Trematodes, also called flukes, cause various clinical infections in humans. The parasites are so named because of their conspicuous suckers, the organs of attachment (trematos means “pierced with holes”). All the flukes that cause infections in humans belong to the group of digenetic trematodes.
Are trematodes and flukes the same?
Trematoda is a class within the phylum Platyhelminthes. It includes two groups of parasitic flatworms, known as flukes. They are internal parasites of molluscs and vertebrates.
Why are flatworms called flukes?
All trematodes are parasitic flatworms. This term fluke can be traced back to the Saxon name for flounder, and refers to the flattened, rhomboidal shape of the worms.
What does flukes mean in biology?
Flukes are a kind of parasitic flatworm under the class trematoda inside the phylum platyhelminthes. Most trematodes have an intricate life cycle with at least two hosts. The primary host is a vertebrate, where the flukes reproduce sexually. The intermediate host is typically a snail, where asexual reproduction occurs.
Is a trematode a fluke?
fluke, also called blood fluke or trematode, any member of the invertebrate class Trematoda (phylum Platyhelminthes), a group of parasitic flatworms that probably evolved from free-living forms millions of years ago. There are more than 10,000 species of flukes.
What are characteristics of flukes?
Flukes are leaf-shaped, ranging in length from a few millimeters to 7 to 8 cm. The tegument is morphologically and physiologically complex. Flukes possess an oral sucker around the mouth and a ventral sucker or acetabulum that can be used to adhere to host tissues. A body cavity is lacking.
What is the main difference between flukes and flatworms?
Flukes vs TapewormsFlukes belong to the class trematode, and they are leaf-shaped.Tapeworms belong to the class cestode, and they are flat, long worms which reside on the intestines.Reproductive SystemsMost of the flukes are hermaphroditic except blood flukes.All tapeworms are hermaphroditic.10 more rows•Dec 6, 2017
Why is it called fluke?
It could be derived from the “flatfish” sense of “fluke,” perhaps because of a resemblance between the flatness of the fish and the anchor tips. The use of “fluke” to mean a whale's tail comes from the likeness of the tail to the pointed tips of an anchor.
What fluke stands for?
fluke noun (LUCK) something that happens, usually something good, that is the result of chance instead of skill or planning: The first goal was just a fluke.
What is called fluke?
Noun. fluke (plural flukes) A flounder. A trematode; a parasitic flatworm of the Trematoda class, related to the tapeworm. The man had become infected with flukes after eating a meal of raw fish.
How do you identify flukes?
Symptoms of Flukes in FishMissing scales.Red spots.Excess mucus.Hazy look to the skin.Flashing behavior.Lethargy.Decreased appetite.
What is a fluke in parasitology?
Flukes are parasitic flatworms. There are many species of fluke. Different species tend to infect different parts of the body. Flukes may infect. Blood vessels of digestive or urinary system: Schistosoma species (schistosomiasis.
What are the two types of flukes?
The flukes that cause most human infections are Schistosoma species (blood fluke), Paragonimus westermani (lung fluke), and Clonorchis sinensis (liver fluke).
How do flatworms get their name?
Worms in the phylum Platyhelminthes are called flatworms because they have flattened bodies. There are more than 18,500 known species of flatworms.
What is the scientific name for flukes?
TrematodaFlukes / Scientific name
Why flatworms are called parasites?
A number of flatworm species are free-living, but about 80 percent of all flatworms are parasitic—i.e., living on or in another organism and securing nourishment from it.
How did a flatworm get its name?
The flatworms are a phylum, Platyhelminthes, of relatively simple, soft-bodied, bilaterially symmetrical, invertebrate animals. The name of the phylum comes from the Greek platy, meaning "flat," and helminth, meaning "worm," which is indicative of their ribbon-shaped, flattened appearance.
Where are trematodes found?
Trematodes are found around the world. The presence of their host species is often the limiting factor in their geographic distribution. For example, a flatworm that uses a mollusk as its host occurs only where that mollusk lives. Nonetheless, the distribution of a particular trematode can span large areas, particularly if their host species live in a broad range of habitats; or if members of the host species, like birds, are able to run or fly over vast regions.
What is the asexual phase of a digenetic fluke?
Digenetic flukes engage in both asexual and sexual reproduction. When the first-stage larvae reach their destination within the first intermediate host, a polyembryonic asexual reproductive phase begins. After the larvae develop into sporocysts, the sporocysts of some species produce a second generation of sporocysts, while others produce rediae. Trichobilharzia physellae and Diplostomum flexicaudum take the two-generations-of sporocysts route. Metorchis conjunctus and Proterometra dickermani develop from miracidium to sporocyst to redia. A few species, including Stichorchis subtriquetres, go directly from miracidium to redia, bypassing the sporocyst stage altogether. The rediae are also capable of asexual reproduction to produce a second generation of rediae. Via sporocysts and rediae, the number of invading trematodes can multiply very quickly within the first intermediate host.
