40-414: See text Polyopisthocotylea is a subclass of parasitic flatworms in the class Monogenea . There are only two subclasses in the class Monogenea : The subclass Polyopisthocotylea contains the four following orders: Monogenea See text . Monogeneans , members of the class Monogenea , are a group of ectoparasitic flatworms commonly found on the skin, gills , or fins of fish. They have
80-768: A slimming aid has been touted since around 1900. All 6,000 species of Cestoda are parasites , mainly intestinal; their definitive hosts are vertebrates, both terrestrial and marine, while their intermediate hosts include insects, crustaceans, molluscs, and annelids as well as other vertebrates. T. saginata , the beef tapeworm, can grow up to 20 m (65 ft); the largest species, the whale tapeworm Tetragonoporus calyptocephalus , can grow to over 30 m (100 ft). Species with small hosts tend to be small. For example, vole and lemming tapeworms are only 13–240 mm (0.5–9.4 in) in length, and those parasitizing shrews only 0.8–60 mm (0.03–2.36 in). Cestodes have no gut or mouth and absorb nutrients from
120-412: A direct lifecycle and do not require an intermediate host. Adults are hermaphrodites, meaning they have both male and female reproductive structures. Some monogeneans are oviparous (egg-laying) and some are viviparous (live-bearing). Oviparous varieties release eggs into the water. Viviparous varieties release larvae, which immediately attach to another host. The genus Gyrodactylus is an example of
160-427: A few are viviparous. The following cladogram depicts the phylogenetic relationships of the different monogenean orders: Monocotylidea Capsalidea Lagarocotylidea Montchadskyellidea Gyrodactylidea Dactylogyridea Polystomatidea Chimaericolidea Diclybothriidea Mazocraeidea The ancestors of Monogenea were probably free-living flatworms similar to modern Turbellaria . According to
200-581: A head region that contains concentrated sense organs and nervous tissue (brain). Like all ectoparasites, monogeneans have well-developed attachment structures. The anterior structures are collectively termed the prohaptor , while the posterior ones are collectively termed the opisthaptor , or simply haptor . The posterior opisthaptor with its hooks, anchors, clamps etc. is typically the major attachment organ. Generally, monogeneans also are hermaphroditic with functional reproductive organs of both sexes occurring in one individual. Most species are oviparous, but
240-409: A minnow or other small freshwater fish, the procercoid larvae migrate into the fish's flesh where they develop into plerocercoid larvae. These are the infective stages for the mammalian definitive host. If the small fish is eaten by a predatory fish, its muscles too can become infected. Schistocephalus solidus is another three-phase example. The intermediate hosts are copepods and small fish, and
280-942: A pinkish fluid. Gills that are infected may appear swollen and pale. "Pipping", which is gulping for air at the water surface, could indicate severe respiratory distress. In salt water fish, Monogeneans can infect the skin and gills, resulting in irritations to the host. Heavy infections could result in erratic swimming behavior. Affected gills may become irritated and swollen. Monogenea are small parasitic flatworms mainly found on skin or gills of fish. They are rarely longer than about 2 cm. A few species infecting certain marine fish are larger, and marine forms are generally larger than those found on freshwater hosts. Monogenea are often capable of dramatically elongating and shortening as they move. Biologists need to ensure that specimens are completely relaxed before measurements are taken. Monogeneans lack respiratory, skeletal, and circulatory systems but they do have posterior attachment structures in
320-442: A scolex (head), a short neck, and a strobila (segmented body) formed of proglottids . Tapeworms anchor themselves to the inside of the intestine of their host using their scolex, which typically has hooks, suckers , or both. They have no mouth, but absorb nutrients directly from the host's gut. The neck continually produces proglottids, each one containing a reproductive tract; mature proglottids are full of eggs, and fall off to leave
360-401: A single lobed or unlobed ovary with the connecting oviduct and uterus as female organs. The common external opening for both male and female reproductive systems is known as the genital pore, which is situated at the surface opening of the cup-shaped atrium. Though they are sexually hermaphroditic and cross-fertilization is the norm, self-fertilization sometimes occurs and makes possible
