Modern Biology Chapter 36 Review Why Are Flatworms Called Acoelomates

Phylum of soft-bodied invertebrates known every bit flatworms

Flatworm Temporal range: 270–0 Ma [ane] PreꞒ Ꞓ O S D C P T J K Pg N Possible Cambrian, Ordovician and Devonian records [2] [iii]
Bedford'south flatworm, Pseudobiceros bedfordi
Scientific classification
Kingdom:	Animalia
Subkingdom:	Eumetazoa
Clade:	ParaHoxozoa
Clade:	Bilateria
Clade:	Nephrozoa
(unranked):	Protostomia
(unranked):	Spiralia
Clade:	Rouphozoa
Phylum:	Platyhelminthes Claus, 1887
Classes
Traditional: Turbellaria Trematoda Monogenea Cestoda Phylogenetic: Catenulida Rhabditophora
Synonyms
Plathelminthes Schneider, 1873 [four]

The flatworms, flat worms, Platyhelminthes, or platyhelminths (from the Greek πλατύ, platy, meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth-, meaning "worm")^[four] are a phylum of relatively simple bilaterian, unsegmented, soft-bodied invertebrates. Different other bilaterians, they are acoelomates (having no trunk cavity), and have no specialized circulatory and respiratory organs, which restricts them to having flattened shapes that let oxygen and nutrients to laissez passer through their bodies by diffusion. The digestive cavity has simply one opening for both ingestion (intake of nutrients) and egestion (removal of undigested wastes); as a result, the food cannot exist processed continuously.

In traditional medicinal texts, Platyhelminthes are divided into Turbellaria, which are mostly not-parasitic animals such as planarians, and three entirely parasitic groups: Cestoda, Trematoda and Monogenea; however, since the turbellarians accept since been proven non to be monophyletic, this classification is now deprecated. Free-living flatworms are more often than not predators, and live in h2o or in shaded, boiling terrestrial environments, such as leafage litter. Cestodes (tapeworms) and trematodes (flukes) have circuitous life-cycles, with mature stages that live as parasites in the digestive systems of fish or land vertebrates, and intermediate stages that infest secondary hosts. The eggs of trematodes are excreted from their main hosts, whereas adult cestodes generate vast numbers of hermaphroditic, segment-like proglottids that detach when mature, are excreted, so release eggs. Dissimilar the other parasitic groups, the monogeneans are external parasites infesting aquatic animals, and their larvae metamorphose into the adult form afterwards attaching to a suitable host.

Because they do not take internal body cavities, Platyhelminthes were regarded equally a primitive stage in the evolution of bilaterians (animals with bilateral symmetry and hence with distinct front and rear ends). However, analyses since the mid-1980s take separated out one subgroup, the Acoelomorpha, as basal bilaterians – closer to the original bilaterians than to whatever other modern groups. The remaining Platyhelminthes form a monophyletic group, ane that contains all and only descendants of a common ancestor that is itself a member of the grouping. The redefined Platyhelminthes is role of the Lophotrochozoa, 1 of the 3 master groups of more complex bilaterians. These analyses had concluded the redefined Platyhelminthes, excluding Acoelomorpha, consists of two monophyletic subgroups, Catenulida and Rhabditophora, with Cestoda, Trematoda and Monogenea forming a monophyletic subgroup within one branch of the Rhabditophora. Hence, the traditional platyhelminth subgroup "Turbellaria" is at present regarded equally paraphyletic, since it excludes the wholly parasitic groups, although these are descended from one group of "turbellarians".

2 planarian species have been used successfully in the Philippines, Indonesia, Hawaii, New Republic of guinea, and Guam to control populations of the imported behemothic African snail Achatina fulica, which was displacing native snails. However, these planarians are themselves a serious threat to native snails and should not exist used for biological command. In northwest Europe, at that place are concerns about the spread of the New Zealand planarian Arthurdendyus triangulatus, which preys on earthworms.

Description [edit]

Distinguishing features [edit]

Platyhelminthes are bilaterally symmetrical animals: their left and correct sides are mirror images of each other; this as well implies they have distinct top and bottom surfaces and distinct head and tail ends. Similar other bilaterians, they have three primary prison cell layers (endoderm, mesoderm, and ectoderm),^[five] while the radially symmetrical cnidarians and ctenophores (comb jellies) have just two cell layers.^[6] Beyond that, they are "defined more by what they practice not have than by any particular series of specializations."^[7] Different other bilaterians, Platyhelminthes accept no internal body cavity, so are described equally acoelomates. They also lack specialized circulatory and respiratory organs, both of these facts are defining features when classifying a flatworm'due south anatomy.^{[5] [8]} Their bodies are soft and unsegmented.^[9]

Attribute	Cnidarians and Ctenophores[6]	Platyhelminthes (flatworms)[five] [eight]	More "advanced" bilaterians[10]
Bilateral symmetry	No	Yeah
Number of main jail cell layers	Two, with jelly-like layer between them	3
Singled-out brain	No	Yes
Specialized digestive system	No	Yes
Specialized excretory organisation	No	Yeah
Body crenel containing internal organs	No		Yes
Specialized circulatory and respiratory organs	No		Yeah

Features common to all subgroups [edit]

