Leech
Leech | |
---|---|
Hirudo medicinalis sucking blood | |
Helobdella sp. | |
Scientific classification | |
Domain: | Eukaryota |
Kingdom: | Animalia |
Phylum: | Annelida |
Class: | Clitellata |
Subclass: | Hirudinea Lamarck 1818 |
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 in having ring markings that do not correspond with their internal segmentation. The body is muscular and relatively solid, and 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, 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, 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 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.[1] The term "leech" is used to characterise a person who takes without giving, living at the expense of others.[2]
Diversity and phylogeny
Some 680 species of leech have been described, of which around 100 are marine, 480 freshwater and the remainder terrestrial.[4][5] Among Euhirudinea, 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,[4] 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 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 the sediment, and can lose up to 90% of their bodyweight and still survive.[6] 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.[7]
The terrestrial Haemadipsidae are mostly native to the tropics and subtropics,[8] while the aquatic Hirudinidae have a wider global range; both of these feed largely on mammals, including humans.[6] A distinctive family is the Piscicolidae, marine or freshwater ectoparasites chiefly of fish, with cylindrical bodies and usually well-marked, bell-shaped, anterior suckers.[9] Not all leeches feed on blood; the Erpobdelliformes, freshwater or amphibious, are carnivorous and equipped with a relatively large, toothless mouth to ingest insect larvae, molluscs, and other annelid worms, which are swallowed whole.[10] In turn, leeches are prey to fish, birds, and invertebrates.[11]
The name for the subclass, Hirudinea, comes from the Latin hirudo (
The
Annelida
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Evolution
The most ancient annelid group consists of 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.[16] The oldest leech fossils are from the middle Permian period around 266 million years ago,[17] there is also unpublished study about possible leech from Virgilian (Late Carboniferous) of New Mexico.[18] Although fossil with external ring markings found from Silurian strata in Wisconsin is sometimes identified as leech,[19][20] but assignment of fossil is still putative and contentious,[21][17] and the animal was also alternatively interpreted as a member of Cycloneuralia.[22][18]
Anatomy and physiology
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, a loose connective tissue composed of clusters of cells of mesodermal origin.[23] 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 a sucker at both the anterior (front) and posterior (back) ends, but some primitive leeches have a single sucker at the back.[24][25]
Like most annelids, with a few exceptions like
The body wall consists of a
Reproduction and development
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 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.[34]
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 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.[34]
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 the female gonopore.[34] In the case of the North American Erpobdella punctata, the clutch size is about five eggs, and some ten cocoons are produced.[35] 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.[34][36] The glossiphoniids brood their eggs, either by attaching 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.[37]
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 the shore.[37] Leeches mostly have an annual or biannual life cycle.[34]
Feeding and digestion
About three quarters of leech species are
In the proboscisless leeches, the jaws (if any) of Arhynchobdellids are at 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 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.[38] A mature medicinal leech may feed only twice a year, taking months to digest a blood meal.[25]
The bodies of predatory leeches are similar, though instead of 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.[39] 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 the soft tissues from their prey, making them intermediate between predators and blood-suckers.[38]
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'
Leeches are unusual in that they do not produce certain
Nervous system
A leech's nervous system is formed of a few large
Leeches have between two and ten pigment spot ocelli, arranged in pairs towards 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 the surroundings.[42]
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 the chances of finding a host.[25]
Gas exchange
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
Movement
Leeches move using their longitudinal and circular muscles in 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 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.[43][25] Leeches explore their environment with head movements and body waving.[44] The Hirudinidae and Erpobdellidae can swim rapidly with up-and-down or sideways undulations of the body; the Glossiphoniidae in contrast are poor swimmers and curl up and fall to the sediment below when disturbed.[45]
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Leeches move by looping using their front and back suckers.[43]
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Video of looping movement
Interactions with humans
Bites
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, a feeling of faintness or dizziness, and difficulty in breathing.[48] 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.[48] Internal attachments, such as inside the nose, are more likely to require medical intervention.[49]
Bacteria, viruses, and protozoan parasites from previous blood sources can survive within 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.[50][51]
Leech saliva is commonly believed to contain
Medical use
The medicinal leech Hirudo medicinalis, and some other
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"Leech finders" fromRobert Havell
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Pharmacy leech jar with airholes in the lid. England, 1830–1870.
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Three leech doctors decide on bloodletting for theirJ. J. Grandville, c. 1832
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.[60]
In the nineteenth century, demand for leeches was sufficient for hirudiculture, the farming of leeches, to become commercially viable.[63] Leech usage declined with the demise of humoral theory,[64] 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.[65][66] Other clinical applications include varicose veins, muscle cramps, thrombophlebitis, and joint diseases such as epicondylitis and osteoarthritis.[67][68][69][70]
Leech secretions contain several bioactive substances with anti-inflammatory, anticoagulant and antimicrobial effects.[69] One active component of leech saliva is a small protein, hirudin.[71] It is widely used as an anticoagulant drug to treat blood-clotting disorders, and manufactured by recombinant DNA technology.[72][73]
In 2012 and 2018, Ida Schnell and colleagues trialled the use of
Water pollution
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.[76]
Notes
- humours, we'll bleed you to-morrow, till then, very little food."
