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84-842: Provorticidae is a family of flatworms belonging to the order Rhabdocoela . Genera: Flatworms Traditional: Phylogenetic: The flatworms , flat worms , Platyhelminthes , or platyhelminths (from the Greek πλατύ, platy , meaning "flat" and ἕλμινς (root: ἑλμινθ-), helminth- , meaning " worm ") are a phylum of relatively simple bilaterian , unsegmented , soft-bodied invertebrates . Being acoelomates (having no body cavity ), and having no specialised circulatory and respiratory organs , they are restricted to having flattened shapes that allow oxygen and nutrients to pass through their bodies by diffusion . The digestive cavity has only one opening for both ingestion (intake of nutrients) and egestion (removal of undigested wastes); as

168-515: A monophyletic group, one that contains all and only descendants of a common ancestor that is itself a member of the group. The redefined Platyhelminthes is part of the Lophotrochozoa , one of the three main 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

252-977: A phylogenetically more correct classification, where the massively polyphyletic "Turbellaria" was split into a dozen orders, and Trematoda, Monogenea and Cestoda were joined in the new order Neodermata . However, the classification presented here is the early, traditional, classification, as it still is the one used everywhere except in scientific articles. These have about 4,500 species, are mostly free-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 live in shaded, humid locations, such as leaf litter or rotting wood. However, some are symbiotes of other animals, such as crustaceans , and some are parasites . Free-living turbellarians are mostly black, brown or gray, but some larger ones are brightly colored. The Acoela and Nemertodermatida were traditionally regarded as turbellarians, but are now regarded as members of

336-415: A planetary body after the former is introduced by a space probe or spacecraft , either deliberately or unintentionally. It has also been hypothesized that the origin of life on earth is due to introductions of life from other planets billions of years ago, possibly by a sentient race. Projects have been proposed to introduce life to other lifeless but habitable planets in other star systems some time in

420-409: A few are internal parasites. Adult monogeneans have large attachment organs at the rear, known as haptors (Greek ἅπτειν, haptein , means "catch"), which have suckers , clamps , and hooks. They often have flattened bodies. In some species, the pharynx secretes enzymes to digest the host's skin, allowing the parasite to feed on blood and cellular debris. Others graze externally on mucus and flakes of

504-507: A fish where it penetrates the body and encysts in the flesh, then migrating to the small intestine of a land animal that eats the fish raw, finally generating eggs that are excreted and ingested by snails, thereby completing the cycle. A similar life cycle occurs with Opisthorchis viverrini , which is found in South East Asia and can infect the liver of humans, causing Cholangiocarcinoma (bile duct cancer). Schistosomes, which cause

588-417: A free-living flatworm. In addition, the intermediate stages that live in snails reproduce asexually. Adults of different species infest different parts of the definitive host - for example the intestine , lungs , large blood vessels, and liver. The adults use a relatively large, muscular pharynx to ingest cells, cell fragments, mucus , body fluids or blood. In both the adult and snail-inhabiting stages,

672-541: A monophyletic subgroup within one branch of the Rhabditophora. Hence, the traditional platyhelminth subgroup "Turbellaria" is now regarded as paraphyletic , since it excludes the wholly parasitic groups, although these are descended from one group of "turbellarians". Two planarian species have been used successfully in the Philippines , Indonesia , Hawaii , New Guinea , and Guam to control populations of

756-830: A native of East Asia, has been introduced into parts of Europe for ornamental reasons. Many plants have been introduced with the intent of aesthetically improving public recreation areas or private properties. The introduced Norway maple for example occupies a prominent status in many of Canada's parks. The transport of ornamental plants for landscaping use has and continues to be a source of many introductions. Some of these species have escaped horticultural control and become invasive. Notable examples include water hyacinth , salt cedar , and purple loosestrife . In other cases, species have been translocated for reasons of "cultural nostalgia", which refers to instances in which humans who have migrated to new regions have intentionally brought with them familiar organisms. Famous examples include

