Editing Polyp (zoology)

{{short description|One of two forms found in the phylum Cnidaria (zoology)}}
{{about|the small aquatic animal|the medical condition|Polyp (medicine)}}
[[File:Polypen einer Gorgonie.jpg|thumb|upright=1.1|[[Gorgonian]] polyps in a reef aquarium]]

A '''polyp''' in [[zoology]] is one of two forms  found in the [[phylum]] [[Cnidaria]], the other being the [[medusa (biology)|medusa]]. Polyps are roughly [[cylindrical]] in shape and elongated at the axis of the [[vase]]-shaped body. In solitary polyps, the [[aboral]] (opposite to oral) end is attached to the [[substrate (biology)|substrate]] by means of a disc-like [[holdfast (biology)|holdfast]] called a [[pedal disc]], while in [[colony (biology)|colonies]] of polyps it is connected to other polyps, either directly or indirectly. The oral end contains the [[mouth]], and is surrounded by a circlet of [[tentacle]]s.

==Classes==
In the class [[Anthozoa]], comprising the [[sea anemones]] and [[coral]]s, the individual is always a polyp; in the class [[Hydrozoa]], however, the individual may be either a polyp or a [[medusa (biology)|medusa]],<ref name=EB1911>{{EB1911 |wstitle=Polyp |volume=22 |page=37 |first=Edward Alfred |last=Minchin |inline=1}}</ref> with most species undergoing a [[biological life cycle|life cycle]] with both a polyp stage and a medusa stage.

In the class [[Scyphozoa]], the medusa stage is dominant, and the polyp stage may or may not be present, depending on the [[family (biology)|family]]. In those scyphozoans that have the [[larval]] planula [[metamorphose]] into a polyp, the polyp, also called a "[[scyphistoma]]," grows until it develops a stack of plate-like medusae that pinch off and swim away in a process known as [[strobilation]]. Once strobilation is complete, the polyp may die, or [[regeneration (biology)|regenerate]] itself to repeat the process again later. With [[cubozoa]]ns, the [[planula]] settles onto a suitable surface, and develops into a polyp.  The cubozoan polyp then eventually metamorphoses directly into a medusa.{{Citation needed|date=January 2025}}

==Anatomy==
[[Image:Coral polyp.jpg|thumb|Anatomy of a [[coral]] polyp]]{{One source|date=January 2025|section}}
The body of the polyp may be roughly compared in a structure to a sac, the wall of which is composed of two layers of [[cell (biology)|cell]]s. The outer [[Germ layer|layer]] is known technically as the ''[[ectoderm]]'', with the inner layer as the ''[[endoderm]]'' (or ''gastroderm''). Between ectoderm and endoderm is a supporting layer of structureless gelatinous substance termed [[mesogloea|mesoglea]], secreted by the cell layers of the body wall.<ref name="EB1911" /> The mesoglea can be thinner than the endoderm or ectoderm or comprise the bulk of the body as in larger [[jellyfish]]. The mesoglea can contain [[endoskeleton|skeletal]] elements derived from cells [[cell migration|migrated]] from ectoderm.{{Citation needed|date=January 2025}}

The sac-like body built up in this way is attached usually to some firm object by its blind end, and bears at the upper end the mouth which is surrounded by a circle of [[tentacle]]s which resemble glove fingers. The tentacles are [[organ (anatomy)|organ]]s which serve both for the [[tactile sense]] and for the capture of food.<ref name="EB1911" /> Polyps extend their tentacles, particularly at night, containing coiled stinging nettle-like cells, or [[nematocyst]]s, which pierce, poison, and firmly hold living prey paralysing or killing them. Polyp prey includes [[copepods]] and fish [[larva]]e.<ref>Chang, T.D. and Sullivan, J.M. "[http://www.dartmouth.edu/~biofsp/pdf08/133_SIFP1_ACCEPTED_coral_zoops.pdf Temporal associations of coral and zooplankton activity on a Caribbean reef] {{webarchive|url=https://web.archive.org/web/20110606021125/http://www.dartmouth.edu/~biofsp/pdf08/133_SIFP1_ACCEPTED_coral_zoops.pdf |date=2011-06-06 }}" Dartmouth Studies in Tropical Ecology. 2008. Accessed 2009-06-21.</ref> Longitudinal [[muscular fibril]]s formed from the cells of the ectoderm allow tentacles to contract when conveying the food to the mouth. Similarly, circularly disposed muscular fibrils formed from the endoderm permit tentacles to be protract or thrust out once they are contracted. These muscle fibres belong to the same two systems, allowing the whole body to retract or protrude outwards.<ref name="EB1911" />

