View source for Tentacle

{{Short description|Varied organ found in many animals and used for palpation and manipulation}}
{{About|tentacles in zoology}}
{{Use dmy dates|date=March 2017}}
[[Image:cuttlefish.png|thumb|upright|[[Cuttlefish]] with two tentacles and eight arms]]
In [[zoology]], a '''tentacle''' is a flexible, mobile, and elongated [[organ (anatomy)|organ]] present in some species of [[animal]]s, most of them [[invertebrate]]s. In animal anatomy, tentacles usually occur in one or more pairs. Anatomically, the tentacles of animals work mainly like [[muscular hydrostat]]s. Most forms of tentacles are used for grasping and feeding. Many are [[Sensory system|sensory organs]], variously receptive to [[somatosensory system|touch]], [[visual perception|vision]], or to the [[Chemoreceptor|smell or taste]] of particular foods or threats. Examples of such tentacles are the [[eyestalk]]s of various kinds of [[snail]]s. Some kinds of tentacles have both sensory and manipulatory functions.
A tentacle is similar to a [[cirrus (biology)|cirrus]], but a cirrus is an organ that usually lacks the tentacle's strength, size, flexibility, or sensitivity.  A [[nautilus]] has cirri, but a [[squid]] has tentacles.
==Invertebrates==
=== Molluscs ===
{{See also|Cephalopod limb}}
[[Image:Snail-front-0A.jpg|thumb|right|Front view of land snail showing upper and lower sets of tentacles]]
[[Image:White abalone Haliotis sorenseni.jpg|thumb|350 px|Abalone showing pallial tentacles]]
Many molluscs have tentacles of one form or another. The most familiar are those of the [[Pulmonata|pulmonate land snails]], which usually have two sets of tentacles on the head: when extended the upper pair have eyes at their tips; the lower pair are [[chemoreceptor]]s. Both pairs are fully retractable [[muscular hydrostat]]s, but they are not used for manipulation or prey capture. Molluscs have one pair of tentacles close to their mouths that hold close to their captured prey before they can consume it.<ref name="FiCaDB">{{cite journal |last1=Kier |first1=William M. |date=February 2016 |title=The Musculature of Coleoid Cephalopod Arms and Tentacles |journal=Frontiers in Cell and Developmental Biology |volume=4 |page=10 |doi=10.3389/fcell.2016.00010|doi-access=free |pmid=26925401 |pmc=4757648 }}</ref>
Some marine snails such as [[abalone]] and top snails, [[Trochidae]], have numerous small tentacles around the edge of the [[mantle (mollusc)|mantle]]. These are known as ''pallial tentacles''.<ref name=bou/>
Among [[cephalopod]]s, squid have spectacular tentacles. They take the form of highly mobile muscular hydrostats with various appendages such as suction disks and sometimes thorny hooks. Up to the early twentieth century "tentacles" were interchangeably called "arms".<ref name= "CNH3">{{cite book |last1=Cooke |first1= A. H.  |last2=Shipley |first2=Arthur Everett  |date=1895 |title=The Cambridge Natural History |volume=34: Molluscs, Trilobites, Brachiopods etc. |location=London, England, U.K. |publisher= Macmillan Company}}{{page needed|date=October 2023}}</ref> These tentacles are made of stalks of axial [[ventral nerve cord|nerve cord]]s that are covered by circular transverse muscle tissue that contract in response to stimuli. There is a layer of helical muscle that helps each tentacle to twist or turn in any direction where the prey is sensed.<ref name="FiCaDB"/>
The modern convention, however, is to speak of appendages as "tentacles" when they have relatively thin "[[peduncle (anatomy)|peduncles]]" or "stalks" with "clubs" at their tips. In contrast the convention refers to the relatively shorter appendages as "arms". By this definition the eight appendages of octopuses, though quite long, count as arms.<ref name=bou>{{cite web |author= Boumis R |title= Animals With Tentacles |url= http://animals.pawnation.com/animals-tentacles-2495.html |year= 2013 |work= Pawnation |publisher= AOL Inc. |access-date= 2013-06-08 |url-status= live |archive-url= https://web.archive.org/web/20131203020936/http://animals.pawnation.com/animals-tentacles-2495.html |archive-date= 3 December 2013 |df= dmy-all }}</ref> While arms are distinct from tentacles (a definition specific to the limb featuring peduncles), arms do fall within the general definition of "tentacle" as "a flexible, mobile, and elongated organ" and "tentacle" could be used as an [[umbrella term]].