What is the life cycle of a digenetic trematode?
As described, the life cycle pattern of the digenetic trematodes is quite complex, involving first- and second-stage larvae as well as adults that are dependent on a host species for survival. Upon hatching, the first-stage larvae, known as miracidia, infect the first intermediate host, usually a mollusk. Many miracidia take advantage of light and gravitational cues to reach an area suitable to their hosts, then hone in on an individual host by following its chemical signature, which may be fatty acids or amino acids specific to the organism. Other miracidia, however, seem to stumble upon rather than track their host. In still other trematode species, the egg does not develop until it is eaten by the host species.
What type of worms have holdfast organs?
Trematodes are parasitic flatworms, usually leaflike in appearance, with holdfast organs that they use to adhere to their hosts. Digenetic species typically use muscular, oral and/or. ventral suckers to attach to their hosts. Members of the subclass Aspidogastrea have a large ventral disk that they use for adhesion.
How many hosts does a trematode have?
Digenetic trematodes typically have two larval stages and at least two hosts. Several, including Halipegus occidualis, have four hosts, ending up at the base of the tongue of a green frog ( Rana clamitans ), which is the definitive host of H. occidualis. The life cycles of members of the subclass Aspidogastrea, which sometimes take a shorter path with only one host and no asexually reproducing larvae, are described as direct.
How many species are there in the class Trematoda?
Evolution and systematics. The class Trematoda has about 6,000 species, although the number given varies considerably among different researchers. The class is commonly divided into two subclasses, Aspidogastrea and Digenea.
Where do metacercariae migrate?
The metacercariae migrate to the cecum, small intestine, or rectum, and attach themselves to these organs with oral and ventral suckers. The hermaphrodites mature in the host's digestive tract, engage in self-fertilization, and lay eggs. In the laboratory, adult echinostomes live four to eight weeks.
What are the parasites of trematodes?
The Digenea, the majority of trematodes, are obligate parasites of both mollusks and vertebrates, but rarely occur in cartilaginous fish . Two other parasitic classes, the Monogenea and Cestoda, are sister classes in the Neodermata, a group of Rhabditophoran Platyhelminthes.
Which species exemplifies the remarkable life history of the trematodes?
A species that exemplifies the remarkable life history of the trematodes is the bird fluke, Leucochloridium paradoxum. The definitive hosts, in which the parasite reproduces, are various woodland birds, while the hosts in which the parasite multiplies (intermediate host) are various species of snail.
What is the primary host of a trematode?
Most trematodes have a complex life cycle with at least two hosts. The primary host, where the flukes sexually reproduce, is a vertebrate. The intermediate host, in which asexual reproduction occurs, is usually a snail .
How many species are there in trematodes?
The trematodes or flukes include 18,000 to 24,000 species, divided into two subclasses. Nearly all trematodes are parasites of mollusks and vertebrates. The smaller Aspidogastrea, comprising about 100 species, are obligate parasites of mollusks and may also infect turtles and fish, including cartilaginous fish.
What is the class of trematoda?
Trematoda. Rudolphi, 1808. Subclasses. Aspidogastrea. Digenea. Trematoda is a class within the phylum Platyhelminthes. It includes two groups of parasitic flatworms, known as flukes . They are internal parasites of molluscs and vertebrates. Most trematodes have a complex life cycle with at least two hosts.
How big are trematodes?
Anatomy. Trematodes are flattened oval or worm-like animals, usually no more than a few centimetres in length, although species as small as 1 millimetre (0.039 in) are known. Their most distinctive external feature is the presence of two suckers, one close to the mouth, and the other on the underside of the animal.
Which fully developed form infects the definitive host?
The adult is the fully developed form which infects the definitive host.
Evolution and Systematics
Physical Characteristics
- Trematodes are parasitic flatworms, usually leaflike in appearance, with holdfast organs that they use to adhere to their hosts. Digenetic species typically use muscular, oral and/or ventral suckers to attach to their hosts. Members of the subclass Aspidogastrea have a large ventral disk that they use for adhesion. This disk is covered with many sm...