We can distinguish therefore in the body of a polyp the column, circular or oval in section, forming the trunk, resting on a base or foot and surmounted by the crown of tentacles, which enclose an area termed the [[peristome]], in the centre of which again is the mouth. Generally, there is no other opening to the body except the mouth, but in some cases [[excretory]] pores are known to occur in the foot, and pores may occur at the tips of the tentacles. A polyp is an animal of very simple structure,<ref name="EB1911" /> a [[living fossil]] that has not changed significantly for about half a billion years (per generally accepted dating of [[Cambrian]] [[sedimentary rock]]).{{Citation needed|date=January 2025}}

The external form of the polyp varies greatly in different cases. The column may be long and slender, or may be so short in the vertical direction that the body becomes disk-like. The tentacles may number many hundreds or may be very few, in rare cases only one or two. They may be long and filamentous, or short and reduced to mere knobs or warts. They may be simple and unbranched, or they may be feathery in pattern. The mouth may be level with the surface of the peristome, or may be projecting and trumpet-shaped. As regards internal structure, polyps exhibit two well-marked types of organization, each characteristic of one of the two classes, Hydrozoa and Anthozoa.<ref name=EB1911/>

In the class Hydrozoa, the polyps are indeed often very simple, like the common little [[fresh water]] species of the genus ''[[Hydra (genus)|Hydra]]''. Anthozoan polyps, including the corals and sea anemones, are much more complex due to the development of a tubular [[stomodaeum]] leading inward from the mouth and a series of radial partitions called [[Mesentery (zoology)|mesenteries]]. Many of the mesenteries project into the enteric cavity but some extend from the body wall to the central stomodaeum.{{Citation needed|date=January 2025}}

==Reproduction==
It is an almost universal attribute of polyps to reproduce [[asexual reproduction|asexually]] by the method of [[budding]]. This mode of [[reproduction]] may be combined with [[sexual reproduction]], or may be the sole method by which the polyp produces [[offspring]], in which case the polyp is entirely without [[sexual organ]]s.<ref name=EB1911/>

===Asexual reproduction===
In many cases the buds formed do not separate from the parent but remain in continuity with it, thus forming [[Colony (biology)|colonies]] or stocks, which may reach a great size and contain a vast number of individuals. Slight differences in the method of budding produce great variations in the form of the colonies. The [[reef]]-building [[coral]]s are polyp-colonies, strengthened by the formation of a firm skeleton.<ref name=EB1911/>

===Sexual reproduction===
Among sea anemones, [[sexual plasticity]] may occur.  That is, asexually produced clones derived from a single founder individual can contain both male and female individuals ([[ramets]]).<ref name="pmid20686700">{{cite journal |vauthors=Schlesinger A, Kramarsky-Winter E, Rosenfeld H, Armoza-Zvoloni R, Loya Y |title=Sexual plasticity and self-fertilization in the sea anemone Aiptasia diaphana |journal=PLOS ONE |volume=5 |issue=7 |pages=e11874 |year=2010 |pmid=20686700 |pmc=2912375 |doi=10.1371/journal.pone.0011874 |bibcode=2010PLoSO...511874S |doi-access=free }}</ref> When eggs and sperm (gametes) are formed, they can produce [[zygotes]] derived from "selfing" (within the founding clone) or out-crossing, that then develop into swimming planula larvae.{{Citation needed|date=January 2025}}

[[File:Polyps of Cnidaria colony.jpg|thumb|Polyps of a colony of [[Cnidaria]]]]

The overwhelming majority of stony coral (''[[Scleractinia]]'') taxa are [[Hermaphrodite|hermaphroditic]] in their adult colonies.<ref name=Heyward>Heyward AJ, Babcock, RC (1986).  Self- and cross-fertilization in scleractinian corals.  Marine Biology 90, 191–195</ref> In these species, there is ordinarily synchronized release of [[egg]]s and [[sperm]] into the water during brief spawning events.<ref name="pmid17742935">{{cite journal |vauthors=Harrison PL, Babcock RC, Bull GD, Oliver JK, Wallace CC, Willis BL |title=Mass spawning in tropical reef corals |journal=Science |volume=223 |issue=4641 |pages=1186–9 | date=March 1984 |pmid=17742935 |doi=10.1126/science.223.4641.1186 |bibcode=1984Sci...223.1186H |s2cid=31244527 }}</ref> Although some species are capable of [[self-fertilization]] to varying extents, [[cross-fertilization]] appears to be the dominant mating pattern.<ref name=Heyward />

==Etymology==
The name polyp was given by [[René Antoine Ferchault de Réaumur]]<ref>Stott, Rebecca. "Darwin's ghosts: the secret history of evolution" New York, Spiegel & Grau (2012). {{ISBN|9781400069378}}</ref> to these organisms from their superficial resemblance to an [[octopus]] ({{langx|fr|poulpe}}, ultimately from Ancient Greek adverb {{lang|grc|πολύ}} ({{Transliteration|grc|poly}}, "much") + noun {{lang|grc|πούς}} ({{Transliteration|grc|pous}}, "foot")), with its circle of writhing arms round the mouth. This comparison contrasts to the common name "coral-insects", applied to the polyps which form [[coral]].<ref name=EB1911/>

