Definition: What are Trematodes?

Also known as flukes, trematodes space a group of helminth flatworms (leaf-shaped). Return they room mostly linked with such aquatic fauna as fish and also mollusks, they also impact various vertebrates as component of their indirect life cycle.

They space organisms the veterinary and also medical prominence (given the they epidemic and impact both person beings and animals). Through over 20,000 species in the class Trematoda, trematodes deserve to be uncovered in various habitats throughout the globe.

Depending on the species, trematodes might depend ~ above one or number of hosts to complete their life cycle.

You are watching: Trematodes belong to the phylum ___________.


Some examples of trematodes include:


S. JaponicumS. HaematobiumP. HeterotremusF. HepaticaC. SinensisP. WestermaniS. Hematobium


4 Schistosoma mansoni trematodes.Far left-thinner female cradled inside thicker masculine worm"s gynecophoral canal.Center is solitary thin woman worm,right is an ext robust,thicker masculine S. Mansoni by CDC



· Kingdom: Animalia - As part of this kingdom, trematodes consume essential material, usage oxygen (when it is available), are capable of movement and can reproduce and also grow.


· Phylum: Platyhelminthes - Trematodes belong to the phylum Platyhelminthes (flatworms) and thus characterized by bilateral symmetry.


· Orders: Monogenea and Digenea - Obligate parasites


* There space over 20,000 types of Trematoda that can be divided into about 2,200 basic and about 256 families.


While different trematode varieties may possess attributes that are lacking in others, castle share a variety of morphological features. Because that instance, like many platyhelminths, trematodes are defined by dorsoventrally flattened (unsegmented) bodies that room bilaterally symmetrical. They have a leaf-shaped body.

These space characteristics particularly used to define various trematode species. While a bulk of types are small, only measuring a few millimeters in length, some species can thrive to up to 10 centimeters long.

While they have actually a morphologically and also physiologically complicated tegument (body covering), trematodes carry out not have actually a body cavity. As a result, your organs space bound in parenchyma if the somatic muscle great in the parenchyma connect to the tegument.

However, they have actually a well-developed (and branched) alimentary canal that is composed of one esophagus and also muscular pharynx. Regardless of being fine developed, the intestine walk not open out v an anus. Rather, the two branches run right into a typical pore (excretory vesicle) located at the posterior end of the organism.


* The alimentary canal that trematodes is extended by a solitary layer the epithelial cells.

* Depending on the species, trematodes might have second or tertiary branches of the intestine.

* Apart from lacking a body cavity, trematodes also lack a respiratory tract system.


For attachment purposes, adult trematodes own two specialized suckers. Among these suckers is located about the mouth area/opening if the other is situated in the middle component of the body. These permit trematodes to stay attached to your host.

Using the powerful muscular pharynx that makes up the mouth part, trematodes (both the larvae and adult stages) room able to suck food from the hold as they remain attached making use of both the posterior and ventral suckers. Here, the muscular structures role as powerful pumps that suck blood native the organize as a resource of nutrition (which causes harm come the host).


* Whereas the oral sucker that trematodes contributes to the feeding process, the ventral sucker is just for attachments purposes.


As mentioned, the branched alimentary canal of trematodes go not open up in one anal opening, because that this reason, waste assets are excreted with the mouth opening from the excretory vesicle.


With regards come reproduction, a majority of trematodes have been displayed to it is in hermaphroditic. Together such, an individual has actually both the male and female reproductive organs.

Here, the male reproductive system consists of:


Two testesAccessory glandsA cirrus (acts as the penile part)



The female reproductive system consists of:


An ovarySeminal receptacleYolk glandsOotypeOviduct


While the majority of trematodes are hermaphroditic and use self-fertilization to reproduce, castle have also been presented to reproduce through cross-fertilization. Here, one individual is qualified of fertilizing another.

Depending top top the species, the larval phase goes through several stages of breakthrough before getting to maturity. This may happen in different hosts from aquatic biology to vertebrates.


* Blood flukes are not hermaphroditic and thus do not own both the male and also female reproductive organs.

* The egg of trematodes are identified by a hard and also smooth covering that is yellow-brown in color. The eggs may likewise have spines and vary from 30 to 175 microns depending upon the species.

A paired couple of Schistosoma mansoni through علاء - own work, CC BY-SA 4.0,

Aspidogastrea and Digenean Trematodes

Aspidogastrea and also digenean trematodes comprise the two significant groups that Trematoda. The two groups are distinguished based upon their structures and advancement process.