The tentacles of the [[giant squid]] and [[colossal squid]] have powerful suckers and pointed teeth at the ends. The teeth of the giant squid resemble [[crown cork|bottle caps]] and function like tiny [[hole saw]]s, while the tentacles of the colossal squid wield two long rows of swiveling, tri-pointed hooks.
===Cnidarians===
[[Cnidarian]]s, such as [[jellyfish]], [[sea anemone]]s, ''[[Hydra (genus)|Hydra]]'' and [[coral]] have numerous hair-like tentacles. Cnidarians have huge numbers of [[cnidocyte]]s on their tentacles. In [[jellyfish|medusoid form]], the body floats on water so that the tentacles hang down in a ring around the mouth. In [[polyp (zoology)|polyp]] form, such as sea anemone and coral, the body is below with the tentacles pointed upwards.
The tentacles of the [[lion's mane jellyfish]] may be up to {{convert|37|m|ft|abbr=on}} long. They are hollow and are arranged in 8 groups of between 70 and 150. The longer tentacles are equipped with cnidocytes whose venom paralyses and kills prey. The smaller tentacles guide food into the mouth.<ref>{{cite web | author= Kosner AW | title= Lion's Mane Jellyfish Image: This Is (Literally) How Things Blow Up On The Internet! | url= https://www.forbes.com/sites/anthonykosner/2012/07/10/lions-mane-jellyfish-image-this-is-literally-how-things-blow-up-on-the-internet/2/ | date= 10 July 2012 | work=[[Forbes]] | access-date= 2013-06-08 | url-status= live | archive-url= https://web.archive.org/web/20130625154715/http://www.forbes.com/sites/anthonykosner/2012/07/10/lions-mane-jellyfish-image-this-is-literally-how-things-blow-up-on-the-internet/2/ | archive-date= 25 June 2013 | df= dmy-all }}</ref><ref>{{cite web|author=Wild Facts|title=Wild Fact #419 – One Large Jelly – Lion's Mane Jellyfish|url=http://www.wild-facts.com/2011/wild-fact-419-one-large-jelly-lions-mane-jellyfish/|date=29 November 2011|work=wild-facts.com|access-date=2013-06-08|url-status=live|archive-url=https://web.archive.org/web/20121219091103/http://www.wild-facts.com/2011/wild-fact-419-one-large-jelly-lions-mane-jellyfish/|archive-date=19 December 2012|df=dmy-all}}</ref>
===Ctenophores===
Many species of the jellyfish-like [[ctenophore]]s have two tentacles, while some have none. Their tentacles have adhesive structures called ''[[colloblast]]s'' or ''lasso cells''. The colloblasts burst open when prey comes in contact with the tentacle, releasing sticky threads that secure the food.<ref>{{cite web | author= Bird J | title= CNIDARIANS: SIMPLE ANIMALS WITH A STING! | url= http://www.oceanicresearch.org/education/wonders/cnidarian.html | date= 5 June 2007 | work= oceanicresearch.org | publisher= Oceanic Research Group | access-date= 2013-06-08 | url-status= live | archive-url= https://web.archive.org/web/20130707024559/http://www.oceanicresearch.org/education/wonders/cnidarian.html | archive-date= 7 July 2013 | df= dmy-all }}</ref>
===Bryozoa===
[[Bryozoa]] (moss animals) are tiny creatures with tentacles around their mouths. The tentacles are almost cylindrical and have bands of cilia which create a water current towards the mouth. The animal extracts edible material from the flow of water.<ref>{{Cite book | author= Claus N | title= Bryozoa (Ectoprocta: 'Moss' Animals) | url= http://www.els.net/WileyCDA/ElsArticle/refId-a0001613.html | date= May 2013 | work= els.net | publisher= eLS. John Wiley & Sons Ltd | doi= 10.1002/9780470015902.a0001613.pub2 | access-date= 2013-06-08 | url-status= live | archive-url= https://web.archive.org/web/20130605003827/http://www.els.net/WileyCDA/ElsArticle/refId-a0001613.html | archive-date= 5 June 2013 | df= dmy-all | isbn= 978-0470016176 }}</ref>
===Trypanorhynch cestodes===
{{multiple image
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| image1    = Parasite140092-fig3 - FIG11 Nybelinia basimegacantha body.png
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| caption1  = A larva of [[trypanorhynch]] cestode (only two tentacles shown). Scale-bar: 0.1 mm
| image2    = FIG11 Nybelinia basimegacantha Tentacle.png
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| caption2  = Detail of one tentacle with its spines. Scale-bar: 0.01 mm.
