Editing Symbion

{{Short description|Phylum of microscopic organisms that are commensal with lobsters}}
{{About||the term 'symbiont'|Symbiosis|the US power company|Symbion Power}}
{{Distinguish|Symbian|Sybian}}
{{Automatic taxobox
| greatgreatgrandparent_authority = [[Peter Funch|Funch]] & [[Reinhardt Kristensen|Kristensen]], 1995
| greatgrandparent_authority = Funch & Kristensen, 1995
| grandparent_authority = Funch & Kristensen, 1995
| parent_authority = Funch & Kristensen, 1995
| taxon = Symbion
| image = CYC-000075 hab Symbion pandora Paratype.tif
| image_caption = ''Symbion pandora''
| image2 = CYC-000249 hab Symbion americanus Paratype.tif
| image2_caption = ''Symbion americanus''
| authority = Funch & Kristensen, 1995
| display_parents = 5
| subdivision_ranks = Species
| subdivision = 
*''[[Symbion americanus]]'' <small>[[Matthias Obst|Obst]], Funch & Kristensen, 2005</small>
*''[[Symbion pandora]]'' <small>Funch & Kristensen, 1995</small>
*and at least one other
}}

'''''Symbion''''' is a [[genus]] of [[Commensalism|commensal]] aquatic animals, less than 0.5&nbsp;mm wide, found living attached to the mouthparts of cold-water lobsters. They have sac-like bodies, and three distinctly different forms in different parts of their two-stage life-cycle. They appear so different from other animals that they were assigned their own, new [[phylum]] '''Cycliophora''' shortly after they were discovered in 1995.<ref>{{cite web |url=https://www.newscientist.com/article/dn18834-zoologger-the-most-bizarre-life-story-on-earth/ |title=Zoologger: The most bizarre life story on Earth? |last=Marshall |first=Michael |date=28 April 2010 |website=New Scientist |access-date=19 November 2018 |quote=...&nbsp;In 1995, Peter Funch and Reinhardt Møbjerg Kristensen, both then at the University of Copenhagen, Denmark, discovered an animal so unlike any other that a new phylum – Cycliophora – had to be created just for it.&nbsp;...}}</ref> This was the first new [[phylum]] of multicelled organism to be discovered since the [[Loricifera]] in 1983.

== Taxonomy ==
{{See also|List of bilaterial animal orders}}

''Symbion pandora'' was discovered in 1995 by [[Reinhardt Kristensen]] and [[Peter Funch]]<ref name="KF">{{cite journal |author1=P. Funch  |author2=R. M. Kristensen  |name-list-style=amp |year=1995 |title=Cycliophora is a new phylum with affinities to Entoprocta and Ectoprocta |journal=[[Nature (journal)|Nature]] |volume=378 |pages=711–714 |doi=10.1038/378711a0 |issue=6558|bibcode=1995Natur.378..711F |s2cid=4265849 }}</ref> on the mouthparts of the [[Norway lobster]] (''Nephrops norvegicus''). Other, related, species have since been discovered on:
*  the [[American lobster]] (''Homarus americanus'', host to ''[[Symbion americanus]]'')<ref>{{cite journal |author1=M. Obst |author2=P. Funch |author3=G. Giribet |name-list-style=amp |year=2005 |title=Hidden diversity and host specificity in cycliophorans: a phylogeographic analysis along the North Atlantic and Mediterranean Sea |journal=[[Molecular Ecology]] |volume=14 |pages=4427–4440 |doi=10.1111/j.1365-294X.2005.02752.x |pmid=16313603 |issue=14 |s2cid=26920982 }}</ref><ref name="pmid18937332">{{cite journal |vauthors=Neves RC, Kristensen RM, Wanninger A |title=Three-dimensional reconstruction of the musculature of various life cycle stages of the cycliophoran Symbion americanus |journal=J. Morphol. |volume=270 |issue=3 |pages=257–70 |date=March 2009 |pmid=18937332 |doi=10.1002/jmor.10681|s2cid=206090614 }}</ref>
* the [[European lobster]] (''Homarus gammarus'', host to an as yet unnamed species of ''Symbion'')

The [[genus]] is so named because of its [[Commensalism|commensal relationship]] with the lobster (a form of [[symbiosis]]) &ndash; it feeds on the leftovers from the lobster's own meals.<ref>{{cite journal |author1=P. Funch |author2=P. Thor  |author3=M. Obst  |name-list-style=amp |year=2008 |title=Symbiotic relations and feeding biology of ''Symbion pandora'' (Cycliophora) and ''Triticella flava'' (Bryozoa) |journal=[[Vie et Milieu]] |volume=58 |pages=185–188 }}</ref>