The lack of circulatory and respiratory organs limits platyhelminths to sizes and shapes that enable oxygen to reach and carbon dioxide to leave all parts of their bodies by simple diffusion. Hence, many are microscopic and the large species have flat ribbon-like or leafage-like shapes. The guts of large species accept many branches, assuasive nutrients to diffuse to all parts of the body.^[7] Respiration through the whole surface of the body makes them vulnerable to fluid loss, and restricts them to environments where dehydration is unlikely: sea and freshwater, moist terrestrial environments such equally leafage litter or between grains of soil, and as parasites within other animals.^[5]

The infinite between the pare and gut is filled with mesenchyme, also known as parenchyma, a connective tissue made of cells and reinforced by collagen fibers that act as a blazon of skeleton, providing attachment points for muscles. The mesenchyme contains all the internal organs and allows the passage of oxygen, nutrients and waste product products. It consists of ii main types of cell: fixed cells, some of which accept fluid-filled vacuoles; and stem cells, which can transform into any other type of prison cell, and are used in regenerating tissues after injury or asexual reproduction.^[5]

Most platyhelminths accept no anus and regurgitate undigested cloth through the oral fissure. Yet, some long species have an anus and some with circuitous, branched guts take more than than one anus, since excretion only through the oral fissure would exist difficult for them.^[8] The gut is lined with a single layer of endodermal cells that absorb and digest food. Some species break up and soften nutrient commencement by secreting enzymes in the gut or pharynx (throat).^[five]

All animals need to go along the concentration of dissolved substances in their body fluids at a fairly constant level. Internal parasites and free-living marine animals live in environments with loftier concentrations of dissolved textile, and generally let their tissues have the same level of concentration as the environment, while freshwater animals demand to forbid their body fluids from becoming too dilute. Despite this difference in environments, most platyhelminths utilize the aforementioned system to control the concentration of their body fluids. Flame cells, so called considering the beating of their flagella looks like a flickering candle flame, extract from the mesenchyme water that contains wastes and some reusable material, and drive information technology into networks of tube cells which are lined with flagella and microvilli. The tube cells' flagella drive the h2o towards exits called nephridiopores, while their microvilli reabsorb reusable materials and every bit much water as is needed to keep the body fluids at the right concentration. These combinations of flame cells and tube cells are chosen protonephridia.^{[v] [ten]}

In all platyhelminths, the nervous organization is full-bodied at the head end. Other platyhelminths take rings of ganglia in the caput and main nerve trunks running along their bodies.^{[5] [8]}

Major subgroups [edit]

Early on classification divided the flatworms in four groups: Turbellaria, Trematoda, Monogenea and Cestoda. This classification had long been recognized to be artificial, and in 1985, Ehlers^[11] proposed a phylogenetically more right nomenclature, where the massively polyphyletic "Turbellaria" was split into a dozen orders, and Trematoda, Monogenea and Cestoda were joined in the new gild Neodermata. However, the nomenclature presented hither is the early, traditional, classification, as it withal is the ane used everywhere except in scientific articles.^{[5] [12]}

Turbellaria [edit]

These have about 4,500 species,^[8] are by and large complimentary-living, and range from 1 mm (0.04 in) to 600 mm (24 in) in length. Most are predators or scavengers, and terrestrial species are mostly nocturnal and alive in shaded, humid locations, such every bit leafage litter or rotting wood. However, some are symbiotes of other animals, such as crustaceans, and some are parasites. Free-living turbellarians are mostly blackness, brown or greyness, but some larger ones are brightly colored.^[five] The Acoela and Nemertodermatida were traditionally regarded as turbellarians,^{[8] [13]} simply are now regarded as members of a separate phylum, the Acoelomorpha,^[xiv] or every bit 2 separate phyla.^[16] Xenoturbella, a genus of very unproblematic animals,^[17] has also been reclassified as a split up phylum.^[18]

Some turbellarians have a simple pharynx lined with cilia and generally feed by using cilia to sweep nutrient particles and small prey into their mouths, which are usually in the middle of their undersides. Near other turbellarians have a pharynx that is eversible (tin exist extended by existence turned inside-out), and the mouths of dissimilar species can be anywhere along the underside.^[5] The freshwater species Microstomum caudatum can open up its mouth almost every bit wide as its torso is long, to eat casualty about every bit large every bit itself.^[8]

Virtually turbellarians have pigment-cup ocelli ("little optics"); i pair in nigh species, merely ii or even three pairs in others. A few large species have many eyes in clusters over the encephalon, mounted on tentacles, or spaced uniformly around the edge of the body. The ocelli can merely distinguish the direction from which light is coming to enable the animals to avoid information technology. A few groups have statocysts - fluid-filled chambers containing a small, solid particle or, in a few groups, ii. These statocysts are idea to function as balance and acceleration sensors, as they perform the same way in cnidarian medusae and in ctenophores. However, turbellarian statocysts have no sensory cilia, and so the fashion they sense the movements and positions of solid particles is unknown. On the other hand, near have ciliated touch-sensor cells scattered over their bodies, especially on tentacles and effectually the edges. Specialized cells in pits or grooves on the head are most likely smell sensors.^[8]

Planarians, a subgroup of seriates, are famous for their ability to regenerate if divided by cuts beyond their bodies. Experiments show that (in fragments that do not already have a head) a new head grows almost quickly on those fragments which were originally located closest to the original head. This suggests the growth of a caput is controlled by a chemical whose concentration diminishes throughout the organism, from head to tail. Many turbellarians clone themselves by transverse or longitudinal division, whilst others, reproduce by budding.^[8]