400-582: A strobila, or segmented trunk formed of proglottids, which makes up the worm's body. Members of the subclass Cestodaria , the Amphilinidea and Gyrocotylidea , are wormlike but not divided into proglottids. Amphilinids have a muscular proboscis at the front end; Gyrocotylids have a sucker or proboscis which they can pull inside or push outside at the front end, and a holdfast rosette at the posterior end. The Cestodaria have 10 larval hooks while Eucestoda have 6 larval hooks. The scolex, which attaches to
440-403: A two-phase life cycle with two types of host. The adult Taenia saginata lives in the gut of a primate such as a human, its definitive host. Proglottids leave the body through the anus and fall to the ground, where they may be eaten with grass by a grazing animal such as a cow. This animal then becomes an intermediate host, the oncosphere boring through the gut wall and migrating to another part of
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#1732793041120480-414: A viviparous variety, while the genus Dactylogyrus is an example of an oviparous variety. Freshwater fish that become infected with this parasite become lethargic and end up swimming towards the surface of the water. In addition, some may be seen rubbing the bottom or sides of their skin where the parasite is located. Infected skin where the parasite is attached may show areas of scale loss and may produce
520-416: Is composed of a series of segments called proglottids . These are produced from the neck by mitotic growth, which is followed by transverse constriction. The segments become larger and more mature as they are displaced backwards by newer segments. Each proglottid contains an independent reproductive tract, and like some other flatworms, cestodes excrete waste through flame cells ( protonephridia ) located in
560-574: Is shown in the phylogenetic tree . The non-parasitic flatworms, traditionally grouped as the " Turbellaria ", are paraphyletic , as the parasitic Neodermata including the Cestoda arose within that grouping. The approximate times when major groups first appeared is shown in millions of years ago. Gastrotricha [REDACTED] " Turbellaria " [REDACTED] [REDACTED] [REDACTED] [REDACTED] Mollusca [REDACTED] Annelida [REDACTED] The evolutionary history of
600-513: The digestive tracts of vertebrates , while the larvae often live in the bodies of other animals, either vertebrates or invertebrates. For example, Diphyllobothrium has at least two intermediate hosts, a crustacean and then one or more freshwater fish; its definitive host is a mammal. Some cestodes are host-specific, while others are parasites of a wide variety of hosts . Some six thousand species have been described; probably all vertebrates can host at least one species. The adult tapeworm has
640-433: The hippopotamus . Gastrocotylinae – Family of worms Cestodes Cestoda is a class of parasitic worms in the flatworm phylum (Platyhelminthes). Most of the species—and the best-known—are those in the subclass Eucestoda ; they are ribbon-like worms as adults, known as tapeworms . Their bodies consist of many similar units known as proglottids—essentially packages of eggs which are regularly shed into
680-416: The Cestoda has been studied using ribosomal RNA , mitochondrial and other DNA, and morphological analysis and continues to be revised. " Tetraphyllidea " is seen to be paraphyletic; " Pseudophyllidea " has been broken up into two orders, Bothriocephalidea and Diphyllobothriidea . Hosts, whose phylogeny often mirrors that of the parasites ( Fahrenholz's rule ), are indicated in italics and parentheses,
720-549: The Ediacaran-Cambrian border, has great similarities to present day Cestodians. If correct, this would be the earliest example of a Platyzoan and also one of the earliest bilaterian body-fossils and might thus provide an insight to the living mode of Cestodians before they became specialized parasites. The position of the Cestoda within the Platyhelminthes and other Spiralian phyla based on genomic analysis
760-660: The Monogenea into two (or three) subclasses based on the complexity of their haptor: the Monopisthocotylea have one main part to the haptor, often with hooks or a large attachment disc, whereas the Polyopisthocotylea have multiple parts to the haptor, typically clamps. These groups are also known as Polyonchoinea and Heteronchoinea, respectively. Polyopisthocotyleans are almost exclusively gill-dwelling blood feeders, whereas monopisthocotyleans may live on
800-434: The body such as the muscle. Here it encysts, forming a cysticercus . The parasite completes its life cycle when the intermediate host passes on the parasite to the definitive host, usually when the definitive host eats contaminated parts of the intermediate host, for example a human eating raw or undercooked meat. Another two-phase life cycle is exhibited by Anoplocephala perfoliata , the definitive host being an equine and
