Editing Monogenea

{{Short description|Class of ectoparasitic flatworms}}
{{More citations needed|date=March 2007}}
{{Automatic taxobox
| image = Echinoplectanum laeve body.jpg
| image_caption = ''Echinoplectanum laeve''
| taxon = Monogenea
| authority = Carus, 1863
| subdivision_ranks = Subgroups
| subdivision = [[#Systematics and evolution|See text]].
}}

'''Monogeneans''', members of the class '''Monogenea''', are a group of ectoparasitic [[flatworm]]s commonly found on the skin, [[gills]], or fins of fish. They have a direct lifecycle and do not require an intermediate host. Adults are hermaphrodites, meaning they have both male and female reproductive structures.<ref name="tub" >L.A. Tubbsa et al. (2005). "Effects of temperature on fecundity in vitro, egg hatching and reproductive development of ''Benedenia seriolae'' and ''Zeuxapta seriolae'' (Monogenea) parasitic on yellowtail kingfish Seriola lalandi". ''International Journal for Parasitology''(35), 315–327.</ref>

Some monogeneans are [[oviparous]] (egg-laying) and some are [[viviparous]] (live-bearing). Oviparous varieties release eggs into the water. Viviparous varieties release larvae, which immediately attach to another host. The genus ''Gyrodactylus''  is an example of a viviparous variety, while the genus ''Dactylogyrus'' is an example of an oviparous variety.<ref name="tub" />

== Signs and symptoms ==
[[File:Dobbeltdyr.gif|220px|thumb|''[[Diplozoon paradoxum]]'']]
Freshwater fish that become infected with this parasite become lethargic and end up swimming towards the surface of the water. In addition, some may be seen rubbing the bottom or sides of their skin where the parasite is located. Infected skin where the parasite is attached may show areas of scale loss and may produce a pinkish fluid. Gills that are infected  may appear swollen and pale. "Pipping", which is gulping for air at the water surface, could indicate severe respiratory distress.<ref name="reed" >Reed, Peggy et al. Monogenean Parasites of Fish. ''Institute of Food and Agricultural Sciences''.  . http://www.aces.edu/dept/fisheries/education/ras/publications/Update/Monogenean%20Parasites%20of%20Fish.pdf
</ref>

In salt water fish, Monogeneans can infect the skin and gills, resulting in irritations to the host. Heavy infections could result in erratic swimming behavior. Affected gills may become irritated and swollen.<ref name="reed" />

==Characteristics==
Monogenea are small parasitic flatworms mainly found on skin or gills of fish.
They are rarely longer than about 2&nbsp;cm. A few species infecting certain marine fish are larger, and marine forms are generally larger than those found on freshwater hosts. Monogenea are often capable of dramatically elongating and shortening as they move. Biologists need to ensure that specimens are completely relaxed before measurements are taken.<ref name=":0">Roberts, S. Larry & John Janovy, Jr. ''Foundations of Parasitology''</ref>

Monogeneans lack respiratory, skeletal, and circulatory systems but they do have posterior attachment structures in the form of adhesives, clamps, hamuli and suckers.<ref name=":0" /><ref>[http://www.britannica.com/EBchecked/topic/209735/flatworm/64463/Annotated-classification#ref=ref529438 flatworm :: Annotated classification - Britannica Online Encyclopedia<!-- Bot generated title -->]</ref> Like other flatworms, Monogenea have no true [[body cavity]] (coelom). They have a simple digestive system consisting of a mouth opening with a muscular [[pharynx]] and an intestine with no terminal opening ([[anus]]).

Monogenea are Platyhelminthes, so are among the lowest invertebrates to possess three embryonic germ layers—[[endoderm]], [[mesoderm]], and [[ectoderm]]. In addition, they have a head region that contains concentrated sense organs and nervous tissue (brain).

Like all ectoparasites, monogeneans have well-developed attachment structures. The anterior structures are collectively termed the '''prohaptor''', while the posterior ones are collectively termed the '''opisthaptor''', or simply [[haptor]]. The posterior opisthaptor with its hooks, anchors, clamps etc. is typically the major attachment organ.

Generally, monogeneans also are [[hermaphroditic]] with functional reproductive organs of both sexes occurring in one individual. Most species are oviparous, but a few are viviparous.

