteria , or viruses , often intracellular pathogens (disease-causers). Their vectors are mostly hematophagic arthropods such as fleas, lice, ticks, and mosquitoes. For example,
2929-463: Is based on molecular analysis (2019) of DNA sequences. Both the former classes " Polychaeta " (bristly marine worms) and " Oligochaeta " (including the earthworms) are paraphyletic : in each case the complete groups ( clades ) would include all the other groups shown below them in the tree. The Branchiobdellida are sister to the leech clade Hirudinida, which approximately corresponds to the traditional subclass Hirudinea. The main subdivision of leeches
3030-443: Is by definition not a symbiosis, as the interaction is brief, but the entomologist E. O. Wilson has characterised parasites as "predators that eat prey in units of less than one". Within that scope are many possible strategies. Taxonomists classify parasites in a variety of overlapping schemes, based on their interactions with their hosts and on their life cycles , which can be complex. An obligate parasite depends completely on
3131-645: Is found in the ant Tetramorium inquilinum , an obligate parasite which lives exclusively on the backs of other Tetramorium ants. A mechanism for the evolution of social parasitism was first proposed by Carlo Emery in 1909. Now known as " Emery's rule ", it states that social parasites tend to be closely related to their hosts, often being in the same genus. Intraspecific social parasitism occurs in parasitic nursing, where some individual young take milk from unrelated females. In wedge-capped capuchins , higher ranking females sometimes take milk from low ranking females without any reciprocation. In brood parasitism ,
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3232-770: Is into the Rhynchobdellida and the Arhynchobdellida, though the Acanthobdella are sister to the clade that contains these two groups. " Polychaeta " (exc. "Oligochaeta") [REDACTED] " Oligochaeta " (exc. Lumbriculidae) [REDACTED] Lumbriculidae (blackworms) [REDACTED] [REDACTED] Acanthobdella [REDACTED] Erpobdelliformes [REDACTED] Hirudiniformes [REDACTED] Glossiphoniidae [REDACTED] Piscicolidae [REDACTED] Ozobranchidae [REDACTED] The most ancient annelid group consists of
3333-440: Is muscular and relatively solid; the coelom , the spacious body cavity found in other annelids, is reduced to small channels. The majority of leeches live in freshwater habitats, while some species can be found in terrestrial or marine environments. The best-known species, such as the medicinal leech, Hirudo medicinalis , are hematophagous , attaching themselves to a host with a sucker and feeding on blood, having first secreted
3434-585: Is often unambiguous, it is part of a spectrum of interactions between species , grading via parasitoidism into predation, through evolution into mutualism , and in some fungi, shading into being saprophytic . Human knowledge of parasites such as roundworms and tapeworms dates back to ancient Egypt , Greece , and Rome . In early modern times, Antonie van Leeuwenhoek observed Giardia lamblia with his microscope in 1681, while Francesco Redi described internal and external parasites including sheep liver fluke and ticks . Modern parasitology developed in
3535-435: Is pushed by one through the integument of the other, usually into the clitellar region. The sperm is liberated and passes to the ovisacs, either through the coelomic channels or interstitially through specialist "target tissue" pathways. Some time after copulation, the small, relatively yolkless eggs are laid. In most species, an albumin -filled cocoon is secreted by the clitellum and receives one or more eggs as it passes over
3636-419: Is seen in some species of anglerfish , such as Ceratias holboelli , where the males are reduced to tiny sexual parasites , wholly dependent on females of their own species for survival, permanently attached below the female's body, and unable to fend for themselves. The female nourishes the male and protects him from predators, while the male gives nothing back except the sperm that the female needs to produce
3737-420: Is so slow. A leech's nervous system is formed of a few large nerve cells . Their large size makes leeches convenient as model organisms for the study of invertebrate nervous systems. The main nerve centre consists of the cerebral ganglion above the gut and another ganglion beneath it, with connecting nerves forming a ring around the pharynx a little way behind the mouth. A nerve cord runs backwards from this in
3838-422: Is sometimes identified as leech, but assignment of fossil is still putative and contentious, and the animal was also alternatively interpreted as a member of Cycloneuralia . Leeches show a remarkable similarity to each other in morphology, very different from typical annelids which are cylindrical with a fluid-filled space, the coelom (body cavity). In leeches, most of the coelom is filled with botryoidal tissue,