840-437: A new region may escape from captive or cultivated populations and subsequently establish independent breeding populations. Escaped organisms are included in this category because their initial transport to a new region is human motivated. The widespread phenomena of intentional introduction has also been described as biological globalization . Positive Introductions Although most introduced species have negative impacts on

924-584: A novel environment (e.g.: in Europe , house sparrows are well established since early Iron Age though they originated from Asia ). Immigrant species are species that travel, sometimes by themselves, but often with human help, between two habitats. Invasiveness is not a requirement. Introduction of a species outside its native range is all that is required to be qualified as an "introduced species". Such species might be termed naturalized , "established", or "wild non-native species". If they further spread beyond

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1008-463: A parasite or herbivore with it. Some become invasive, for example, the oleander aphid , accidentally introduced with the ornamental plant, oleander . Yet another unintentional pathway of introduction is during the delivery of humanitarian aid in the aftermath of natural disasters. This occurred during relief efforts for Hurricane Maria in Dominica , it was found that the common green iguana ,

1092-605: A pharynx that is eversible (can be extended by being turned inside-out), and the mouths of different species can be anywhere along the underside. The freshwater species Microstomum caudatum can open its mouth almost as wide as its body is long, to swallow prey about as large as itself. Predatory species in suborder Kalyptorhynchia often have a muscular pharynx equipped with hooks or teeth used for seizing prey. Most turbellarians have pigment-cup ocelli ("little eyes"); one pair in most species, but two or even three pairs in others. A few large species have many eyes in clusters over

1176-467: A population decrease. This was seen in the Atlantic Salmon population when high levels of escape from Atlantic Salmon farms into the wild populations resulted in hybrids that had reduced survival. Potential positive effects include adding to the genetic diversity of the population which can increase the adaptation ability of the population and increase the number of healthy individuals within

1260-758: A population. This was seen in the introduction of guppies in Trinidad to encourage population growth and introduce new alleles into the population. The results of this introduction included increased levels of heterozygosity and a larger population size . Wide-spread introductions of non-native iguanas are causing devastating effects on native Iguana populations in the Caribbean Lesser Antilles , as hybrids appear to have higher fitness than native iguanas, leading to competitive outcompetition and replacement. Numerous populations have already become extinct and hybridization continues to reduce

1344-649: A result, the food can not be processed continuously. In traditional medicinal texts, Platyhelminthes are divided into Turbellaria , which are mostly non- parasitic animals such as planarians , and three entirely parasitic groups: Cestoda , Trematoda and Monogenea ; however, since the turbellarians have since been proven not to be monophyletic , this classification is now deprecated. Free-living flatworms are mostly predators, and live in water or in shaded, humid terrestrial environments, such as leaf litter . Cestodes (tapeworms) and trematodes (flukes) have complex life-cycles, with mature stages that live as parasites in

1428-420: A ring around the mouth and a larger sucker midway along what would be the underside in a free-living flatworm. Although the name "Digeneans" means "two generations", most have very complex life cycles with up to seven stages, depending on what combinations of environments the early stages encounter – the most important factor being whether the eggs are deposited on land or in water. The intermediate stages transfer

1512-469: A separate phylum, the Acoelomorpha , or as two separate phyla. Xenoturbella , a genus of very simple animals, has also been reclassified as a separate phylum. Some turbellarians have a simple pharynx lined with cilia and generally feed by using cilia to sweep food particles and small prey into their mouths, which are usually in the middle of their undersides. Most other turbellarians have

1596-449: A species is considered "introduced" when its transport into an area outside of its native range is human mediated. Introductions by humans can be described as either intentional or accidental. Intentional introductions have been motivated by individuals or groups who either (1) believe that the newly introduced species will be in some way beneficial to humans in its new location or, (2) species are introduced intentionally but with no regard to