Although they are still defined as monogenean trematodes in some books today, research studies have displayed that monogenea space not really trematodes. Rather, they space a phylogenetically distinctive group of platyhelminths the are defined by a posterior holdfast organ well-known as the opisthaptor they usage for anchorage.

Most of the types in this team are fish parasites however some types have been found to epidemic turtles.

Digenean Trematodes

The sub-class Digenea is the largest group of helminth Platyhelminthes. Like numerous of the other platyhelminths, digeneans are endoparasites and also thus found inside the body of the host.

Their complex life cycle is dependency on different species of pets including every vertebrates and most the the invertebrates discovered on land, freshwater as well as marine environments. While Digenean trematodes are parasitic in nature, studies have them to it is in free-living in 2 stages of your life cycle. These include the miracidium and cercaria larval stages.

Morphologically, Digenea is defined by an oval, dorso-ventrally flattened body. They additionally have a smooth surface ar with spines and also anterior and ventral suckers. Because that Digenea, both suckers are supplied for attachment and locomotion purposes.

Like the various other trematodes, Digenea likewise have a mouth opening as well as a branched intestine. Because that the many part, Digenea room hermaphrodites with some types having a copulatory organ.


* Digenea consists of end 18,000 nominal species divided right into 150 families.

* Life bicycle starts in aquatic environments, proceeds in semi-aquatic environments and ends in terrestrial environments.

* In human beings, they cause such diseases as schistosomiasis.


As compared to Digenea, Aspidogastrea is a smaller team composed of around 80 varieties of trematodes. Back they space parasites of assorted aquatic organisms consisting of mollusks and also vertebrates, Aspidogastrea have actually a less complicated life-cycle limited to mollusk and also a vertebrate host (facultative or compulsory).

Like Digenea, Aspidogastrea are also endoparasites. Castle are identified by a holdfast organ that lacks a hook extending the ventral side, a row of suckers as well as tegument consist of of microtubercles. The adhesive disc is created of between 3 and 4 rows the alveoli.

Some that the other facets that characterize Aspidogastrea include:


· Larvae own posterior suckers. Castle may likewise have a false, anterior sucker.

· In adults, posterior and also ventral suckers are changed by the adhesive disk the is marked by transverse grooves.

· They differ in length from a couple of millimeters to several centimeters.

Nervous System

Trematodes have actually a primitive nervous device that consists of two ganglia ~ above either next of the esophagus. The pair is associated to each various other through a nerve ring that goes around the esophagus. Except this simple system trematodes do not have any extr sensory organs as is the situation with flatworms.

Reproduction and Life Cycle

Life cycle stages of digenean human parasite, Schistosoma japonicum by Jack,derived indigenous File:Schistosomiasis Life Cycle.png,Public Domain,

As mentioned, a majority of trematodes room hermaphrodites which way that people possess both male and female reproductive organs. This provides self and also cross-fertilization feasible and so can fertilize themselves and each other. 

Apart from sexual reproduction, trematodes are additionally capable that asexual reproduction at offered stages in your life cycle. This section will focus on the life bicycle of Liver flukes (to stand for trematodes) offered that they deserve to reproduce sexually and also asexually and also depend on numerous hosts to finish their life cycle.


* As the surname suggests. Liver fluke parasitizes the liver of assorted mammals. However, castle can additionally be uncovered in the gallbladder and bile ducts of these animals.


The life bike of liver flukes choose Fasciola hepatica starts when eggs to adjust in the bile ducts of a mammal (man, pigs, cows, etc) room released right into the environment with the feces. In aquatic or an extremely damp environments, the eggs build to embryos within a period of three weeks.

The egg hatch in favorable problems of between 10°C and 15°C. The embryo (also well-known as miracidium) own cilia for this reason are qualified of swimming. This permits them come swim in their atmosphere in find of a favorable host.

For Fasciola hepatica, mollusks in aquatic environments are an ideal hosts. They act together intermediate hosts for the larval step of the liver fluke.


* one intermediate hold refers come a host that support the breakthrough of the immature parasites (larvae etc). Few of the helminth in this state are likewise incapable of reproduction.

* The ciliated embryo might swim for several hrs in find of an intermediate host.

In the intermediate hold (the snail) the larvae walk through numerous stages the proliferation (asexually) and also develop into cercariae. Typically, in the asexual phase, the larval will shed their hair-like fibers and also develop into a new larval form. The brand-new larvae also goes through more asexual proliferation/development in ~ the intermediate host where they construct into cercariae.


* Miracidia that enter the snail experience asexual proliferation to create cercariae.