3939-469: Is then carried to a nest, sometimes alongside other prey if it is not large enough to support a parasitoid throughout its development. An egg is laid on top of the prey and the nest is then sealed. The parasitoid develops rapidly through its larval and pupal stages, feeding on the provisions left for it. Koinobiont parasitoids, which include flies as well as wasps, lay their eggs inside young hosts, usually larvae. These are allowed to go on growing, so
4040-420: Is used as an anticoagulant drug to treat blood-clotting disorders. The leech appears in the biblical Book of Proverbs as an archetype of insatiable greed . The term "leech" is used to characterise a person who takes without giving, living at the expense of others. Some 680 species of leech have been described, of which around 100 are marine, 480 freshwater and the remainder terrestrial. Among Euhirudinea ,
4141-407: The horse leech could drive elephants mad by climbing up inside their trunks to drink blood. Pliny also noted the medicinal use of leeches in ancient Rome , stating that they were often used for gout , and that patients became addicted to the treatment. In Old English , lǣce was the name for a physician as well as for the animal, though the words had different origins, and lǣcecraft , leechcraft,
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4242-648: The polymerase chain reaction , can be identified from a leech's blood meal for at least four months after feeding. They detected Annamite striped rabbit , small-toothed ferret-badger , Truong Son muntjac , and serow in this way. Exposure to synthetic estrogen as used in contraceptive medicines, which may enter freshwater ecosystems from municipal wastewater , can affect leeches' reproductive systems. Although not as sensitive to these compounds as fish, leeches showed physiological changes after exposure, including longer sperm sacs and vaginal bulbs , and decreased epididymis weight. Parasitism Parasitism
4343-505: The snubnosed eel is probably a facultative endoparasite (i.e., it is semiparasitic) that opportunistically burrows into and eats sick and dying fish. Plant-eating insects such as scale insects , aphids , and caterpillars closely resemble ectoparasites, attacking much larger plants; they serve as vectors of bacteria, fungi and viruses which cause plant diseases . As female scale insects cannot move, they are obligate parasites, permanently attached to their hosts. The sensory inputs that
4444-511: The 19th century. In human culture, parasitism has negative connotations. These were exploited to satirical effect in Jonathan Swift 's 1733 poem "On Poetry: A Rhapsody", comparing poets to hyperparasitical "vermin". In fiction, Bram Stoker 's 1897 Gothic horror novel Dracula and its many later adaptations featured a blood-drinking parasite. Ridley Scott 's 1979 film Alien was one of many works of science fiction to feature
4545-458: The agents of ringworm ; and plants such as mistletoe , dodder , and the broomrapes . There are six major parasitic strategies of exploitation of animal hosts, namely parasitic castration , directly transmitted parasitism (by contact), trophically-transmitted parasitism (by being eaten), vector-transmitted parasitism, parasitoidism , and micropredation. One major axis of classification concerns invasiveness: an endoparasite lives inside
4646-711: The air or soil given off by host shoots or roots , respectively. About 4,500 species of parasitic plant in approximately 20 families of flowering plants are known. Species within the Orobanchaceae (broomrapes) are among the most economically destructive of all plants. Species of Striga (witchweeds) are estimated to cost billions of dollars a year in crop yield loss, infesting over 50 million hectares of cultivated land within Sub-Saharan Africa alone. Striga infects both grasses and grains, including corn , rice , and sorghum , which are among
4747-480: The anterior end is projected forward peristaltically by the circular muscles until it touches down, as far as it can reach, and the anterior end is attached. Then the posterior end is released, pulled forward by the longitudinal muscles, and reattached; then the anterior end is released, and the cycle repeats. Leeches explore their environment with head movements and body waving. The Hirudinidae and Erpobdellidae can swim rapidly with up-and-down or sideways undulations of
4848-528: The aquatic Hirudinidae have a wider global range; both of these feed largely on mammals, including humans. A distinctive family is the Piscicolidae , marine or freshwater ectoparasites chiefly of fish, with cylindrical bodies and usually well-marked, bell-shaped, anterior suckers. Not all leeches feed on blood; the Erpobdelliformes , freshwater or amphibious, are carnivorous and equipped with