References
- ^ "Proverbs 30:15 | Ellicott's Commentary for English Readers". BibleHub. Retrieved 27 April 2018.
- ^ "Leech". Merriam-Webster. Retrieved 27 April 2018.
- PMID 30474597.
- ^ S2CID 46339662.
- JSTOR 2388511.
- ^ a b Ruppert, Fox & Barnes 2004, p. 471
- ^ Siddall, Mark E. (1998). "Glossiphoniidae". American Museum of Natural History. Archived from the original on 9 August 2019. Retrieved 1 May 2018.
- ^ Ruppert, Fox & Barnes 2004, p. 480
- JSTOR 3222552.
- . Retrieved 23 October 2020.
- ^ "Leeches". Australian Museum. 14 November 2019. Retrieved 3 June 2020.
- ISBN 978-0-8061-3029-3.
- ^ Lamarck, Jean-Baptiste (1818). Histoire naturelle des animaux sans vertèbres ... précédée d'une introduction offrant la détermination des caractères essentiels de l'animal, sa distinction du végétal et des autres corps naturels, enfin, l'exposition des principes fondamentaux de la zoologie. Volume 5. Vol. 5. Paris: Verdière.
- ^ Kolb, Jürgen (2018). "Hirudinea". WoRMS. World Register of Marine Species. Retrieved 7 May 2018.
- ^ PMID 31214691.
- ISBN 978-0-08-092014-6.
- ^ PMID 36310243.
- ^ .
- ISBN 978-0-12-690647-9.
- .
- S2CID 212824469.
- S2CID 219097612.
- ^ Ultrastructure and functional versatility of hirudinean botryoidal tissue
- ^ a b c Ruppert, Fox & Barnes 2004, pp. 471–472
- ^ ISBN 978-1-60535-375-3.
- ^ a b c Ruppert, Fox & Barnes 2004, pp. 474–475
- ^ Spiralian Phylogeny Informs the Evolution of Microscopic Lineages
- ISBN 978-0-226-07874-8.
- ISBN 978-0-87969-146-2.
- ^ S2CID 53218704.
- JSTOR 25129933.
- ^ Reproductive Strategies and Developmental Patterns in Annelids
- ^ Modern Text Book of Zoology: Invertebrates
- ^ a b c d e Ruppert, Fox & Barnes 2004, pp. 477–478
- JSTOR 2424006.
- S2CID 85774943.
- ^ ISBN 978-0-643-09927-2.
- ^ a b c d e Ruppert, Fox & Barnes 2004, pp. 475–477
- ^ Govedich, Fredric R.; Bain, Bonnie A. (14 March 2005). "All about leeches" (PDF). Archived from the original (PDF) on 21 August 2010. Retrieved 19 January 2010.
- ^ Sawyer, Roy T. "Leech biology and behaviour" (PDF). biopharm-leeches.com. Archived from the original (PDF) on 10 September 2011.
- .
- ^ a b Ruppert, Fox & Barnes 2004, pp. 472–474
- ^ )
- ISBN 978-0-87969-146-2.
- ISBN 978-0-471-35837-4.
- ISBN 978-1-74045-739-2.
- ISBN 978-0-9704482-5-5.
- ^ a b Victorian Poisons Information Centre: Leeches Victorian Poisons Information Centre. Retrieved 28 July 2007
- PMID 15815064. See also: lay summaryfrom Reuters, 11 April 2005.
- PMID 21372183.
- S2CID 19770060.
- ^ PMID 2890494.
- ^ Siddall, Mark (7 July 2008). "Myth Busters: Leech Anaesthetic". BdellaNea.
- PMID 22408305.
- PMID 10759861.
- ^ Siddall, Mark; Borda, Liz; Burreson, Gene; et al. "Blood Lust II". Laboratory of Phylohirudinology, American Museum of Natural History. Archived from the original on 7 June 2020. Retrieved 15 December 2013.
- ISBN 978-986-02-2760-4.
- ISBN 978-0-87969-146-2.
- S2CID 18166996.
- ^ ISBN 978-0-7011-8180-2.
- ISBN 978-0-14-044413-1.
- S2CID 18166996.
- William Blackwood and Sons: 641–648.
- ISBN 978-0-241-28715-6.
- ^ Cho, Joohee (4 March 2008). "Some Docs Latching Onto Leeches". ABC News. Retrieved 27 April 2018.
- PMID 3044211.
- S2CID 196365336.
- PMID 12233807.
- ^ PMID 29296560.
- PMID 24019559.
- S2CID 83910684.
- PMID 10560805.
- S2CID 19304703.
- PMID 22537625.
- S2CID 46972335.
- S2CID 220669536.
General bibliography
- Ruppert, Edward E.; Fox, Richard S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th Edition. Cengage Learning. ISBN 978-81-315-0104-7.
External links
- Media related to Hirudinea at Wikimedia Commons
- Data related to Hirudinea at Wikispecies
- The dictionary definition of leech at Wiktionary