The brand-new larvae (cercariae) pipeline the intermediate hold through that is pulmonary cavity and migrate to wet herbaceous vegetation (e.g. Grass) whereby they encyst to form metacercariae. In this state, the metacercariae can survive miscellaneous harsh environmental problems for numerous months because the tough outer extending protects the organism.


* Metacercariae which is a cyst kind is one infective phase to mammals.


Mammals, which room the definitive hold of the parasite room infected as soon as they ingest the metacercariae. This an especially affects such animals as cows and sheep that have tendency to feeding on vegetation.

Although person beings have actually been presented to be reservoir of the parasite, studies have actually concluded that for Fasciola hepatica, humans are no the right definitive host.

Following ingestion, the metacercariae excyst in the intestine (duodenum) from whereby they move to the peritoneal cavity through the minister wall. At this stage, the parasite is tho immature. It"s only when they with the biliary ducts the they mature and also develop to come to be adults.


* Human beings are likely to it is in infected (Human fascioliasis) by ingesting contaminated plants in damp conditions or life fresh delivering the infective stage of the parasite.


Like a bulk of the various other trematodes, liver flukes (Fasciola Hepatica in this case) space hermaphrodites. Together such, they have both male and also female reproductive systems. Within the biliary ducts, this permits them come self-fertilize (as well together cross-fertilization) in order to develop fertilized eggs.

In the situation of cross-fertilization, copulation is followed by the insertion the the cirrus of one trematode right into the Laurer"s canal the another. This permits for sperm cells to it is in deposited into the oviduct the one parasite for fertilization come occur.

This is different from self-fertilization wherein sperm cells from the exact same individual are released right into the female reproductive system to fertilize the eggs within the oviduct.


Fertilized eggs, which room oval and also brown in color, space then excreted through the feces and the bike continues.

Some of the most usual infections resulted in by trematodes include:




Cestodes Vs. Trematodes

Like trematodes, cestodes (tapeworms) belong come the phylum Platyhelminthes.

They share a variety of similarities including being multicellular, bilateral symmetry, gift endoparasites, as well as lacking a body cavity. When they have actually a number of similarities, the two additionally have miscellaneous differences. These are evident in their mode of reproduction, life cycle, and morphology amongst others.

Unlike trematodes that deserve to be uncovered in mollusks in your larval stages, tapeworms/cestodes have the right to be found in vertebrates. In the host, cestodes like tapeworms acquire nutrients through absorption offered that they execute not have actually a digestive tract and also so nutrients are soaked up through the surface of their body. This is various from trematodes that use their muscular mouth opened to suck blood from the host.

Whereas cestodes possess hooks through which they affix onto the wall surfaces of the hold (in the intestine) trematodes usage suckers that might be anterially or ventrally positioned.

In trematodes, however, this may likewise be provided for movement. Unlike trematodes, the bodies of cestodes room segmented into sections recognized as proglottids. This segments prosper from the scolex (head an ar of cestodes) and also may rest off.

Each of these segments has both male and also female reproductive guts that allow them come self-fertilize. If cestodes are qualified of self-fertilization, like trematodes, trematodes perform not have segmented body attached come a scolex.

When the eggs room released indigenous the hind segments, they are excreted to the aquatic environment from wherein they may be spend by other mammals or fish in which allows their life bike to continue when they space consumed by man.

This is different from the life cycle of miscellaneous trematodes that strictly calls for aquatic intermediate master such as mollusks because that the larval step to develop.

In mammal hosts, tapeworms space confined come the intestine wherein they attain nourishment and also produce eggs. This is no the instance with trematodes that deserve to be found in various other body organs consisting of the lungs, blood and bile ducts (these being in addition to the intestine).

Some that the other differences in between the 2 include:


· Trematodes have actually a more complex life cycle.

· The eggs of trematodes space ciliated which enables for motion in aquatic settings (to with the intermediate host).

· Cestodes have a tubular morphology and also are much longer in length while trematodes are smaller with a leaf-like morphology.

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Barbara L. Doughty. (1996). Chapter 88Schistosomes and also Other Trematodes. Medical Microbiology. Fourth edition.


Katarzyna Niewiadomska, Teresa Pojmańska. (2011). Multiple techniques of digenean trematodes to finish their life cycles


Klaus Rohde. (2011). The Aspidogastrea: A Parasitological version I.. 


Mailles A., Capek I., Ajana F., Schepens C., Ilef D., Vaillant V., (2006). Commercial watercress as an emerging source of fascioliasis in north France in 2002: results of break out investigation. Epidemiol infect 2006;1-4.

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Seaton D.R. (1979) Cestodes and Trematodes. In: Donaldson R.J. (eds) Parasites and also Western Man. Springer, Dordrecht.