840-656: The definitive hosts are waterbirds. This species has been used to demonstrate that cross-fertilisation produces a higher infective success rate than self-fertilisation. Hosts can become immune to infection by a cestode if the lining, the mucosa, of the gut is damaged. This exposes the host's immune system to cestode antigens , enabling the host to mount an antibody defence. Host antibodies can kill or limit cestode infection by damaging their digestive enzymes, which reduces their ability to feed and therefore to grow and to reproduce; by binding to their bodies; and by neutralising toxins that they produce. When cestodes feed passively in
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#1732793041120880-409: The environment to infect other organisms. Species of the other subclass, Cestodaria , are mainly fish infecting parasites. All cestodes are parasitic ; many have complex life histories , including a stage in a definitive (main) host in which the adults grow and reproduce, often for years, and one or two intermediate stages in which the larvae develop in other hosts. Typically the adults live in
920-439: The form of adhesives, clamps, hamuli and suckers. Like other flatworms, Monogenea have no true body cavity (coelom). They have a simple digestive system consisting of a mouth opening with a muscular pharynx and an intestine with no terminal opening ( anus ). Monogenea are Platyhelminthes, so are among the lowest invertebrates to possess three embryonic germ layers— endoderm , mesoderm , and ectoderm . In addition, they have
960-439: The gills, skin, and fins. Monopisthocotylea include: All of these can cause epizootics in freshwater fish when raised in aquaculture . Polyopisthocotylea include: Monogeneans possess the simplest lifecycle among the parasitic platyhelminths. They have no intermediate hosts and are ectoparasitic on fish (seldom in the urinary bladder and rectum of cold-blooded vertebrates ). Although they are hermaphrodites ,
1000-420: The gut or body wall to reach the coelom ) are intestinal, though some life cycle stages rest in muscle or other tissues. The definitive host is always a vertebrate but in nearly all cases, one or more intermediate hosts are involved in the life cycle, typically arthropods or other vertebrates. Infections can be long-lasting; in humans, tapeworm infection may last as much as 30 years. No asexual phases occur in
1040-651: The gut, they do not provoke an antibody reaction. Parasite fossils are rare, but recognizable clusters of cestode eggs, some with an operculum (lid) indicating that they had not erupted, one with a developing larva, have been discovered in fossil shark coprolites dating to the Permian , some 270 million years ago. The fossil Rugosusivitta , which was found in China at base of the Cambrian deposits in Yunnan just above
1080-558: The host in feces, or migrate outwards as independent motile proglottids. The number of proglottids forming the tapeworm ranges from three to four thousand. Their layout comes in two forms: craspedote, meaning any given proglottid is overlapped by the previous proglottid, or acraspedote, indicating the proglottids do not overlap. Cestodes are exclusively hermaphrodites , with both male and female reproductive systems in each body. The reproductive system includes one or more testes, cirri, vas deferens , and seminal vesicles as male organs, and
1120-411: The host's alimentary tract through their specialised neodermal cuticle, or tegument , through which gas exchange also takes place. The tegument also protects the parasite from the host's digestive enzymes and allows it to transfer molecules back to the host. The body form of adult eucestodes is simple, with a scolex, or grasping head, adapted for attachment to the definitive host , a short neck, and
1160-513: The host, either passively in the feces or actively moving. All tapeworms are hermaphrodites, with each individual having both male and female reproductive organs. Humans are subject to infection by several species of tapeworms if they eat undercooked meat such as pork ( Taenia solium ), beef ( T. saginata ), and fish ( Diphyllobothrium ), or if they live in, or eat food prepared in, conditions of poor hygiene ( Hymenolepis or Echinococcus species). The unproven concept of using tapeworms as
1200-413: The intermediate host an oribatid mite . Diphyllobothrium exhibits a more complex, three-phase life cycle. If the eggs are laid in water, they develop into free-swimming oncosphere larvae. After ingestion by a suitable freshwater crustacean such as a copepod , the first intermediate host, they develop into procercoid larvae. When the copepod is eaten by a suitable second intermediate host, typically