4949-561: The bacterial species, Aeromonas veronii . Non-bloodsucking leeches, such as Erpobdella octoculata , are host to more bacterial symbionts. In addition, leeches produce intestinal exopeptidases which remove amino acids from the long protein molecules one by one, possibly aided by proteases from endosymbiotic bacteria in the hindgut. This evolutionary choice of exopeptic digestion in Hirudinea distinguishes these carnivorous clitellates from oligochaetes, and may explain why digestion in leeches
5050-433: The body and between species. In one species, the body surface is divided into 102 annuli . All leech species, however, have 32 segments, called somites, (34 if two head segments, which have different organization, are counted). Of these segments, the first five are designated as the head and include the anterior brain, several ocelli (eyespots) dorsally and the sucker ventrally. The following 21 mid-body segments each contain
5151-476: The body; the Glossiphoniidae in contrast are poor swimmers and curl up and fall to the sediment below when disturbed. Leech bites are generally alarming rather than dangerous, though a small percentage of people have severe allergic or anaphylactic reactions and require urgent medical care. Symptoms of these reactions include red blotches or an itchy rash over the body, swelling around the lips or eyes,
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#17327910163045252-554: The chances of finding a host. Leeches live in damp surroundings and in general respire through their body wall. The exception to this is in the Piscicolidae, where branching or leaf-like lateral outgrowths from the body wall form gills . Some rhynchobdellid leeches have an extracellular haemoglobin pigment, but this only provides for about half of the leech's oxygen transportation needs, the rest occurring by diffusion. Leeches move using their longitudinal and circular muscles in
5353-435: The cocoon to the substrate and covering it with their ventral surface, or by securing the cocoon to their ventral surface, and even carrying the newly hatched young to their first meal. When breeding, most marine leeches leave their hosts and become free-living in estuaries. Here they produce their cocoons, after which the adults of most species die. When the eggs hatch, the juveniles seek out potential hosts when these approach
5454-864: The deer tick Ixodes scapularis acts as a vector for diseases including Lyme disease , babesiosis , and anaplasmosis . Protozoan endoparasites, such as the malarial parasites in the genus Plasmodium and sleeping-sickness parasites in the genus Trypanosoma , have infective stages in the host's blood which are transported to new hosts by biting insects. Parasitoids are insects which sooner or later kill their hosts, placing their relationship close to predation. Most parasitoids are parasitoid wasps or other hymenopterans ; others include dipterans such as phorid flies . They can be divided into two groups, idiobionts and koinobionts, differing in their treatment of their hosts. Idiobiont parasitoids sting their often-large prey on capture, either killing them outright or paralysing them immediately. The immobilised prey
5555-459: The edges of ponds, lakes and slow-moving streams; very few species tolerate fast-flowing water. In their preferred habitats, they may occur in very high densities; in a favourable environment with water high in organic pollutants, over 10,000 individuals were recorded per square metre (over 930 per square foot) under rocks in Illinois . Some species aestivate during droughts, burying themselves in
5656-584: The eggs being brooded by the parent. In terrestrial species, the cocoon is often concealed under a log, in a crevice or buried in damp soil. Almost seven hundred species of leech are currently recognised, of which some hundred are marine, ninety terrestrial and the remainder freshwater. Leeches have been used in medicine from ancient times until the 19th century to draw blood from patients. In modern times, leeches find medical use in treatment of joint diseases such as epicondylitis and osteoarthritis, extremity vein diseases, and in microsurgery , while hirudin
5757-409: The energy that would have gone into reproduction into host and parasite growth, sometimes causing gigantism in the host. The host's other systems remain intact, allowing it to survive and to sustain the parasite. Parasitic crustaceans such as those in the specialised barnacle genus Sacculina specifically cause damage to the gonads of their many species of host crabs . In the case of Sacculina ,
5858-491: The evolutionary options can be gained by considering four key questions: the effect on the fitness of a parasite's hosts; the number of hosts they have per life stage; whether the host is prevented from reproducing; and whether the effect depends on intensity (number of parasites per host). From this analysis, the major evolutionary strategies of parasitism emerge, alongside predation. Parasitic castrators partly or completely destroy their host's ability to reproduce, diverting