1680-710: A subgroup of seriates, are famous for their ability to regenerate if divided by cuts across their bodies. Experiments show that (in fragments that do not already have a head) a new head grows most quickly on those fragments which were originally located closest to the original head. This suggests the growth of a head 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 . The vast majority of turbellarians are hermaphrodites (they have both female and male reproductive cells) which fertilize eggs internally by copulation . Some of

1764-481: Is a syncitium , which is a layer of cells that shares a single external membrane . Trematodes are divided into two groups, Digenea and Aspidogastrea (also known as Aspodibothrea). These are often called flukes, as most have flat rhomboid shapes like that of a flounder (Old English flóc ). There are about 11,000 species, more than all other platyhelminthes combined, and second only to roundworms among parasites on metazoans . Adults usually have two holdfasts:

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1848-528: Is highly variable. Some have a substantial negative effect on a local ecosystem (in which case they are also classified more specifically as an invasive species ), while other introduced species may have little or no negative impact (no invasiveness), and integrate well into the ecosystem they have been introduced to. Some species have been introduced intentionally to combat pests. They are called biocontrols and may be regarded as beneficial as an alternative to pesticides in agriculture for example. In some instances

1932-488: Is likely to cause economic or environmental harm or harm to human health". The biological definition of invasive species, on the other hand, makes no reference to the harm they may cause, only to the fact that they spread beyond the area of original introduction. Some argue that "invasive" is a loaded word and harm is difficult to define. From a regulatory perspective, it is neither desirable nor practical to list as undesirable or outright ban all non-native species (although

2016-530: Is needed to keep the body fluids at the right concentration. These combinations of flame cells and tube cells are called protonephridia . In all platyhelminths, the nervous system is concentrated at the head end. Other platyhelminths have rings of ganglia in the head and main nerve trunks running along their bodies. Early 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 proposed

2100-493: Is seldom understood in the beginning, and many non-native ornamentals languish in the trade for years before suddenly naturalizing and becoming invasive. Studies have shown that introduced species display a greater likeliness of naturalizing when there is an appropriate environmental match, the plant species are short lived herbs or cultivate from seeds. Peaches , for example, originated in China, and have been carried to much of

2184-575: Is the European rabbit in Australia . Thomas Austin , a British landowner, had rabbits released on his estate in Victoria because he missed hunting them. A more recent example is the introduction of the common wall lizard ( Podarcis muralis) to North America by a Cincinnati boy, George Rau, around 1950 after a family vacation to Italy . Intentional introductions have also been undertaken with

2268-593: Is the seaweed Caulerpa taxifolia . Caulerpa was first observed in the Mediterranean Sea in 1984, off the coast of Monaco . By 1997, it had covered some 50 km . It has a strong potential to overgrow natural biotopes , and represents a major risk for sublittoral ecosystems . The origin of the alga in the Mediterranean was thought to be either as a migration through the Suez Canal from

2352-859: Is the reintroduction of a species that has become locally endangered or extinct, done in the interests of conservation. Examples of successful reintroductions include wolves to Yellowstone National Park in the U.S., and the red kite to parts of England and Scotland. Introductions or translocations of species have also been proposed in the interest of genetic conservation , which advocates the introduction of new individuals into genetically depauperate populations of endangered or threatened species. Unintentional introductions occur when species are transported by human vectors. Increasing rates of human travel are providing accelerating opportunities for species to be accidentally transported into areas in which they are not considered native. For example, three species of rat (the black, Norway and Polynesian) have spread to most of

2436-551: Is the small Indian mongoose ( Urva auropunctata ). Originating in a region encompassing Iran and India , it was introduced to the West Indies and Hawaii in the late 1800s for pest control. Since then, it has thrived on prey unequipped to deal with its speed, nearly leading to the local extinction of a variety of species. In some cases, introduced animals may unintentionally promote the cause of rewilding . For example, escaped horses and donkeys that have gone feral in