== Threats ==
75% of the world's corals are threatened<ref>{{Cite web|title = NOAA's Coral Reef Conservation Program: New Analysis: 75% of Coral Reefs Under Threat|url = http://coralreef.noaa.gov/aboutcrcp/news/featuredstories/feb11/cu_threat/|website = coralreef.noaa.gov|access-date = 2015-06-08}}</ref> due to [[overfishing]], destructive fishing, coastal development, [[pollution]], thermal stress, [[ocean acidification]], [[crown-of-thorns starfish]], and introduced [[invasive species]].<ref>{{Cite document|title = Reefs at Risk Revisited|last = Burke|first = Reytar|date = 2011|publisher= World Resources Institute}}</ref>

In recent decades the conditions that corals and polyps have found themselves in have been changing, leading to new diseases being observed in corals in many parts of the world, posing even greater risk to an already pressured animal.<ref>{{Cite journal|last=Barrero-Canosa-1, Duenas-2, Sanchez-3|first=J.-1, L.F.-2, J.A.-3|date=March 2013|title=Isolation of potential fungal pathogens in gorgonian corals at the Tropical Eastern Pacific|journal=Coral Reefs; Heidelberg|volume=32|issue=1|pages=35–41|doi=10.1007/s00338-012-0972-2|bibcode=2013CorRe..32...35B|s2cid=17561903|id={{ProQuest|1357199805}}}}</ref> [[Aquatic life]] has been put under a substantial amount of stress because of the pollutants caused by land-based [[agriculture]]. Particularly, exposure to the insecticide [[profenofos]] and the fungicide MEMC have played a major part in polyp retraction and biomass decrease.<ref>{{Cite journal|url=https://researchonline.jcu.edu.au/2611/1/2611_Markey_et_al...2007.pdf |archive-url=https://ghostarchive.org/archive/20221009/https://researchonline.jcu.edu.au/2611/1/2611_Markey_et_al...2007.pdf |archive-date=2022-10-09 |url-status=live|title=Insecticides and a fungicide affect multiple coral life stages|journal=Marine Ecology Progress Series|volume=330|pages=127–137|last=Markey, Kathryn L., Baird, Andrew H., Humphrey, Craig, and Negri, Andrew P|date=2007|bibcode=2007MEPS..330..127M|doi=10.3354/meps330127|doi-access=free}}</ref><ref>{{Cite journal|title=Differential gene expression in juvenile polyps of the coral Acropora tenuis exposed to thermal and chemical stresses|journal=Journal of Experimental Marine Biology and Ecology|volume=430-431|pages=17–24|doi=10.1016/j.jembe.2012.06.020|year=2012|last1=Yuyama|first1=Ikuko|last2=Ito|first2=Yoshihiko|last3=Watanabe|first3=Toshiki|last4=Hidaka|first4=Michio|last5=Suzuki|first5=Yoshimi|last6=Nishida|first6=Mutsumi|bibcode=2012JEMBE.430...17Y }}</ref>

There have been many experiments supporting the hypothesis that heat stress in ''[[Acropora tenuis]]'' juvenile polyps provokes an up-regulation of protein in the [[endoplasmic reticulum]]. The results vary based on the polyp characteristics such as age, type, and growth stage.{{Citation needed|date=January 2025}}

==See also==
*[[Portuguese man o' war]]
*[[Zoanthid]]

==Notes==
{{Reflist}}

==External links==
{{commons|Polyp (zoology)}}
* {{cite web|url=http://etic.univ-reunion.fr/hydroids/|archive-url=https://web.archive.org/web/20061208023823/http://etic.univ-reunion.fr/hydroids/|url-status=dead|archive-date=8 December 2006|title=Hydroids from Reunion Island and the Indian Ocean|date=8 December 2006|access-date=5 June 2019}}<
* {{cite web|url=http://ocean.si.edu/ocean-life/invertebrates/corals-and-coral-reefs|title=Corals and Coral Reefs|website=Smithsonian Ocean|access-date=5 June 2019}}
* {{cite web|url=https://www.coris.noaa.gov/about/what_are/|title=NOAA's Coral Reef Information System (CoRIS) - What are Coral Reefs|first=National Oceanic and Atmospheric Administration|last=US Department of Commerce|website=www.coris.noaa.gov|access-date=5 June 2019}}
* {{cite web|url=https://coral.org/coral-reefs-101/coral-reef-ecology/coral-polyps/|title=Coral Polyps - Coral Reef Alliance|website=coral.org|access-date=5 June 2019}}
* {{cite web|url=https://www.icriforum.org/about-coral-reefs/what-are-corals|title=What are corals? - International Coral Reef Initiative|website=www.icriforum.org|access-date=5 June 2019}}

[[Category:Cnidarian biology]]