1240-477: The intestine of the definitive host, is often minute in comparison with the proglottids. It is typically a four-sided knob, armed with suckers or hooks or both. In some species, the scolex is dominated by bothria , or "sucking grooves" that function like suction cups . Cyclophyllid cestodes can be identified by the presence of four suckers on their scolices. Other species have ruffled or leaflike scolices, and there may be other structures to aid attachment. In
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1280-404: The larval stage the scolex is similarly shaped and is known as the protoscoleces. Circular and longitudinal muscles lie under the neodermis, beneath which further longitudinal, dorso-ventral and transverse muscles surround the central parenchyma . Protonephridial cells drain into the parenchyma. There are four longitudinal collection canals, two dorso-lateral and two ventro-lateral, running along
1320-521: The length of the strobila. The cirrus and vagina are innervated, and sensory endings around the genital pore are more plentiful than in other areas. Sensory function includes both tactoreception (touch) and chemoreception (smell or taste). Once anchored to the host's intestinal wall, tapeworms absorb nutrients through their surface as their food flows past them. Cestodes are unable to synthesise lipids, which they use for reproduction, and are therefore entirely dependent on their hosts. The tapeworm body
1360-413: The length of the worm, with a transverse canal linking the ventral ones at the posterior of each segment. When the proglottids begin to detach, these canals open to the exterior through the terminal segment. The main nerve centre of a cestode is a cerebral ganglion in its scolex. Nerves emanate from the ganglion to supply the general body muscular and sensory endings, with two lateral nerve cords running
1400-555: The life cycle, as they do in other flatworms , but the life cycle pattern has been a crucial criterion for assessing evolution among Platyhelminthes. Cestodes produce large numbers of eggs, but each one has a low probability of finding a host. To increase their chances, different species have adopted various strategies of egg release. In the Pseudophyllidea, many eggs are released in the brief period when their aquatic intermediate hosts are abundant (semelparity). In contrast, in
1440-406: The male reproductive system becomes functional before the female part. The eggs hatch releasing a heavily ciliated larval stage known as an oncomiracidium . The oncomiracidium has numerous posterior hooks and is generally the life stage responsible for transmission from host to host. No known monogeneans infect birds , but one ( Oculotrema hippopotami ) infects mammals , parasitizing the eye of
1480-430: The more widely accepted view, "rhabdocoel turbellarians gave rise to monogeneans; these, in turn, gave rise to digeneans , from which the cestodes were derived. Another view is that the rhabdocoel ancestor gave rise to two lines; one gave rise to monogeneans, which gave rise to digeneans, and the other line gave rise to cestodes". About 50 families and thousands of species are described . Some parasitologists divide
1520-421: The proglottids. The sum of the proglottids is called a strobila, which is thin and resembles a strip of tape; from this is derived the common name "tapeworm". Proglottids are continually being produced by the neck region of the scolex, as long as the scolex is attached and alive. Mature proglottids are essentially bags of eggs, each of which is infective to the proper intermediate host. They are released and leave
1560-420: The reproduction of a worm when it is the only individual in its host's gut. During copulation, the cirri of one individual connect with those of the other through the genital pore, and then spermatozoa are exchanged. Cestodes are parasites of vertebrates, with each species infecting a single definitive host or group of closely related host species. All but amphilinids and gyrocotylids (which burrow through
1600-478: The terrestrial Cyclophyllidea, proglottids are released steadily over a period of years, or as long as their host lives (iteroparity). Another strategy is to have very long-lived larvae; for example, in Echinococcus , the hydatid larvae can survive for ten years or more in humans and other vertebrate hosts, giving the tapeworm an exceptionally long time window in which to find another host. Many tapeworms have
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