Tentacle: Difference between revisions

{{About|tentacles in zoology}}

[[Image:cuttlefish.png|thumb|upright|[[Cuttlefish]] with 2two tentacles and 8eight 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.

=== Molluscs ===

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>

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 et al. (|date=1895). ''|title=The Cambridge Natural History Volume |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. |accessdateaccess-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> It is worth noting however, that whileWhile 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]].

===Cnidarians and ctenophores===

[[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 | accessdateaccess-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]] [[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=httphttps://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>

The word '''tentillum''' (pl.{{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.

{{Commons category-inline|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]]''