The vast majority of turbellarians are hermaphrodites (they accept both female and male reproductive cells) which fertilize eggs internally past copulation.^[8] Some of the larger aquatic species mate by penis fencing – a duel in which each tries to impregnate the other, and the loser adopts the female role of developing the eggs.^[19] In most species, "miniature adults" emerge when the eggs hatch, just a few large species produce plankton-like larvae.^[8]

Trematoda [edit]

These parasites' name refers to the cavities in their holdfasts (Greek τρῆμα, hole),^[5] which resemble suckers and anchor them within their hosts.^[ix] The peel of all species is a syncitium, which is a layer of cells that shares a single external membrane. Trematodes are divided into two groups, Digenea and Aspidogastrea (likewise known equally Aspodibothrea).^[eight]

Digenea [edit]

These are often called flukes, as most have flat rhomboid shapes like that of a flounder (One-time English flóc). At that place are almost 11,000 species, more than all other platyhelminthes combined, and second only to roundworms amongst parasites on metazoans.^[8] Adults usually accept two holdfasts: a ring around the mouth and a larger sucker midway along what would be the underside in a gratuitous-living flatworm.^[5] Although the name "Digeneans" means "two generations", almost have very complex life cycles with up to seven stages, depending on what combinations of environments the early on stages encounter – the most important factor being whether the eggs are deposited on land or in h2o. The intermediate stages transfer the parasites from one host to some other. The definitive host in which adults develop is a country vertebrate; the earliest host of juvenile stages is ordinarily a snail that may live on land or in h2o, whilst in many cases, a fish or arthropod is the 2d host.^[8] For example, the adjoining illustration shows the life cycle of the intestinal fluke metagonimus, which hatches in the intestine of a snail, then moves to a fish where it penetrates the trunk and encysts in the flesh, then migrating to the pocket-size intestine of a land beast that eats the fish raw, finally generating eggs that are excreted and ingested by snails, thereby completing the cycle. A like life wheel occurs with Opisthorchis viverrini, which is institute in South East Asia and tin can infect the liver of humans, causing Cholangiocarcinoma (bile duct cancer). Schistosomes, which cause the devastating tropical disease bilharzia, likewise belong to this group.^[20]

Adults range betwixt 0.ii mm (0.0079 in) and 6 mm (0.24 in) in length. Individual adult digeneans are of a single sexual practice, and in some species slender females alive in enclosed grooves that run along the bodies of the males, partially emerging to lay eggs. In all species the adults accept complex reproductive systems, capable of producing between x,000 and 100,000 times as many eggs equally a free-living flatworm. In add-on, the intermediate stages that alive in snails reproduce asexually.^[eight]

Adults of unlike species infest different parts of the definitive host - for instance the intestine, lungs, big claret vessels,^[5] and liver.^[8] The adults use a relatively large, muscular pharynx to ingest cells, cell fragments, fungus, torso fluids or claret. In both the adult and snail-inhabiting stages, the external syncytium absorbs dissolved nutrients from the host. Developed digeneans can alive without oxygen for long periods.^[eight]

Aspidogastrea [edit]

Members of this small group have either a single divided sucker or a row of suckers that cover the underside.^[8] They infest the guts of bony or cartilaginous fish, turtles, or the body cavities of marine and freshwater bivalves and gastropods.^[5] Their eggs produce ciliated swimming larvae, and the life bicycle has ane or ii hosts.^[viii]

Cercomeromorpha [edit]

These parasites attach themselves to their hosts by means of disks that bear crescent-shaped hooks. They are divided into the Monogenea and Cestoda groupings.^[8]

Monogenea [edit]

Of most ane,100 species of monogeneans, well-nigh are external parasites that require particular host species - mainly fish, but in some cases amphibians or aquatic reptiles. Yet, a few are internal parasites. Developed monogeneans have large attachment organs at the rear, known every bit haptors (Greek ἅπτειν, haptein, ways "catch"), which have suckers, clamps, and hooks. They often take flattened bodies. In some species, the pharynx secretes enzymes to assimilate the host's peel, allowing the parasite to feed on blood and cellular debris. Others graze externally on mucus and flakes of the hosts' skins. The proper name "Monogenea" is based on the fact that these parasites accept only ane nonlarval generation.^[8]

Cestoda [edit]

Life cycle of the eucestode Taenia: Inset 5 shows the scolex, which has iv Taenia solium, a disk with hooks on the end. Inset 6 shows the tapeworm'south whole body, in which the scolex is the tiny, round tip in the tiptop left corner, and a mature proglottid has only detached.