2520-594: The American bison and the turkey are non-native species to North America. Collectively, non-native crops and livestock account for 98% of US food. These and other benefits from non-natives are so vast that, according to the Congressional Research Service, they probably exceed the costs. Other examples of species introduced for the purposes of benefiting agriculture , aquaculture or other economic activities are widespread. Eurasian carp

2604-684: The Australian Dung Beetle Project in an effort to reduce the impact of livestock manure. The timber industry promoted the introduction of Monterey pine ( Pinus radiata ) from California to Australia and New Zealand as a commercial timber crop. These examples represent only a small subsample of species that have been moved by humans for economic interests. The rise in the use of genetically modified organisms has added another potential economic advantage to introducing new/modified species into different environments. Companies such as Monsanto that earn much of their profit through

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2688-553: The Cuban tree frog , and potentially the Venezuela snouted tree frog were introduced with the former two becoming established. Most accidentally or intentionally introduced species do not become invasive as the ones mentioned above. For instance, Some 179 coccinellid species have been introduced to the U.S. and Canada; about 27 of these non-native species have become established, and only a handful can be considered invasive, including

2772-560: The State of Hawaii has adopted an approach that comes close to this). Regulations require a definitional distinction between non-natives that are deemed especially onerous and all others. Introduced "pest" species, that are officially listed as invasive, best fit the definition of an invasive species. Early detection and rapid response is the most effective strategy for regulating a pest species and reducing economic and environmental impacts of an introduction. Management of invasion pathways are on

2856-580: The cane toad and red fox in Australia , nutria in North America , Eurasia , and Africa , and the common brushtail possum in New Zealand . In Taiwan , the success of introduced bird species was related to their native range size and body size; larger species with larger native range sizes were found to have larger introduced range sizes. One notoriously devastating introduced species

2940-689: The imported giant African snail Achatina fulica , which was displacing native snails. However, these planarians are themselves a serious threat to native snails and should not be used for biological control. In northwest Europe , there are concerns about the spread of the New Zealand planarian Arthurdendyus triangulatus , which preys on earthworms . Platyhelminthes are bilaterally symmetrical animals : their left and right sides are mirror images of each other; this also implies they have distinct top and bottom surfaces and distinct head and tail ends. Like other bilaterians , they have three main cell layers (endoderm, mesoderm , and ectoderm ), while

3024-648: The phylogenetic tree : Acoelomorpha [REDACTED] Deuterostomia [REDACTED] Ecdysozoa [REDACTED] Gnathifera [REDACTED] Gastrotricha [REDACTED] Platyhelminthes [REDACTED] Mollusca [REDACTED] Annelida [REDACTED] The internal relationships of Platyhelminthes are shown below. The tree is not fully resolved. Catenulida Haplopharyngida Macrostomida Prorhynchida Polycladida Gnosonesimida Kalyptorhynchia Dalytyphloplanida Proseriata Prolecithophora Fecampiida Introduced species The impact of introduced species

3108-484: The radially symmetrical cnidarians and ctenophores (comb jellies) have only two cell layers. Beyond that, they are "defined more by what they do not have than by any particular series of specializations." Unlike most other bilaterians, Platyhelminthes have no internal body cavity, so are described as acoelomates . Although the absence of a coelom also occurs in other bilaterians: gnathostomulids , gastrotrichs , xenacoelomorphs , cycliophorans , entoproctans and

3192-573: The Americas may play ecological roles similar to those of the equids that became extinct there at the end of the Pleistocene . The exotic pet trade has also been a large source of introduced species. The species favored as pets have more general habitat requirements and larger distributions. Therefore, as these pets escape or are released, unintentionally or intentionally, they are more likely to survive and establish non-native populations in

3276-697: The Indian subcontinent and is impacting a range of wild species including urban birds. Most introduced species do not become invasive. Examples of introduced animals that have become invasive include the gypsy moth in eastern North America , the zebra mussel and alewife in the Great Lakes , the Canada goose and gray squirrel in Europe, the beaver in Tierra del Fuego , the muskrat in Europe and Asia ,