5959-444: The family Cuculidae , over 40% of cuckoo species are obligate brood parasites, while others are either facultative brood parasites or provide parental care. The eggs of some brood parasites mimic those of their hosts, while some cowbird eggs have tough shells, making them hard for the hosts to kill by piercing, both mechanisms implying selection by the hosts against parasitic eggs. The adult female European cuckoo further mimics
6060-492: The female gonopore. In the case of the North American Erpobdella punctata , the clutch size is about five eggs, and some ten cocoons are produced. Each cocoon is fixed to a submerged object, or in the case of terrestrial leeches, deposited under a stone or buried in damp soil. The cocoon of Hemibdella soleae is attached to a suitable fish host . The glossiphoniids brood their eggs, either by attaching
6161-700: The free-living polychaetes that evolved in the Cambrian period, being plentiful in the Burgess Shale about 500 million years ago. Oligochaetes evolved from polychaetes and the leeches branched off from the oligochaetes. The oldest leech fossils are from the middle Permian period around 266 million years ago, there is also unpublished study about possible leech from Virgilian (Late Carboniferous ) of New Mexico . Although fossil with external ring markings found from Silurian strata in Wisconsin
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#17327910163046262-407: The front of the body. There are also sensory papillae arranged in a lateral row in one annulation of each segment. Each papilla contains many sensory cells. Some rhynchobdellids have the ability to change colour dramatically by moving pigment in chromatophore cells; this process is under the control of the nervous system but its function is unclear as the change in hue seems unrelated to the colour of
6363-408: The front of the mouth, and have three blades set at an angle to each other. In feeding, these slice their way through the skin of the host, leaving a Y-shaped incision. Behind the blades is the mouth, located ventrally at the anterior end of the body. It leads successively into the pharynx , a short oesophagus, a crop (in some species), a stomach and a hindgut, which ends at an anus located just above
6464-424: The host and parasitoid develop together for an extended period, ending when the parasitoids emerge as adults, leaving the prey dead, eaten from inside. Some koinobionts regulate their host's development, for example preventing it from pupating or making it moult whenever the parasitoid is ready to moult. They may do this by producing hormones that mimic the host's moulting hormones ( ecdysteroids ), or by regulating
6565-442: The host to complete its life cycle, while a facultative parasite does not. Parasite life cycles involving only one host are called "direct"; those with a definitive host (where the parasite reproduces sexually) and at least one intermediate host are called "indirect". An endoparasite lives inside the host's body; an ectoparasite lives outside, on the host's surface. Mesoparasites—like some copepods , for example—enter an opening in
6666-422: The host's body and remain partly embedded there. Some parasites can be generalists, feeding on a wide range of hosts, but many parasites, and the majority of protozoans and helminths that parasitise animals, are specialists and extremely host-specific. An early basic, functional division of parasites distinguished microparasites and macroparasites. These each had a mathematical model assigned in order to analyse
6767-453: The host's body; an ectoparasite lives outside, on the host's surface. Like predation, parasitism is a type of consumer–resource interaction , but unlike predators , parasites, with the exception of parasitoids, are much smaller than their hosts, do not kill them, and often live in or on their hosts for an extended period. Parasites of animals are highly specialised , each parasite species living on one given animal species, and reproduce at
6868-656: The host's endocrine system. A micropredator attacks more than one host, reducing each host's fitness by at least a small amount, and is only in contact with any one host intermittently. This behavior makes micropredators suitable as vectors, as they can pass smaller parasites from one host to another. Most micropredators are hematophagic , feeding on blood. They include annelids such as leeches , crustaceans such as branchiurans and gnathiid isopods, various dipterans such as mosquitoes and tsetse flies , other arthropods such as fleas and ticks, vertebrates such as lampreys , and mammals such as vampire bats . Parasites use
6969-425: The host. A parasitic plant is classified depending on where it latches onto the host, either the stem or the root, and the amount of nutrients it requires. Since holoparasites have no chlorophyll and therefore cannot make food for themselves by photosynthesis , they are always obligate parasites, deriving all their food from their hosts. Some parasitic plants can locate their host plants by detecting chemicals in