These are often called tapeworms considering of their flat, slender only very long bodies – the name "cestode" is derived from the Latin discussion cestus, which means "tape". The adults of all 3,400 cestode species are internal parasites. Cestodes accept no mouths or guts, and the syncitial pare absorbs nutrients – mainly carbohydrates and amino acids – from the host, and also disguises it chemically to avoid attacks by the host's immune system.^[8] Shortage of carbohydrates in the host's nutrition stunts the growth of parasites and may even kill them. Their metabolisms more often than not employ simple simply inefficient chemical processes, compensating for this inefficiency past consuming large amounts of food relative to their physical size.^[five]

In the bulk of species, known equally eucestodes ("true tapeworms"), the cervix produces a chain of segments called proglottids via a process known every bit strobilation. As a upshot, the most mature proglottids are furthest from the scolex. Adults of Taenia saginata, which infests humans, can course proglottid chains over 20 metres (66 ft) long, although 4 metres (thirteen ft) is more typical. Each proglottid has both male and female reproductive organs. If the host'due south gut contains two or more adults of the same cestode species they generally fertilize each other, however, proglottids of the same worm can fertilize each other and even themselves. When the eggs are fully developed, the proglottids separate and are excreted past the host. The eucestode life wheel is less complex than that of digeneans, just varies depending on the species. For example:

• Adults of Diphyllobothrium infest fish, and the juveniles utilise copepod crustaceans as intermediate hosts. Excreted proglottids release their eggs into the water where the eggs hatch into ciliated, swimming larvae. If a larva is swallowed past a copepod, it sheds the cilia and the pare becomes a syncitium; the larva then makes its way into the copepod's hemocoel (an internal cavity which is the cardinal function of the circulatory arrangement) where it attaches itself using 3 small hooks. If the copepod is eaten by a fish, the larva metamorphoses into a small, unsegmented tapeworm, drills through to the gut and grows into an adult.^[8]
• Various species of Taenia infest the guts of humans, cats and dogs. The juveniles utilise herbivores – such every bit pigs, cattle and rabbits – as intermediate hosts. Excreted proglottids release eggs that stick to grass leaves and hatch after being swallowed past a plant eater. The larva so makes its mode to the herbivore's muscle tissue, where information technology metamorphoses into an oval worm about 10 millimetres (0.39 in) long, with a scolex that is kept internally. When the definitive host eats infested raw or undercooked meat from an intermediate host, the worm's scolex pops out and attaches itself to the gut, when the adult tapeworm develops.^[viii]

Members of the smaller grouping known as Cestodaria take no scolex, do not produce proglottids, and have body shapes similar to those of diageneans. Cestodarians parasitize fish and turtles.^[five]

Nomenclature and evolutionary relationships [edit]

The relationships of Platyhelminthes to other Bilateria are shown in the phylogenetic tree:^[fourteen]

The internal relationships of Platyhelminthes are shown below. The tree is non fully resolved.^{[22] [23] [24]}

The oldest confidently identified parasitic flatworm fossils are cestode eggs found in a Permian shark coprolite, simply helminth hooks however attached to Devonian acanthodians and placoderms might also represent parasitic flatworms with elementary life cycles.^[25] The oldest known gratuitous-living platyhelminth specimen is a fossil preserved in Eocene age Baltic amber and placed in the monotypic species Micropalaeosoma balticus,^[26] whilst the oldest subfossil specimens are schistosome eggs discovered in aboriginal Egyptian mummies.^[9] The Platyhelminthes have very few synapomorphies - distinguishing features that all Platyhelminthes (but no other animals) exhibit. This makes it hard to work out their relationships with other groups of animals, as well as the relationships between different groups that are described as members of the Platyhelminthes.^[27]

The "traditional" view earlier the 1990s was that Platyhelminthes formed the sister group to all the other bilaterians, which include, for instance, arthropods, molluscs, annelids and chordates. Since then, molecular phylogenetics, which aims to work out evolutionary "family unit trees" by comparing different organisms' biochemicals such as Deoxyribonucleic acid, RNA and proteins, has radically changed scientists' view of evolutionary relationships between animals.^[14] Detailed morphological analyses of anatomical features in the mid-1980s, every bit well as molecular phylogenetics analyses since 2000 using unlike sections of DNA, concur that Acoelomorpha, consisting of Acoela (traditionally regarded as very simple "turbellarians"^[8]) and Nemertodermatida (another minor group previously classified every bit "turbellarians"^[thirteen]) are the sister group to all other bilaterians, including the rest of the Platyhelminthes.^[14] However, a 2007 study ended that Acoela and Nemertodermatida were ii distinct groups of bilaterians, although it agreed that both are more closely related to cnidarians (jellyfish, etc.) than other bilaterians are.^[16]

Xenoturbella, a bilaterian whose only well-divers organ is a statocyst, was originally classified equally a "primitive turbellarian".^[17] Later on studies suggested it may instead exist a deuterostome,^{[18] [28]} but more detailed molecular phylogenetics have led to its classification equally sister-group to the Acoelomorpha.^[29]

The Platyhelminthes excluding Acoelomorpha contain two main groups - Catenulida and Rhabditophora - both of which are generally agreed to be monophyletic (each contains all and just the descendants of an antecedent that is a member of the same group).^[22] Early molecular phylogenetics analyses of the Catenulida and Rhabditophora left uncertainties about whether these could be combined in a single monophyletic group; a report in 2008 concluded that they could, therefore Platyhelminthes could be redefined as Catenulida plus Rhabditophora, excluding the Acoelomorpha.