3360-433: The Mediterranean region, where it can form monocultures that threaten critical conservation habitats. Japanese knotweed grows profusely in many nations. Human beings introduced it into many places in the 19th century. It is a source of resveratrol , a dietary supplement. It can grow in building foundations, threatening their stability, and spreads quite quickly. Mesquite ( Prosopis juliflora ) has spread very widely across

3444-681: The Red Sea, or as an accidental introduction from an aquarium. Another troublesome plant species is the terrestrial plant Phyla canescens , which was intentionally introduced into many countries in North America, Europe, and Africa as an ornamental plant. This species has become invasive in Australia, where it threatens native rare plants and causes erosion and soil slumping around river banks. It has also become invasive in France where it has been listed as an invasive plant species of concern in

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3528-490: The adult form after attaching to a suitable host. Because they do not have internal body cavities , Platyhelminthes were regarded as 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 have separated out one subgroup, the Acoelomorpha , as basal bilaterians – closer to the original bilaterians than to any other modern groups. The remaining Platyhelminthes form

3612-436: The aim of ameliorating environmental problems. A number of fast spreading plants such as kudzu have been introduced as a means of erosion control. Other species have been introduced as biological control agents to control invasive species . This involves the purposeful introduction of a natural enemy of the target species with the intention of reducing its numbers or controlling its spread. A special case of introduction

3696-399: The brain, mounted on tentacles, or spaced uniformly around the edge of the body. The ocelli can only distinguish the direction from which light is coming to enable the animals to avoid it. A few groups have statocysts - fluid-filled chambers containing a small, solid particle or, in a few groups, two. These statocysts are thought to function as balance and acceleration sensors, as they perform

3780-532: The broadest and most widely used sense, an introduced species is synonymous with "non-native" and therefore applies as well to most garden and farm organisms; these adequately fit the basic definition given above. However, some sources add to that basic definition "and are now reproducing in the wild", which means that species growing in a garden, farm, or house may not meet the criteria unless they escape and persist. There are many terms associated with introduced species that represent subsets of introduced species, and

3864-477: The devastating tropical disease bilharzia , also belong to this group. Adults range between 0.2 mm (0.0079 in) and 6 mm (0.24 in) in length. Individual adult digeneans are of a single sex, and in some species slender females live in enclosed grooves that run along the bodies of the males, partially emerging to lay eggs. In all species the adults have complex reproductive systems, capable of producing between 10,000 and 100,000 times as many eggs as

3948-461: 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, and then release eggs. Unlike the other parasitic groups, the monogeneans are external parasites infesting aquatic animals , and their larvae metamorphose into

4032-539: The economy. There have been calls from scientists to consider a species "invasive" only in terms of their spread and reproduction rather than the harm they may cause. According to a practical definition, an invasive species is one that has been introduced and become a pest in its new location, spreading (invading) by natural means. The term is used to imply both a sense of urgency and actual or potential harm. For example, U.S. Executive Order 13112 (1999) defines "invasive species" as "an alien species whose introduction does or

4116-585: The ecosystems they enter into, there are still some species that have affected the ecosystem in a positive way. For example, in New Hampshire invasive plants can provide some benefits to some species. Invasive species such as autumn olive, oriental bittersweet, and honeysuckle produce fruit that is used by a handful of fruit-eating bird species. The invasive plants can also be a source of pollen and nectar for many insects, such as bees. These invasive plants were able to help their ecosystem thriving, and increase

4200-429: The external syncytium absorbs dissolved nutrients from the host. Adult digeneans can live without oxygen for long periods. Members of this small group have either a single divided sucker or a row of suckers that cover the underside. They infest the guts of bony or cartilaginous fish, turtles, or the body cavities of marine and freshwater bivalves and gastropods . Their eggs produce ciliated swimming larvae, and