==Phylogeny==
The following cladogram depicts the [[phylogeny|phylogenetic]] relationships of the different monogenean orders:<ref>{{citation|journal=International Journal for Parasitology|date=March 2002|pages=233–244|volume=32|issue=3|title=Phylogenetics of the Monogenea – evidence from a medley of molecules|vauthors=Olson PD, ((Littlewood DTJ))|doi=10.1016/S0020-7519(01)00328-9|pmid=11835967 |url=http://olsonlab.com/resources/Publications/Olson.IJP.2002.pdf|access-date=May 19, 2022}}</ref><ref>{{cite book|first1=Walter A.|last1=Boeger|first2=Delane C.|last2=Kritsky|chapter=Phylogenetic relationships of the Monogenoidea|editor-first1=D.T.J.|editor-last1=Littlewood|editor-first2=R.A.|editor-last2=Bray|title=Interrelationships of the Platyhelminthes|date=2001|publisher=CRC Press|isbn=9780367397852|edition=1st}}</ref>
{{clade|label1='''Monogenea'''
|1={{clade|label1=[[Monopisthocotylea]]|sublabel1=Polyonchoinea|1={{clade|1=[[Monocotylidea]]|2={{clade|1=[[Capsalidea]]|2={{clade|1={{clade|1=[[Lagarocotylidea]]|2=[[Montchadskyellidea]]}}|2={{clade|1=[[Gyrodactylidea]]|2=[[Dactylogyridea]]}}}}}}}}|label2=[[Polyopisthocotylea]]|sublabel2=Heteronchoinea|2={{clade|1=[[Polystomatidea]]|label2=Oligonchoinea|2={{clade|1=[[Chimaericolidea]]|2={{clade|1=[[Diclybothriidea]]|2=[[Mazocraeidea]]}}}}}}}}}}

==Systematics and evolution==
The ancestors of Monogenea were probably free-living flatworms similar to modern [[Turbellaria]].
According to the more widely accepted view, "rhabdocoel turbellarians gave rise to monogeneans; these, in turn, gave rise to [[digeneans]], from which the [[cestodes]] were derived. Another view is that the rhabdocoel ancestor gave rise to two lines; one gave rise to monogeneans, which gave rise to digeneans, and the other line gave rise to cestodes".<ref name="tub" />

About 50 [[family (biology)|families]] and thousands of species are described{{citation needed|date=May 2022}}.

Some parasitologists divide the Monogenea into two (or three) subclasses based on the complexity of their haptor: the [[Monopisthocotylea]] have one main part to the haptor, often with hooks or a large attachment disc, whereas the [[Polyopisthocotylea]] have multiple parts to the haptor, typically clamps.  These groups are also known as Polyonchoinea and Heteronchoinea, respectively.  Polyopisthocotyleans are almost exclusively gill-dwelling blood feeders, whereas monopisthocotyleans may live on the gills, skin, and fins.

[[Monopisthocotylea]] include:
*Genus ''[[Gyrodactylus]]'' has no eyespots and is viviparous.
*Genus ''[[Dactylogyrus]]'' has four [[eyespot (flatworm)|eyespot]]s and is oviparous.  This is one of the largest metazoan genera, with at least 970 species.
*Genus ''[[Neobenedenia]]'' much larger and lives on the skin of many tropical marine species, causing problematic infections in marine aquaria.
All of these can cause [[epizootic]]s in [[freshwater fish]] when raised in [[aquaculture]].

[[Polyopisthocotylea]] include:
*Genus ''[[Diclidophora]]'' is primarily found in [[marine fish]] and primitive freshwater fish such as [[sturgeon]]s and [[paddlefish]].
*Genus ''[[Protopolystoma]]'' is found in aquatic clawed toads (''[[Xenopus]]'' species).

==Ecology and lifecycle==
[[File:Parasite130103-fig1 Protopolystoma xenopodis (Monogenea, Polystomatidae) egg.tif|thumb|left|Eggs of the monogenean ''[[Protopolystoma xenopodis]]'',<ref>Theunissen, M., Tiedt, L. & Du Preez, L. H. 2014: The morphology and attachment of ''Protopolystoma xenopodis'' (Monogenea: Polystomatidae) infecting the African clawed frog ''Xenopus laevis''. Parasite, 21, 20. {{doi|10.1051/parasite/2014020}}</ref> a parasite of the African clawed frog ''[[Xenopus laevis]]]]
Monogeneans possess the simplest lifecycle among the parasitic platyhelminths.  They have no intermediate hosts and are ectoparasitic on fish (seldom in the [[urinary bladder]] and [[rectum]] of [[Poikilotherm|cold-blooded]] [[vertebrates]]).  Although they are [[hermaphrodite]]s, the male reproductive system becomes functional before the female part. The eggs hatch releasing a heavily ciliated larval stage known as an [[oncomiracidium]].  The oncomiracidium has numerous posterior hooks and is generally the life stage responsible for transmission from host to host.<br />
No known monogeneans infect [[birds]], but one (''[[Oculotrema hippopotami]]'') infects [[mammals]], parasitizing the eye of the [[hippopotamus]].

==See also==
{{Annotated link|Gastrocotylinae}}

== References ==
{{Reflist}}

== External links ==
* [http://clinicalsciences.wordpress.com/article/monogenea-ectoparasitic-flukes-flatworms-xk923bc3gp4-75/ Monogenea – ectoparasitic flukes (flatworms)] - Clinical Sciences

{{Fish disease topics}}
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[[Category:Monogenea| ]]
[[Category:Protostome classes]]