Other molecular phylogenetics analyses agree the redefined Platyhelminthes are most closely related to Gastrotricha, and both are part of a grouping known as Platyzoa. Platyzoa are generally agreed to be at least closely related to the Lophotrochozoa, a superphylum that includes molluscs and annelid worms. The bulk view is that Platyzoa are part of Lophotrochozoa, but a significant minority of researchers regard Platyzoa as a sister group of Lophotrochozoa.^[14]

It has been agreed since 1985 that each of the wholly parasitic platyhelminth groups (Cestoda, Monogenea and Trematoda) is monophyletic, and that together these form a larger monophyletic grouping, the Neodermata, in which the adults of all members take syncytial skins.^[thirty] However, there is argue nigh whether the Cestoda and Monogenea tin exist combined as an intermediate monophyletic group, the Cercomeromorpha, within the Neodermata.^{[30] [31]} It is by and large agreed that the Neodermata are a sub-group a few levels down in the "family tree" of the Rhabditophora. Hence the traditional sub-phylum "Turbellaria" is paraphyletic, since information technology does non include the Neodermata although these are descendants of a sub-grouping of "turbellarians".^[32]

Evolution [edit]

An outline of the origins of the parasitic life manner has been proposed;^[33] epithelial feeding monopisthocotyleans on fish hosts are basal in the Neodermata and were the first shift to parasitism from free living ancestors. The next evolutionary step was a dietary change from epithelium to claret. The last common ancestor of Digenea + Cestoda was monogenean and nigh likely sanguinivorous.

The earliest known fossils confidently classified as tapeworms take been dated to 270 meg years ago, after being found in coprolites (fossilised faeces) from an elasmobranch.^[i] Putative older fossils include a ribbon-shaped, bilaterally symmetrical organism named Rugosusivitta orthogonia from the Early Cambrian of China,^[2] chocolate-brown bodies on the bedding planes reported from the Late Ordovician (Katian) Vauréal Formation (Canada) past Knaust & Desrochers (2019), tentatively interpreted as turbellarians (though the authors cautioned that they might ultimately turn out to be fossils of acoelomorphs or nemerteans)^[iii] and circlets of fossil hooks preserved with placoderm and acanthodian fossils from the Devonian of Latvia, at least some of which might stand for parasitic monogeneans.^[34]

Interaction with humans [edit]

Parasitism [edit]

Cestodes (tapeworms) and digeneans (flukes) cause diseases in humans and their livestock, whilst monogeneans can cause serious losses of stocks in fish farms.^[35] Schistosomiasis, also known equally bilharzia or snail fever, is the second-most devastating parasitic disease in tropical countries, behind malaria. The Carter Center estimated 200 million people in 74 countries are infected with the disease, and one-half the victims live in Africa. The condition has a depression bloodshed rate, merely usually presents as a chronic affliction that tin can damage internal organs. It can impair the growth and cognitive development of children, increasing the risk of bladder cancer in adults. The affliction is caused past several flukes of the genus Schistosoma, which can bore through homo skin; those virtually at risk employ infected bodies of water for recreation or laundry.^[xx]

In 2000, an estimated 45 million people were infected with the beefiness tapeworm Taenia saginata and 3 million with the pork tapeworm Taenia solium.^[35] Infection of the digestive system by developed tapeworms causes abdominal symptoms that, whilst unpleasant, are seldom disabling or life-threatening.^{[36] [37]} However, neurocysticercosis resulting from penetration of T. solium larvae into the fundamental nervous system is the major crusade of caused epilepsy worldwide.^[38] In 2000, about 39 one thousand thousand people were infected with trematodes (flukes) that naturally parasitize fish and crustaceans, simply can pass to humans who eat raw or lightly cooked seafood. Infection of humans past the wide fish tapeworm Diphyllobothrium latum occasionally causes vitamin B₁₂ deficiency and, in severe cases, megaloblastic anemia.^[35]

The threat to humans in developed countries is rising as a upshot of social trends: the increase in organic farming, which uses manure and sewage sludge rather than artificial fertilizers, spreads parasites both straight and via the droppings of seagulls which feed on manure and sludge; the increasing popularity of raw or lightly cooked foods; imports of meat, seafood and salad vegetables from high-chance areas; and, equally an underlying crusade, reduced awareness of parasites compared with other public health issues such as pollution. In less-developed countries, inadequate sanitation and the use of human feces (night soil) as fertilizer or to enrich fish farm ponds continues to spread parasitic platyhelminths, whilst poorly designed water-supply and irrigation projects have provided additional channels for their spread. People in these countries usually cannot afford the cost of fuel required to cook nutrient thoroughly enough to impale parasites. Controlling parasites that infect humans and livestock has become more than difficult, as many species have get resistant to drugs that used to be effective, mainly for killing juveniles in meat.^[35] While poorer countries still struggle with unintentional infection, cases have been reported of intentional infection in the The states by dieters who are drastic for rapid weight-loss.^[39]

Pests [edit]

In that location is concern in northwest Europe (including the British Isles) regarding the possible proliferation of the New Zealand planarian Arthurdendyus triangulatus and the Australian flatworm Australoplana sanguinea, both of which casualty on earthworms.^[40] A. triangulatus is thought to accept reached Europe in containers of plants imported by botanical gardens.^[41]

Benefits [edit]