4284-473: The forefront of eliminating unwanted invasive species this would include preliminary steps; educating the public, cooperation from industries and government resources. In Great Britain , the Wildlife and Countryside Act 1981 prevents the introduction of any animal not naturally occurring in the wild or any of a list of both animals or plants introduced previously and proved to be invasive. By definition ,

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4368-509: The gut or pharynx (throat). All animals need to keep 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 high concentrations of dissolved material, and generally let their tissues have the same level of concentration as the environment, while freshwater animals need to prevent their body fluids from becoming too dilute. Despite this difference in environments, most platyhelminths use

4452-442: The host, and also disguises it chemically to avoid attacks by the host's immune system . Shortage of carbohydrates in the host's diet stunts the growth of parasites and may even kill them. Their metabolisms generally use simple but inefficient chemical processes, compensating for this inefficiency by consuming large amounts of food relative to their physical size. In the majority of species, known as eucestodes ("true tapeworms"),

4536-531: The hosts' skins. The name "Monogenea" is based on the fact that these parasites have only one nonlarval generation. These are often called tapeworms because of their flat, slender but very long bodies – the name " cestode " is derived from the Latin word cestus , which means "tape". The adults of all 3,400 cestode species are internal parasites. Cestodes have no mouths or guts, and the syncitial skin absorbs nutrients – mainly carbohydrates and amino acids – from

4620-586: The intentionally introduced Harmonia axyridis , multicolored Asian lady beetle . However the small percentage of introduced species that become invasive can produce profound ecological changes. In North America, Harmonia axyridis has become the most abundant lady beetle and probably accounts for more observations than all the native lady beetles put together. Many non-native plants have been introduced into new territories, initially as either ornamental plants or for erosion control, stock feed, or forestry. Whether an exotic will become an invasive species

4704-849: The introduction of common starlings to North America by the American Eugene Schieffelin , a lover of the works of Shakespeare and the chairman of the American Acclimatization Society , who, it is rumoured, wanted to introduce all of the birds mentioned in Shakespeare's plays into the United States. He deliberately released eighty starlings into Central Park in New York City in 1890, and another forty in 1891. Yet another prominent example of an introduced species that became invasive

4788-489: The invasive comb jelly Mnemiopsis leidyi , the dangerous bacterium Vibrio cholerae , or the fouling zebra mussel . The Mediterranean and Black Seas, with their high volume shipping from exotic sources, are most impacted by this problem. Busy harbors are all potential hotspots as well: over 200 species have been introduced to the San Francisco Bay in this manner making it the most heavily invaded estuary in

4872-561: The large species have flat ribbon-like or leaf-like shapes. Because there is no circulatory system which can transport nutrients around, the guts of large species have many branches, allowing the nutrients to diffuse to all parts of the body. 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 as leaf litter or between grains of soil, and as parasites within other animals. The space between

4956-463: 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. In most species, "miniature adults" emerge when the eggs hatch, but a few large species produce plankton -like larvae . These parasites' name refers to the cavities in their holdfasts (Greek τρῆμα, hole), which resemble suckers and anchor them within their hosts. The skin of all species

5040-459: The life cycle has one or two hosts. Cercomeromorpha contains parasites attach themselves to their hosts by means of disks that bear crescent-shaped hooks. They are divided into the Monogenea and Cestoda groupings. Of about 1,100 species of monogeneans , most are external parasites that require particular host species - mainly fish, but in some cases amphibians or aquatic reptiles. However,

5124-475: The mouth. The genus Paracatenula , whose members include tiny flatworms living in symbiosis with bacteria, is even missing a mouth and a gut. However, some long species have an anus and some with complex, branched guts have more than one anus, since excretion only through the mouth would be difficult for them. The gut is lined with a single layer of endodermal cells that absorb and digest food. Some species break up and soften food first by secreting enzymes in

