In biological classification , class ( Latin : classis ) is a taxonomic rank , as well as a taxonomic unit, a taxon , in that rank. It is a group of related taxonomic orders. Other well-known ranks in descending order of size are life , domain , kingdom , phylum , order , family , genus , and species , with class ranking between phylum and order.
50-403: 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 the environment to infect other organisms. Species of
100-405: A host or substrate. In parasitic annelids , flatworms and roundworms , suckers are the organs of attachment to the host tissues. In tapeworms and flukes , they are a parasitic adaptation for attachment on the internal tissues of the host, such as intestines and blood vessels. In roundworms and flatworms they serve as attachment between individuals particularly during mating . In annelids,
150-763: 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
200-407: A central hollow cavity called acetabulum . Both these structures are thick muscles, and are covered with chitinous cuticle to make a protective surface. It is used for grasping substratum, catching prey and for locomotory accessory. When the sucker attaches itself on an object, the infundibulum mainly provides adhesion while the central acetabulum is quite free. The sequential muscle contraction
250-551: A distinct grade of organization—i.e. a 'level of complexity', measured in terms of how differentiated their organ systems are into distinct regions or sub-organs—with a distinct type of construction, which is to say a particular layout of organ systems. This said, the composition of each class is ultimately determined by the subjective judgment of taxonomists . In the first edition of his Systema Naturae (1735), Carl Linnaeus divided all three of his kingdoms of nature ( minerals , plants , and animals ) into classes. Only in
300-424: A distinct rank of biological classification having its own distinctive name – and not just called a top-level genus (genus summum) – was first introduced by French botanist Joseph Pitton de Tournefort in the classification of plants that appeared in his Eléments de botanique of 1694. Insofar as a general definition of a class is available, it has historically been conceived as embracing taxa that combine
350-408: 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
400-442: 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
450-399: 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
500-579: 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
550-399: A sucker can be both a functional mouth and a locomotory organ . The structure and number of suckers are often used as basic taxonomic diagnosis between different species, since they are unique in each species. In tapeworms there are two distinct classes of suckers, namely "bothridia" for true suckers, and " bothria " for false suckers. In digeneal flukes there are usually an oral sucker at
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#1732801442128600-419: A taxonomy of the flowering plants up to the level of orders, many sources have preferred to treat ranks higher than orders as informal clades . Where formal ranks have been assigned, the ranks have been reduced to a very much lower level, e.g. class Equisitopsida for the land plants, with the major divisions within the class assigned to subclasses and superorders. The class was considered the highest level of
650-403: 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
700-476: Is a protruding cuticle and circular in shape. Annelid worms such as leeches all have an anterior (oral) sucker formed from the first six segments of their body, which is used to connect to a host for feeding. It also releases an anaesthetic to prevent the host from feeling pain while it sucks blood. They use a combination of mucus and suction (caused by concentric muscles in those six segments) to stay attached and secrete an anti-clotting enzyme, hirudin, into
750-415: 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
800-572: 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
850-515: The Western sucker-footed bat have unusual suckers on their limbs that are useful during roosting . Some amphibians such as the frog have adhesive pads on their toes to help with their locomotion . In the class Turbellaria , only the species of the order Temnocephalida are parasitic and possess an adhesive disc. The sucker is present at the posterior end on the ventral side. It is lined with syncytial epidermis and numerous microvilli. Beneath
900-413: 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,
950-549: 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
1000-473: The acetabulum. Cephalopods are characterised by elongated appendages known as cephalopod limbs for locomotion and grasping objects. There are two main types: arms , such as in octopus , bearing numerous suckers along its ventral surface; and tentacles , such as in squid and cuttlefish , having a single sucker at the tip. Each sucker is a circular and bowl-like curved disc. It in turn has two distinct parts: an outer shallow cavity called infundibulum and
1050-460: The animal kingdom are Linnaeus's classes similar to the classes used today; his classes and orders of plants were never intended to represent natural groups, but rather to provide a convenient "artificial key" according to his Systema Sexuale , largely based on the arrangement of flowers. In botany, classes are now rarely discussed. Since the first publication of the APG system in 1998, which proposed
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#17328014421281100-435: The apical membrane are many vacuoles and dense bodies. It is attached to the body through a short stalk. Densely packed muscle fibres link the sucker with the main body through the stalk. Udonellids are symbiotic to fishes, on which body they remain attached using a sucker. The sucker is a membranous extension of the posterior end. It has an indistinct stalk and the anterior surface is lined with microvilli. Some portion of
1150-433: 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