In Hawaii, the planarian Endeavouria septemlineata has been used to command the imported giant African snail Achatina fulica, which was displacing native snails; Platydemus manokwari, another planarian, has been used for the same purpose in Philippines, Indonesia, New Guinea and Guam. Although A. fulica has declined sharply in Hawaii, there are doubts almost how much Eastward. septemlineata contributed to this decline. However, P. manokwari is given credit for severely reducing, and in places exterminating, A. fulica – achieving much greater success than about biological pest control programs, which by and large aim for a low, stable population of the pest species. The ability of planarians to accept different kinds of prey and to resist starvation may account for their ability to decimate A. fulica. Still, these planarians are a serious threat to native snails and should never be used for biological control.^{[42] [43]}

A report^[44] in La Plata, Argentina, shows the potential for planarians such as Girardia anceps, Mesostoma ehrenbergii, and Bothromesostoma evelinae to reduce populations of the mosquito species Aedes aegypti and Culex pipiens. The experiment showed that Chiliad. anceps in particular can prey on all instars of both musquito species yet maintain a steady predation rate over time. The ability of these flatworms to alive in artificial containers demonstrated the potential of placing these species in pop mosquito breeding sites, which would ideally reduce the corporeality of musquito-borne affliction.

See also [edit]

• Miracidium
• Regenerative medicine
• Schistosoma

References [edit]