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5208-547: The native animal's chances of survival. Several introduced exotic trees served as nest sites for resident waterbird species in Udaipur city, India. Perhaps the most common motivation for introducing a species into a new place is that of economic gain. Non-native species can become such a common part of an environment, culture, and even diet that little thought is given to their geographic origin. For example, soybeans , kiwi fruit , wheat , honey bees , and all livestock except

5292-439: The neck produces a chain of segments called proglottids via a process known as strobilation . As a result, the most mature proglottids are furthest from the scolex. Adults of Taenia saginata , which infests humans, can form proglottid chains over 20 metres (66 ft) long, although 4 metres (13 ft) is more typical. Each proglottid has both male and female reproductive organs. If the host's gut contains two or more adults of

5376-459: The new environment. Adventive species are often considered synonymous with "introduced species", but this term is sometimes applied exclusively to introduced species that are not permanently established. Naturalized species are often introduced species that do not need human help to reproduce and maintain their population in an area outside their native range (no longer adventive), but that also applies to populations migrating and establishing in

5460-517: The number of native iguanas on multiple islands. In plants, introduced species have been observed to undergo rapid evolutionary change to adapt to their new environments, with changes in plant height, size, leaf shape, dispersal ability, reproductive output, vegetative reproduction ability, level of dependence on the mycorrhizal network , and level of phenotype plasticity appearing on timescales of decades to centuries. It has been hypothesized that invasive species of microbial life could contaminate

5544-420: The parasites from one host to another. The definitive host in which adults develop is a land vertebrate; the earliest host of juvenile stages is usually a snail that may live on land or in water, whilst in many cases, a fish or arthropod is the second host. 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

5628-455: The parastic mesozoans . They also lack specialized circulatory and respiratory organs, both of these facts are defining features when classifying a flatworm's anatomy . Their bodies are soft and unsegmented. 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

5712-431: The place of introduction and cause damage to nearby species, they are called " invasive species ". The transition from introduction, to establishment and to invasion has been described in the context of plants. Introduced species are essentially "non-native" species. Invasive species are those introduced species that spread widely or quickly and cause harm, be that to the environment, human health, other valued resources, or

5796-778: The populated world. Tomatoes are native to the Andes . Squash ( pumpkins ), maize (corn), and tobacco are native to the Americas , but were introduced to the Old World . Many introduced species require continued human intervention to survive in the new environment. Others may become feral, but do not seriously compete with natives, but simply increase the biodiversity of the area. One example would be Dandelions in North America , which have become an essential source of early season nectar for both native and introduced pollinators, and do not meaningfully compete with native grasses or flowers. A very troublesome marine species in southern Europe

5880-572: The potential for being beneficial or detrimental in the long run remains unknown. The effects of introduced species on natural environments have gained much scrutiny from scientists, governments, farmers and others. The formal definition of an introduced species from the United States Environmental Protection Agency is "A species that has been intentionally or inadvertently brought into a region or area. Also called an exotic or non-native species". In

5964-436: The potential impact. Unintentional or accidental introductions are most often a byproduct of human movements and are thus unbound to human motivations. Subsequent range expansion of introduced species may or may not involve human activity. Species that humans intentionally transport to new regions can subsequently become successfully established in two ways. In the first case, organisms are purposely released for establishment in

6048-464: The purposes of sport fishing and hunting. The introduced amphibian ( Ambystoma tigrinum ) that threatens the endemic California salamander ( A. californiense ) was introduced to California as a source of bait for fishermen. Pet animals have also been frequently transported into new areas by humans, and their escapes have resulted in several introductions, such as feral cats , parrots , and pond slider . Lophura nycthemera ( silver pheasant ),

6132-618: 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 by the host. The eucestode life cycle is less complex than that of digeneans , but varies depending on the species. For example: Members of the smaller group known as Cestodaria have no scolex, do not produce proglottids, and have body shapes similar to those of diageneans. Cestodarians parasitize fish and turtles. The relationships of Platyhelminthes to other Bilateria are shown in