Distribution
- Trematodes are found around the world. The presence of their host species is often the limiting factorin their geographic distribution. For example, a flatworm that uses a mollusk as its host occurs only where that mollusk lives. Nonetheless, the distribution of a particular trematode can span large areas, particularly if their host species live in a broad range of habitats; or if member…
Habitat
- The habitat of trematodes frequently varies over the course of their lives. Members of the subclass Digenea are endoparasites with indirect life cycles, which means that they infect different hosts during the various stages of their life cycles. Digenetic trematodes typically have two larval stages and at least two hosts. Several, including Halipegus occidualis, have four hosts…
Behavior
- As described, the life cycle pattern of the digenetic trematodes is quite complex, involving first- and second-stage larvae as well as adults that are dependent on a host species for survival. Upon hatching, the first-stage larvae, known as miracidia, infect the first intermediate host, usually a mollusk. Many miracidia take advantage of light and gravitational cues to reach an area suitabl…
Feeding Ecology and Diet
- Trematodes are obligate parasites, which means that they require nourishment from a host organism. Adult digenetic trematodes die soon after removal from the host, while members of Aspidogastrea may survive independently for a month or more. Digenetic trematode first-stage larvae, or miracidia, do not feed. For this reason, they must find a first intermediate host very qui…
Reproductive Biology
- Digenetic flukes engage in both asexual and sexual reproduction. When the first-stage larvae reach their destination within the first intermediate host, a polyembryonic asexual reproductive phase begins. After the larvae develop into sporocysts, the sporocysts of some species produce a second generation of sporocysts, while others produce rediae. Trichobilharzia physellae and Dip…
Significance to Humans
- Trematodes pose a significant health threat to humans, particularly those living in developing countries. A common illness in developing countries is schistosomiasis. This condition, caused by three species of Schistosoma, affects more than 40 million individuals who live in tropical and subtropical countries, causing weakness, diarrhea, hemorrhage, fever, enlargement of the spleen…
Species Accounts
- No common name
Rugogaster hydrolagi - Echinostome
Echinostoma revolutum
Resources
- Books
Doss, Mildred A. Index Catalogue of Medical and Veterinary Zoology: Trematoda,Parts 1–8. Washington, DC: U. S. Government Printing Office, 1966. Olsen, O. Wilford. Animal Parasites: Their Biology and Life Cycles.Minneapolis: Burgess Publishing Co., 1967. Schell, Stewart C. How to Kn… - Periodicals
Combes, C., A. Fournier, H. Moné, and A. Théron. "Behaviours in Trematode Cercariae That Enhance Parasite Transmission: Patterns and Processes." Parasitology109 (1994): S3–S13. Esch, G. W., M. A. Barger, and K. Joel Fellis. The Transmission of Digenetic Trematodes: Style, Eleganc…
Overview
Trematoda is a class within the phylum Platyhelminthes. It includes two groups of parasitic flatworms, known as flukes.
They are internal parasites of molluscs and vertebrates. Most trematodes have a complex life cycle with at least two hosts. The primary host, where the flukes sexually reproduce, is a vertebrate. The intermediate host, in which asexual rep…
Anatomy
Trematodes are flattened oval or worm-like animals, usually no more than a few centimeters in length, although species as small as 1 millimetre (0.039 in) are known. Their most distinctive external feature is the presence of two suckers, one close to the mouth, and the other on the underside of the animal.
The body surface of trematodes comprises a tough syncytial tegument, which …
Taxonomy and biodiversity
The trematodes or flukes include 18,000 to 24,000 species, divided into two subclasses. Nearly all trematodes are parasites of mollusks and vertebrates. The smaller Aspidogastrea, comprising about 100 species, are obligate parasites of mollusks and may also infect turtles and fish, including cartilaginous fish. The Digenea, the majority of trematodes, are obligate parasites of both mollusks and vertebrates, but rarely occur in cartilaginous fish.
Organ morphology
Body wall musculature: Formed of three different muscle layers: circular, longitudinal, and diagonal. The outermost layer is formed by the circular muscle fibers, directly behind that are the longitudinal muscle fibers. The inner layer is formed by the diagonal muscle fibers. Together these muscle fibers form the segmented body wall of trematodes.
Oral sucker and acetabulum: In some species of Trematoda, such as T. bragai, there is an acetab…
Life cycles
Trematodes have a very complex life cycle and depending on what taxa they belong to, their life cycles can be completed with as little as one host compared to the typical three hosts. When there is one host, this is normally a specific species of snail of the family Lymnaeidae. Almost all trematodes infect molluscs as the first host in the life cycle, and most have a complex life cycle involving other hosts. Most trematodes are monoecious and alternately reproduce sexually and a…
Infections
Human infections are most common in Asia, Africa and Latin America. However, trematodes can be found anywhere where untreated human waste is used as fertilizer. Humans can be infected by trematodes either by consuming undercooked contaminated fish or plants, or by ingesting contaminated water. The metacercariae of trematodes attach to fish and plants. In addition, humans can be infected by certain species through swimming in contaminated water. Humans …
Etymology
Trematodes are commonly referred to as flukes. This term can be traced back to the Old English name for flounder, and refers to the flattened, rhomboidal shape of the worms.
The flukes can be classified into two groups based on, on the basis of the system in which they infect their in the vertebrate host.
They may also be classified according to the environment in which they are found. For instance, …
External links
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