7070-477: The host. The parasitism is often on close relatives, whether within the same species or between species in the same genus or family. For instance, the many lineages of cuckoo bees lay their eggs in the nest cells of other bees in the same family. Kleptoparasitism is uncommon generally but conspicuous in birds; some such as skuas are specialised in pirating food from other seabirds, relentlessly chasing them down until they disgorge their catch. A unique approach
7171-423: The hosts suffer increased parental investment and energy expenditure to feed parasitic young, which are commonly larger than host young. The growth rate of host nestlings is slowed, reducing the host's fitness. Brood parasites include birds in different families such as cowbirds , whydahs , cuckoos , and black-headed ducks . These do not build nests of their own, but leave their eggs in nests of other species . In
7272-472: The intermediate host. When the intermediate-host animal is eaten by a predator, the definitive host, the parasite survives the digestion process and matures into an adult; some live as intestinal parasites . Many trophically transmitted parasites modify the behaviour of their intermediate hosts, increasing their chances of being eaten by a predator. As with directly transmitted parasites, the distribution of trophically transmitted parasites among host individuals
7373-471: The intestinal infection microsporidiosis . Protozoa such as Plasmodium , Trypanosoma , and Entamoeba are endoparasitic. They cause serious diseases in vertebrates including humans—in these examples, malaria, sleeping sickness, and amoebic dysentery —and have complex life cycles. Many bacteria are parasitic, though they are more generally thought of as pathogens causing disease. Parasitic bacteria are extremely diverse, and infect their hosts by
7474-441: The large blue butterfly, Phengaris arion , its larvae employing ant mimicry to parasitise certain ants, Bombus bohemicus , a bumblebee which invades the hives of other bees and takes over reproduction while their young are raised by host workers, and Melipona scutellaris , a eusocial bee whose virgin queens escape killer workers and invade another colony without a queen. An extreme example of interspecific social parasitism
7575-579: The largest group is the parasitoid wasps in the Hymenoptera. The phyla and classes with the largest numbers of parasitic species are listed in the table. Numbers are conservative minimum estimates. The columns for Endo- and Ecto-parasitism refer to the definitive host, as documented in the Vertebrate and Invertebrate columns. A hemiparasite or partial parasite such as mistletoe derives some of its nutrients from another living plant, whereas
7676-537: The marine worm Bonellia viridis has a similar reproductive strategy, although the larvae are planktonic. Examples of the major variant strategies are illustrated. Parasitism has an extremely wide taxonomic range, including animals, plants, fungi, protozoans, bacteria, and viruses. Parasitism is widespread in the animal kingdom, and has evolved independently from free-living forms hundreds of times. Many types of helminth including flukes and cestodes have complete life cycles involving two or more hosts. By far
7777-406: The mid-region of the leech. From these, ducts typically lead to a urinary bladder , which empties to the outside at a nephridiopore . Leeches are hermaphrodites, with the male reproductive organs , the testes , maturing first and the ovaries later. In hirudinids, a pair will line up with the clitellar regions in contact, with the anterior end of one leech pointing towards the posterior end of
7878-438: The modified coelom known as the haemocoelomic system, and the coelomic fluid, called the haemocoelomic fluid, has taken over the role as blood. The haemocoelomic channels run the full length of the body, the two main ones being on either side. Part of the lining epithelium consists of chloragogen cells which are used for the storage of nutrients and in excretion . There are 10 to 17 pairs of metanephridia (excretory organs) in
7979-407: The next generation. Adelphoparasitism, (from Greek ἀδελφός ( adelphós ), brother ), also known as sibling-parasitism, occurs where the host species is closely related to the parasite, often in the same family or genus. In the citrus blackfly parasitoid, Encarsia perplexa , unmated females may lay haploid eggs in the fully developed larvae of their own species, producing male offspring, while