6216-495: The same system to control the concentration of their body fluids. Flame cells , so called because 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 it into networks of tube cells which are lined with flagella and microvilli . The tube cells' flagella drive the water towards exits called nephridiopores , while their microvilli reabsorb reusable materials and as much water as

6300-425: The same way in cnidarian medusae and in ctenophores . However, turbellarian statocysts have no sensory cilia, so the way they sense the movements and positions of solid particles is unknown. On the other hand, most have ciliated touch-sensor cells scattered over their bodies, especially on tentacles and around the edges. Specialized cells in pits or grooves on the head are most likely smell sensors. Planarians ,

6384-519: The selling of genetically modified seeds has added to the controversy surrounding introduced species. The effect of genetically modified organisms varies from organism to organism and is still being researched today, however, the rise of genetically modified organisms has added complexity to the conversations surrounding introduced species. Introductions have also been important in supporting recreation activities or otherwise increasing human enjoyment. Numerous fish and game animals have been introduced for

6468-658: The skin 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 type of skeleton , providing attachment points for muscles . The mesenchyme contains all the internal organs and allows the passage of oxygen, nutrients and waste products. It consists of two main types of cell: fixed cells, some of which have fluid-filled vacuoles ; and stem cells , which can transform into any other type of cell, and are used in regenerating tissues after injury or asexual reproduction . Most platyhelminths have no anus and regurgitate undigested material through

6552-628: The terminology associated with introduced species is now in flux for various reasons. Examples of these terms are "invasive", "acclimatized", "adventive", "naturalized", and "immigrant" species. The term "invasive" is used to describe introduced species that cause ecological, economic, or other damage to the area in which they were introduced. Acclimatized species are introduced species that have changed physically and/or behaviorally in order to adjust to their new environment. Acclimatized species are not necessarily optimally adjusted to their new environment and may just be physically/behaviorally sufficient for

6636-619: The wild. Among the popular exotic pets that have become alien or invasive species are parrots, frogs, terrapins, and iguanas. Some species, such as the Western honey bee , brown rat , house sparrow , ring-necked pheasant , and European starling , have been introduced very widely. In addition there are some agricultural and pet species that frequently become feral ; these include rabbits , dogs , ducks , snakes , goats , fish , pigs , and cats . Many water fleas such as Daphnia , Bosmina and Bythotrephes have introduced around

6720-423: The wild. It is sometimes difficult to predict whether a species will become established upon release, and if not initially successful, humans have made repeated introductions to improve the probability that the species will survive and eventually reproduce in the wild. In these cases, it is clear that the introduction is directly facilitated by human desires. In the second case, species intentionally transported into

6804-427: The world as hitchhikers on ships, and arachnids such as scorpions and exotic spiders are sometimes transported to areas far beyond their native range by riding in shipments of tropical fruit. This was seen during the introduction of Steatoda nobilis (Noble false widow) worldwide through banana shipments. Further there are numerous examples of marine organisms being transported in ballast water , among them

6888-431: The world, causing dramatic changes in native freshwater ecosystems. When a new species is introduced, the species could potentially breed with members of native species, producing hybrids. The effect of the creating of hybrids can range from having little effect, a negative effect, to having devastating effects on native species. Potential negative effects include hybrids that are less fit for their environment resulting in

6972-603: The world. There is also the accidental release of the Africanized honey bees (AHB), known colloquially as "killer bees") or Africanized bee to Brazil in 1957 and the Asian carp to the United States. The insect commonly known as the brown marmorated stink bug ( Halyomorpha halys ) was introduced accidentally in Pennsylvania. Another form of unintentional introductions is when an intentionally introduced plant carries

7056-534: Was first introduced to the United States as a potential food source. The apple snail was released in Southeast Asia with the intent that it be used as a protein source, and subsequently to places like Hawaii to establish a food industry. In Alaska, foxes were introduced to many islands to create new populations for the fur trade. About twenty species of African and European dung beetles have established themselves in Australia after deliberate introduction by

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