1. ^ ^{a b} Dentzien-Dias, PC; Poinar, G Jr; de Figueiredo, AE; Pacheco, AC; Horn, BL; Schultz, CL (30 January 2013). "Tapeworm eggs in a 270 meg-twelvemonth-old shark coprolite". PLOS 1. 8 (1): e55007. Bibcode:2013PLoSO...855007D. doi:10.1371/periodical.pone.0055007. PMC3559381. PMID 23383033.
2. ^ ^{a b} Tang, F.; Song, Southward.; Zhang, Thousand.; Chen, A.; Liu, J. (2021). "Enigmatic ribbon-like fossil from Early Cambrian of Yunnan, China". China Geology. 4 (2): 205–214. doi:10.31035/cg2020056.
3. ^ ^{a b} Dirk Knaust; André Desrochers (2019). "Exceptionally preserved soft-bodied aggregation in Ordovician carbonates of Anticosti Isle, eastern Canada". Gondwana Research. 71: 117–128. Bibcode:2019GondR..71..117K. doi:10.1016/j.gr.2019.01.016.
4. ^ ^{a b}
5. ^ ^{a b c d e f g h i j g fifty m n o p q} Walker, J.C.; Anderson, D.T. (2001). "The Platyhelminthes". In Anderson, D.T. (ed.). Invertebrate Zoology. Oxford University Printing. pp. 58–80. ISBN978-0-19-551368-4.
6. ^ ^{a b} Hinde, R.T. (2001). "The Cnidaria and Ctenophora". In Anderson, D.T. (ed.). Invertebrate Zoology. Oxford University Press. pp. 28–57. ISBN978-0-nineteen-551368-4.
7. ^ ^{a b} Barnes, R.S.1000. (1998). The Diversity of Living Organisms. Blackwell Publishing. pp. 194–195. ISBN978-0-632-04917-2 . Retrieved 2008-12-21 .
8. ^ ^{a b c d e f thou h i j k 50 k due north o p q r s t u v due west x y} Ruppert, E.East.; Fox, R.S. & Barnes, R.D. (2004). Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 226–269. ISBN978-0-03-025982-1.
9. ^ ^{a b c} Klaus Rohde (2001). "Platyhelminthes (Flatworms)". Platyhelminthes (apartment worms). Encyclopedia of Life Sciences. doi:10.1038/npg.els.0001585. ISBN978-0470016176.
10. ^ ^{a b} Ruppert, E.East.; Fox, R.Due south. & Barnes, R.D. (2004). Invertebrate Zoology (7 ed.). Brooks / Cole. pp. 196–224. ISBN978-0-03-025982-1.
11. ^ Ehlers U. (1985). "Phylogenetic relationships within the Plathelminthes", pp 143–158 in The Origins and Relationships of Lower Invertebrates. S Conway Morris, JD George, R Gibson, HM Platt (eds.). Clarendon Press, Oxford.
12. ^ Zoology 2016. Stephen Miller, John Harley. Macmillan/McGraw-Hill School Div. 2015. ISBN978-0-07-667895-2. OCLC 988304549. {{cite volume}}: CS1 maint: others (link)
13. ^ ^{a b} Jondelius, U.; Ruiz-Trillo, I.; Baguñà, J.; Riutort, One thousand. (April 2002). "The Nemertodermatida are basal bilaterians and not members of the Platyhelminthes". Zoologica Scripta. 31 (2): 201–215. doi:10.1046/j.1463-6409.2002.00090.x. S2CID 84015834.
14. ^ ^{a b c d due east} Halanych, 1000. Thou. (2004). "The New View of Animal Phylogeny" (PDF). Almanac Review of Ecology, Evolution, and Systematics. 35: 229–256. doi:10.1146/annurev.ecolsys.35.112202.130124.
15. ^ ^{a b} Wallberg, A.; Curini-Galletti, M.; Ahmadzadeh, A. & Jondelius, U. (September 2007). "Dismissal of Acoelomorpha: Acoela and Nemertodermatida are split up early on bilaterian clades". Zoologica Scripta. 36 (5): 509–523. doi:10.1111/j.1463-6409.2007.00295.x. S2CID 85599100.
16. ^ ^{a b} Westblad, E. (1949). "Xenoturbella bocki north.1000., n.sp., a peculiar, primitive turbellarian blazon". Arkiv för Zoologi. 1: three–29.
17. ^ ^{a b} Bourlat SJ, Nielsen C, Lockyer AE, Littlewood DT, Telford MJ (21 August 2003). "Xenoturbella is a deuterostome that eats molluscs". Nature. 424 (6951): 925–928. Bibcode:2003Natur.424..925B. doi:x.1038/nature01851. PMID 12931184. S2CID 4413357.
18. ^ Newman, Leslie. "Fighting to mate: flatworm penis fencing". PBS. Retrieved 2008-12-21 .
19. ^ ^{a b} The Carter Middle. "Schistosomiasis Command Program". Retrieved 2008-07-17 .
20. ^ Justine JL, Rahmouni C, Gey D, Schoelinck C, Hoberg EP (2013). "The Monogenean which lost its clamps". PLOS I. 8 (11): e79155. Bibcode:2013PLoSO...879155J. doi:10.1371/journal.pone.0079155. PMC3838368. PMID 24278118.
21. ^ ^{a b} Timothy, D.; Littlewood, J.; Telford, Yard. J. & Bray, R. A. (2004). "Protostomes and Platyhelminthes". In Cracraft, J. & Donoghue, M. J. (eds.). Assembling the Tree of Life. Oxford Academy Press The states. pp. 209–223. ISBN978-0-nineteen-517234-8.
22. ^ Boll, P. Thou.; Rossi, I.; Amaral, S. V.; Oliveira, S. Chiliad.; Müller, East. South.; Lemos, V. S.; Leal-Zanchet, A. Thou. (2013). "Platyhelminthes ou apenas semelhantes a Platyhelminthes? Relações filogenéticas dos principais grupos de turbelários". Neotropical Biological science and Conservation. viii (1): 41–52. doi:10.4013/nbc.2013.81.06.
23. ^ Egger, B.; Lapraz, F.; Tomiczek, B.; Müller, Southward.; Dessimoz, C.; Girstmair, J.; Škunca, N.; Rawlinson, K. A.; Cameron, C. B.; Beli, Eastward.; Todaro, M. A.; Gammoudi, M.; Noreña, C.; Telford, One thousand. I. (18 May 2015). "A Transcriptomic-Phylogenomic Analysis of the Evolutionary Relationships of Flatworms". Current Biological science. 25 (x): 1347–1353. doi:ten.1016/j.cub.2015.03.034. PMC4446793. PMID 25866392.
24. ^ De Baets, K., P. Dentzien-Dias, I. Upeniece, O. Verneau and P. C. J. Donoghue (2015-12-xv). "Chapter 3 – Constraining the Deep Origin of Parasitic Flatworms and Host-Interactions with Fossil Evidence". In Kenneth De Baets and D. Timothy J Littlewood (ed.). Advances in Parasitology. Advances in Parasitology. Vol. 90. pp. 93–135. doi:10.1016/bs.apar.2015.06.002. ISBN978-0-12-804001-0. PMID 26597066. {{cite book}}: CS1 maint: multiple names: authors listing (link)
25. ^ Poinar, G. (2003). "A Rhabdocoel Turbellarian (Platyhelminthes, Typhloplanoida) in Baltic Bister with a Review of Fossil and Sub-Fossil Platyhelminths". Invertebrate Biology. 122 (iv): 308–312. doi:ten.1111/j.1744-7410.2003.tb00095.ten. JSTOR 3227067.