8080-827: The nineteenth century, demand for leeches was sufficient for hirudiculture, the farming of leeches, to become commercially viable. Leech usage declined with the demise of humoral theory, but made a small-scale comeback in the 1980s after years of decline, with the advent of microsurgery , where venous congestion can arise due to inefficient venous drainage. Leeches can reduce swelling in the tissues and promote healing, helping in particular to restore circulation after microsurgery to reattach body parts. Other clinical applications include varicose veins , muscle cramps, thrombophlebitis , and joint diseases such as epicondylitis and osteoarthritis . Leech secretions contain several bioactive substances with anti-inflammatory , anticoagulant and antimicrobial effects. One active component of leech saliva
8181-510: The other; this results in the male gonopore of one leech being in contact with the female gonopore of the other. The penis passes a spermatophore into the female gonopore and sperm is transferred to, and probably stored in, the vagina. Some jawless leeches (Rhynchobdellida) and proboscisless leeches (Arhynchobdellida) lack a penis, and in these, sperm is passed from one individual to another by hypodermic injection . The leeches intertwine and grasp each other with their suckers. A spermatophore
8282-427: The peptide hirudin to prevent the blood from clotting. The jaws used to pierce the skin are replaced in other species by a proboscis which is pushed into the skin. A minority of leech species are predatory, mostly preying on small invertebrates. The eggs are enclosed in a cocoon, which in aquatic species is usually attached to an underwater surface; members of one family, Glossiphoniidae , exhibit parental care, and
8383-417: The point where, while they are evidently able to infect all other organisms from bacteria and archaea to animals, plants and fungi, it is unclear whether they can themselves be described as living. They can be either RNA or DNA viruses consisting of a single or double strand of genetic material ( RNA or DNA , respectively), covered in a protein coat and sometimes a lipid envelope. They thus lack all
8484-535: The population movements of the host–parasite groupings. The microorganisms and viruses that can reproduce and complete their life cycle within the host are known as microparasites. Macroparasites are the multicellular organisms that reproduce and complete their life cycle outside of the host or on the host's body. Much of the thinking on types of parasitism has focused on terrestrial animal parasites of animals, such as helminths. Those in other environments and with other hosts often have analogous strategies. For example,
8585-456: The posterior sucker. The stomach may be a simple tube, but the crop, when present, is an enlarged part of the midgut with a number of pairs of ceca that store ingested blood. The leech secretes an anticoagulant, hirudin , in its saliva which prevents the blood from clotting before ingestion. A mature medicinal leech may feed only twice a year, taking months to digest a blood meal. The bodies of predatory leeches are similar, though instead of
8686-406: The primitive genus Acanthobdella , which still have some septa and mesenteries. The body wall consists of a cuticle , an epidermis and a thick layer of fibrous connective tissue in which are embedded the circular muscles, the diagonal muscles and the powerful longitudinal muscles. There are also dorso-ventral muscles. In leeches the original blood vascular system has been lost and replaced by
8787-490: The salivary tissues. They are used by the leeches in modulating their own immunocytes and not for anaesthetising bite areas on their hosts. Depending on the species and size, leech bites can be barely noticeable or they can be fairly painful. The medicinal leech Hirudo medicinalis , and some other species , have been used for clinical bloodletting for at least 2,500 years: Ayurvedic texts describe their use for bloodletting in ancient India. In ancient Greece , bloodletting
8888-482: The sediment, and can lose up to 90% of their bodyweight and still survive. Among the freshwater leeches are the Glossiphoniidae , dorso-ventrally flattened animals mostly parasitic on vertebrates such as turtles, and unique among annelids in both brooding their eggs and carrying their young on the underside of their bodies. The terrestrial Haemadipsidae are mostly native to the tropics and subtropics, while
8989-432: The shore. Leeches mostly have an annual or biannual life cycle. About three quarters of leech species are parasites that feed on the blood of a host, while the remainder are predators . Leeches either have a pharynx that they can protrude, commonly called a proboscis, or a pharynx that they cannot protrude, which in some groups is armed with jaws. In the proboscisless leeches, the jaws (if any) of Arhynchobdellids are at
9090-428: The soft tissues from their prey, making them intermediate between predators and blood-suckers. Blood-sucking leeches use their anterior suckers to connect to hosts for feeding. Once attached, they use a combination of mucus and suction to stay in place while they inject hirudin into the hosts' blood . In general, blood-feeding leeches are non host-specific, and do little harm to their host, dropping off after consuming