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[[Trypanorhynch]] [[cestode]]s are parasitic in fish. Their [[scolex]] shows four tentacles which are covered by spines. These tentacles help the adult cestode to attach to the intestine of the shark or ray that they parasitize. The same tentacles are also present in the larvae.<ref name="BeveridgeBray2014">{{cite journal|last1=Beveridge|first1=Ian|last2=Bray|first2=Rodney A.|last3=Cribb|first3=Thomas H.|last4=Justine|first4=Jean-Lou|title=Diversity of trypanorhynch metacestodes in teleost fishes from coral reefs off eastern Australia and New Caledonia|journal=Parasite|volume=21|year=2014|pages=60|issn=1776-1042|doi=10.1051/parasite/2014060|pmid=25402635|pmc=4234045|url=https://www.parasite-journal.org/articles/parasite/full_html/2014/01/parasite140092/parasite140092.html|url-status=live|archive-url=https://web.archive.org/web/20180109144048/https://www.parasite-journal.org/articles/parasite/full_html/2014/01/parasite140092/parasite140092.html|archive-date=9 January 2018|df=dmy-all}} {{open access}}</ref>
==Vertebrates==
===Amphibians===
The legless [[amphibian]]s called [[caecilian]]s have two short tentacles, one on each side of the head, between their eyes and nostrils. The current opinion is that these tentacles supplement the normal sense of smell, possibly for navigation and to locate prey underground.<ref name=bou/>
===Mammals===
The [[star-nosed mole]], ''Condylura cristata'', of [[North America]], has 22 short but conspicuous tentacles around its nose. They are mobile and extremely sensitive, helping the animal to find its way about the burrow and detect prey. They are about 1–4&nbsp;mm long and hold about 25,000 [[Somatosensory system|touch receptors]] called [[Eimer's organ]]s, perhaps giving this mole the most delicate sense of touch among mammals.<ref name=bou/>
{{anchor|tentilla}}
==Tentillum==
[[File:Ctenophore.jpg|thumb|Deep-sea ctenophore trailing tentacles studded with tentilla]]
The word '''tentillum''' ({{plural form}}: '''tentilla''') literally means "little tentacle". However, irrespective of size, it usually refers to a side branch of a larger tentacle. In some cases, such tentilla are specialised for particular functions; for example, in the [[Cnidaria]] tentilla usually bear [[cnidocyte]]s,<ref>[http://species-identification.org/species.php?species_group=zsao&selected=definitie&menuentry=woordenlijst&record=tentilla Marine Species Identification Portal : Zooplankton of the South Atlantic Ocean : Glossary : tentilla] {{webarchive|url=https://web.archive.org/web/20131202231841/http://species-identification.org/species.php?species_group=zsao&selected=definitie&menuentry=woordenlijst&record=tentilla |date=2 December 2013 }}. Species-identification.org. Retrieved on 2013-05-02.</ref> whereas in the [[Ctenophora]] they usually have [[collocyte]]s.<ref name="CNH1">Harmer, Sir Sidney Frederic; Shipley, Arthur Everett et al. (1906) ''The Cambridge Natural History Volume 1, Protozoa, Porifera, Coelenterata, Ctenophora, Echinodermata''. Macmillan Company.</ref><ref>{{cite journal|author1=Mackie G.O.|author2=Mills C.E.|author3=Singla C.L.|title=Structure and function of the prehensile tentilla of ''Euplokamis'' (Ctenophora, Cydippida)|doi=10.1007/BF00312216|url=http://faculty.washington.edu/cemills/EuplokamisTentacle1988.pdf|year=1988|journal=Zoomorphology|volume=107|issue=6|pages=319|s2cid=317017|url-status=live|archive-url=https://web.archive.org/web/20160303233312/http://faculty.washington.edu/cemills/EuplokamisTentacle1988.pdf|archive-date=3 March 2016|df=dmy-all}}</ref> [[Siphonophorae|Siphonophores]] are an example of Cnidaria that use tentilla.
==References==
{{Reflist}}
==External links==
{{Commons category|Tentacles}}
*[http://animals.about.com/od/t/g/tentacle.htm Tentacle] {{Webarchive|url=https://web.archive.org/web/20130514203145/http://animals.about.com/od/t/g/tentacle.htm |date=14 May 2013 }} at [[About.com]]
*[http://www.britannica.com/EBchecked/topic/587589/tentacle Tentacle] at the ''[[Encyclopædia Britannica]]''
*{{wiktionary-inline}}
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[[Category:Animal anatomy]]
[[Category:Animal morphology]]