They are peculiar microscopic [[animal]]s, with no obvious close relatives, which were therefore given their own [[phylum (biology)|phylum]], called '''Cycliophora'''. The phylogenetic position of ''Symbion'' is still not finally settled. Currently it is placed in the clade Polyzoa along with the phyla [[Ectoprocta]] and [[Entoprocta]], based on genetic analysis.<ref>[https://www.the-scientist.com/news-opinion/phyla-of-tiny-filter-feeders-find-a-new-spot-on-the-tree-of-life-70193 Phyla of Tiny Filter Feeders Find a New Spot on the Tree of Life]</ref>

== Description ==
[[File:Symbion pandora wikipedia (en).jpg|thumb|Diagram]]
''Symbion pandora'' has a [[symmetry (biology)#Bilateral symmetry|bilateral]], sac-like body with no [[body cavity|coelom]]. There are three basic life stages:

* Asexual Feeding Stage &ndash; At this stage, ''S. pandora'' is neither male nor female. It has a length of 347&nbsp;[[micrometre|μm]] and a width of 113&nbsp;μm. On the posterior end of the sac-like body is a stalk with an adhesive disc, which attaches itself to the host. On the anterior end is a ciliated funnel (mouth) and an anus.
* Sexual Stage
** Male &ndash; ''S. pandora'' has a length of 84&nbsp;μm and a width of 42&nbsp;μm during this stage. It has no mouth or anus, which signifies the absence of a [[digestive system]]. It also has two reproductive organs.
** Female &ndash; ''S. pandora'' is the same size as the male in this stage. It does, however, have a digestive system which collapses and reconstitutes itself as a [[larva]].<ref name="KF"/>

== Reproduction ==
''Symbion'' reproduces both [[asexual reproduction|asexually]] and sexually, and has a complex reproduction cycle, a strategy evolved to produce as many offspring as possible that can survive and find a new host when the lobster they live on sheds its shell. The asexual individuals are the largest ones. The sexual individuals do not eat.

During the autumn they make copies of themselves, where a new individual grows inside the parent body, one offspring at the time. The new offspring attach themselves to an available spot on the lobster, begin to feed and eventually start making new copies of themselves. 

In early winter, the asexual animals start producing males. When a male is born, it crawls away from its parent and glues itself to another asexual individual. Once attached, the male produces two dwarf males inside its body, which turns into a hollow pouch. Each of the two dwarf males are about one hundred times smaller than the asexual individual to which they are attached. Their bodies start out with about 200 cells, but this number has been reduced to just 47 by the time they reach maturity. Thirty-four of the cells form its nervous system, and three more become sensory cells used to help them feel their surroundings. Eight cells becomes mucous glands, which produce mucus that helps them move across the surface. The final two cells form the testes, which make the sperm that fertilize the female's egg. Most of the cells of the dwarf males also lose their nucleus and shrink to almost half their size, which is an adaptation that allows two mature individuals to fit inside the body of the parent male. Two males increases their chances to fertilize a female. 

By late winter, when the large feeding individuals in the colony have males attached to their bodies, they start making females. Each female has a single egg inside her. When she is about to be born, one of the two dwarf males fertilizes her when she comes out. The fertilized female finds herself a place on the host's whiskers where she attaches herself. Inside her the developing embryo extracts all the nutrients it needs to grow from its mother, and by the time it is ready to be born, all that remains of the mother is an empty husk. This new offspring is a strong swimmer unlike all the other forms in the colony, and those who succeed in finding a new host will attach themselves to its mouthparts, where it will grow a stomach and mouthparts, morphing into a large, feeding and asexual type, starting the cycle all over again.<ref>[https://www.sciencenewsforstudents.org/article/living-mysteries-complex-beast-lurks-lobster-whiskers Living Mysteries: This complex beast lurks on lobster whiskers]</ref>
The larval stage may be unscientifically referred to as sea worms.<ref>[[Ross Piper|Piper, Ross]] (2007), ''Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals'', [[Greenwood Press (publisher)|Greenwood Press]].</ref>

== References ==
{{Reflist}}

{{Animalia}}
{{Life on Earth}}
{{Taxonbar|from1=Q502012|from2=Q2783567|from3=Q14427009|from4=Q14426976|from5=Q276292}}

[[Category:Platyzoa genera]]
[[Category:Parasites of crustaceans]]