26. ^ Carranza, Due south.; Baguñà, J. & Riutort, K. (May 1, 1997). "Are the Platyhelminthes a monophyletic primitive group?". Molecular Biological science and Evolution. 14 (v): 485–497. doi:ten.1093/oxfordjournals.molbev.a025785. PMID 9159926.
27. ^ Bourlat SJ, Juliusdottir T, Lowe CJ, Freeman R, Aronowicz J, Kirschner Thou, Lander ES, Thorndyke G, Nakano H, Kohn AB, Heyland A, Moroz LL, Copley RR, Telford MJ (2006). "Deuterostome phylogeny reveals monophyletic chordates and the new phylum Xenoturbellida". Nature. 444 (7115): 85–88. Bibcode:2006Natur.444...85B. doi:10.1038/nature05241. PMID 17051155. S2CID 4366885.
28. ^ Cannon, J.T.; Vellutini, B.C.; Smith, J.; Ronquist, F.; Jondelius, U.; Hejnol, A. (four February 2016). "Xenacoelomorpha is the sis group to Nephrozoa". Nature. 530 (7588): 89–93. Bibcode:2016Natur.530...89C. doi:ten.1038/nature16520. PMID 26842059. S2CID 205247296.
29. ^ ^{a b} Willems, W.R.; Wallberg, A.; Jondelius, U.; et al. (2005). "Filling a gap in the phylogeny of flatworms: relationships inside the Rhabdocoela (Platyhelminthes), inferred from 18S ribosomal DNA sequences" (PDF). Zoologica Scripta. 35 (1): 1–17. doi:10.1111/j.1463-6409.2005.00216.ten. hdl:1942/1609. S2CID 85917387. Archived from the original (PDF) on 2011-10-06. Retrieved 2008-12-23 .
30. ^ Lockyer, A.Eastward.; Olson, P.D. & Littlewood, D.T.J. (2003). "Utility of complete big and minor subunit rRNA genes in resolving the phylogeny of the Neodermata (Platyhelminthes): implications and a review of the cercomer theory". Biological Journal of the Linnean Society. 78 (2): 155–171. doi:10.1046/j.1095-8312.2003.00141.x.
31. ^ Ehlers, U. (1986). "Comments on a phylogenetic organization of the Platyhelminthes". Hydrobiologia. 132 (1): i–12. doi:x.1007/BF00046222. S2CID 6018712.
32. ^ Perkins, EM; Donnellan, SC; Bertozzi, T; Whittington, ID (2010). "Endmost the mitochondrial circle on paraphyly of the Monogenea (Platyhelminthes) infers evolution in the diet of parasitic flatworms". Int J Parasitol. forty (11): 1237–45. doi:10.1016/j.ijpara.2010.02.017. PMID 20493870.
33. ^ Kenneth De Baets; Paula Dentzien-Dias; Ieva Upeniece; Olivier Verneau; Philip C.J. Donoghue (2015). "Constraining the deep origin of parasitic flatworms and host-interactions with fossil evidence". In Kenneth De Baets; D. Timothy J Littlewood (eds.). Fossil parasites. Advances in Parasitology. Vol. xc. pp. 93–135. doi:10.1016/bs.apar.2015.06.002. ISBN9780128040010. ISSN 0065-308X. PMID 26597066.
34. ^ ^{a b c d} Northrop-Clewes, C.A.; Shaw, C. (2000). "Parasites". British Medical Message. 56 (i): 193–208. doi:10.1258/0007142001902897. PMID 10885116.
35. ^ García, H.H.; Gonzalez, A.Due east.; Evans, C.A.W. & Gilman, R.H. (2003). "Taenia solium cysticercosis". The Lancet. 362 (9383): 547–556. doi:10.1016/S0140-6736(03)14117-7. PMC3103219. PMID 12932389.
36. ^ WHO Expert Committee (1987). "Public health significance of intestinal parasitic infections" (PDF). Bulletin of the World Health Organization. 65 (5): 575–588. PMC2491073. PMID 3501340. Archived from the original (PDF) on 2009-08-16. Retrieved 2008-12-24 .
37. ^ Committee on Tropical Diseases of the International League Against Epilepsy (1994). "Relationship Between Epilepsy and Tropical Diseases". Epilepsia. 35 (i): 89–93. doi:10.1111/j.1528-1157.1994.tb02916.ten. PMID 8112262. S2CID 221733822.
38. ^ "Iowa woman tries 'tapeworm diet', prompts doc warning". Today (U.Southward. TV program). 2013-08-xvi.
39. ^ "Flatworm data sail – Mann Regime" (PDF). Archived from the original (PDF) on 2013-05-01. Retrieved 2014-05-26 .
40. ^ Boag, B.; Yeates, Grand.W. (2001). "The Potential Impact of the New Zealand Flatworm, a Predator of Earthworms, in Western Europe". Ecological Applications. 11 (five): 1276–1286. doi:ten.1890/1051-0761(2001)011[1276:TPIOTN]2.0.CO;ii. ISSN 1051-0761.
41. ^ Barker, G.M. (2004). "Terrestrial planarians". Natural Enemies of Terrestrial Molluscs. CABI Publishing. pp. 261–263. ISBN978-0-85199-319-5.
42. ^ Justine, Jean-Lou; Winsor, Leigh; Gey, Delphine; Gros, Pierre; Thévenot, Jessica (2014). "The invasive New Guinea flatworm Platydemus manokwari in French republic, the first record for Europe: fourth dimension for action is at present". PeerJ. two: e297. doi:10.7717/peerj.297. PMC3961122. PMID 24688873.
43. ^ Tranchida, María C; MacIá, Arnaldo; Brusa, Francisco; Micieli, María V; García, Juan J (2009). "Predation potential of iii flatworm species (Platyhelminthes: Turbellaria) on mosquitoes (Diptera: Culicidae)". Biological Control. 49 (three): 270–276. doi:10.1016/j.biocontrol.2008.12.010.

Further reading [edit]

• Campbell, Neil A. (1996). Biology (Fourth ed.). New York: Benjamin/Cummings Publishing. p. 599. ISBN0-8053-1957-iii.
• Crawley, John 50.; van de Graff, Kent K., eds. (2002). A Photographic Atlas for the Zoology Laboratory (Fourth ed.). Colorado: Morton Publishing Company. ISBN0-89582-613-5.
• The Columbia Electronic Encyclopedia (6th ed.). Columbia University Press. 2004. Retrieved eight February 2005.
• Evers, Christine A.; Starr, Lisa (2006). Biology: Concepts and Applications (6th ed.). United States: Thomson. ISBN0-534-46224-3.
• Saló, E.; Pineda, D.; Marsal, M.; Gonzalez, J.; Gremigni, V.; Batistoni, R. (2002). "Genetic network of the center in Platyhelminthes: Expression and functional assay of some players during planarian regeneration". Factor. 287 (1–ii): 67–74. doi:10.1016/S0378-1119(01)00863-0. PMID 11992724.

External links [edit]

• "Marine flatworms of the earth".
• "Phylum Platyhelminthes".

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Source: https://en.wikipedia.org/wiki/Flatworm

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