1200-655: 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
1250-404: The flukes belonging to class Digenea , there are two suckers, namely an oral sucker and a ventral sucker (often called acetabulum ). The oral sucker is at the tip of the anterior body and directly surrounds the mouth. The ventral sucker is located halfway to the middle of the body on the ventral side. They are both used for attachment to intestinal wall and blood vessels. The detailed structure of
1300-417: 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
1350-647: 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
1400-556: 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
1450-407: 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
1500-414: The host's blood stream. The medicinal leech ( Hirudo medicinalis ) has two suckers, one at each end, called the anterior and posterior sucker. The posterior is mainly used for leverage while the anterior sucker, consisting of the jaw and teeth , is where the feeding takes place. During locomotion directional movement of the body is done by successive attachment and detachment of the oral sucker and
1550-513: 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
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1600-423: The infundibulum and acetabulum causes attachment and detachment. Gobies , remoras and lumpsuckers have suckers which are modified fins. These fishes use their suckers to cling to substrata or to bigger fishes. In gobies the disc-shaped sucker is formed from fused pelvic fins. Amphidromous gobies particularly use their suckers for climbing through waterfalls during their developmental migrations. In remoras
1650-412: 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
1700-474: 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
1750-466: 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
1800-403: 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
1850-517: 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
1900-412: 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
1950-554: 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
2000-1097: The life-cycle sequence (where known) shown by arrows as (intermediate host 1 [→ intermediate host 2 ] → definitive host) . Alternatives, generally for different species within an order, are shown in square brackets. Gyrocotylidea (fishes) Amphilinidea (crustaceans → fishes/turtles) Spathebothriidea (amphipods → fishes) Caryophyllidea (annelids → fishes) Haplobothriidea (freshwater fishes → bowfin ) Diphyllobothriidea (copepods [→ fishes] → mammals) Diphyllidea (elasmobranchs inc. rays, sharks) Trypanorhyncha (fishes/crustaceans/molluscs → bony fishes/selachians) Bothriocephalidea (crustaceans [→ teleost] → teleost fishes/amphibians) Litobothriidea (lamniform sharks) Lecanicephalidea (molluscs → selachians) Rhinebothriidea (stingrays) " Tetraphyllidea " (copepods → fishes/decapods/cephalopods → selachians) " Tetraphyllidea " Proteocephalidea (crustaceans → inverts/verts → fishes/amphibians/reptiles) Nippotaeniidea (crustaceans → fishes) Class (biology) The class as
2050-433: The main body through a small stalk. The surface is profusely covered with microvilli. It is used for symbiotic association with fishes. Parasitic roundworms such as species of Ascaridia and Heterakis possess a single sucker at the posterior end of the body, just in front of anus, hence is often called a pre-anal sucker. Only the male roundworms have them, and are used for attachment to female during mating. The sucker
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2100-464: The mouth and a ventral sucker (or acetabulum ) posterior to the mouth. Roundworms have their sucker just in front of the anus; hence it is often called a pre-anal sucker. Among chordates , some fishes and mammals have suckers, which are used as a holdfast to substrata. Among fishes some members of the order Perciformes have modified fins that form a sucker. Some bats , the Madagascar and
2150-402: 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 the digestive tracts of vertebrates , while
2200-420: 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
2250-418: 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
2300-523: The sucker is a modified dorsal fin. In lumpsuckers, also known as lumpfish, the sucker is formed from modified pelvic fins, located ventrally, and behind the pectoral fins . A fish family the Catostomidae are known as suckers . These fish have a suckermouth . Certain species of bats such as Madagascar sucker-footed bat and Western sucker-footed bat , are generally called "sucker-footed bats" because of suckers on their limbs. They are members of
2350-423: The suckers, presence or absence of hooks, and their exact position on the body are major taxonomic keys between species. In the class Monogenea , oral suckers are present in worm parasites of the order Mazocraeidea . They are known to have muscular, glandular, and sensory components thought to play some role in blood feeding. In other species like Anoplodiscus , the sucker is a posterior extension, connected to
2400-434: The taxonomic hierarchy until George Cuvier 's embranchements , first called Phyla by Ernst Haeckel , were introduced in the early nineteenth century. Sucker (zoology) A sucker in zoology is a specialised attachment organ of an animal. It acts as an adhesion device in parasitic worms , several flatworms , cephalopods , certain fishes , amphibians , and bats . It is a muscular structure for suction on
2450-427: The tegument has interconnected surface extension appearing as loops. The interior is divided into several compartments which are surrounded by interconnected connective tissue . The connective tissues are linked with muscles that extend into the main body. In tapeworms, the sucker is called bothridium (plural "bothridia") to differentiate it from the sucker-like protrusion called bothrium in some species. Among
2500-477: 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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