9191-417: The surroundings. Leeches can detect touch, vibration, movement of nearby objects, and chemicals secreted by their hosts; freshwater leeches crawl or swim towards a potential host standing in their pond within a few seconds. Species that feed on warm-blooded hosts move towards warmer objects. Many leeches avoid light, though some blood feeders move towards light when they are ready to feed, presumably increasing
9292-466: The testes of over two-thirds of their crab hosts degenerate sufficiently for these male crabs to develop female secondary sex characteristics such as broader abdomens, smaller claws and egg-grasping appendages. Various species of helminth castrate their hosts (such as insects and snails). This may happen directly, whether mechanically by feeding on their gonads, or by secreting a chemical that destroys reproductive cells; or indirectly, whether by secreting
9393-403: The tropics, however effectively cheat by taking carbon from a fungus rather than exchanging it for minerals. They have much reduced roots, as they do not need to absorb water from the soil; their stems are slender with few vascular bundles , and their leaves are reduced to small scales, as they do not photosynthesize. Their seeds are small and numerous, so they appear to rely on being infected by
9494-425: The true leeches, the smallest is about 1 cm ( 1 ⁄ 2 in) long, and the largest is the giant Amazonian leech, Haementeria ghilianii , which can reach 30 cm (12 in). Except for Antarctica, leeches are found throughout the world but are at their most abundant in temperate lakes and ponds in the northern hemisphere. The majority of freshwater leeches are found in the shallow, vegetated areas on
9595-506: The usual machinery of the cell such as enzymes , relying entirely on the host cell's ability to replicate DNA and synthesise proteins. Most viruses are bacteriophages , infecting bacteria. Parasitism is a major aspect of evolutionary ecology; for example, almost all free-living animals are host to at least one species of parasite. Vertebrates, the best-studied group, are hosts to between 75,000 and 300,000 species of helminths and an uncounted number of parasitic microorganisms. On average,
9696-407: The ventral coelomic channel, with 21 pairs of ganglia in segments six to 26. In segments 27 to 33, other paired ganglia fuse to form the caudal ganglion. Several sensory nerves connect directly to the cerebral ganglion; there are sensory and motor nerve cells connected to the ventral nerve cord ganglia in each segment. Leeches have between two and ten pigment spot ocelli , arranged in pairs towards
9797-589: The way that the CHV1 virus helps to control the damage that chestnut blight , Cryphonectria parasitica , does to American chestnut trees, and in the way that bacteriophages can limit bacterial infections. It is likely, though little researched, that most pathogenic microparasites have hyperparasites which may prove widely useful in both agriculture and medicine. Social parasites take advantage of interspecific interactions between members of eusocial animals such as ants , termites , and bumblebees . Examples include
9898-471: The world's most important food crops. Orobanche also threatens a wide range of other important crops, including peas , chickpeas , tomatoes , carrots , and varieties of cabbage . Yield loss from Orobanche can be total; despite extensive research, no method of control has been entirely successful. Many plants and fungi exchange carbon and nutrients in mutualistic mycorrhizal relationships. Some 400 species of myco-heterotrophic plants, mostly in
9999-541: Was given by Jean-Baptiste Lamarck in 1818. Leeches were traditionally divided into two infraclasses, the Acanthobdellidea (primitive leeches) and the Euhirudinea (true leeches). The Euhirudinea are divided into the proboscis-bearing Rhynchobdellida and the rest, including some jawed species, the " Arhynchobdellida ", without a proboscis. The phylogenetic tree of the leeches and their annelid relatives
10100-531: Was practised according to the theory of humours found in the Hippocratic Corpus of the fifth century BC, which maintained that health depended on a balance of the four humours: blood, phlegm , black bile and yellow bile . Bloodletting using leeches enabled physicians to restore balance if they considered blood was present in excess. Pliny the Elder reported in his Natural History that
10201-544: Was the art of healing. William Wordsworth 's 1802 poem " Resolution and Independence " describes one of the last of the leech-gatherers, people who travelled Britain catching leeches from the wild, and causing a sharp decline in their abundance, though they remain numerous in Romney Marsh . By 1863, British hospitals had switched to imported leeches, some seven million being imported to hospitals in London that year. In
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